diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index a9577979231..f87f8bea2b7 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -12937,6 +12937,14 @@ namespace ts {
             return (target.flags & TypeFlags.Nullable) !== 0 || isTypeComparableTo(source, target);
         }
 
+        function getBestChoiceType(type1: Type, type2: Type): Type {
+            const firstAssignableToSecond = isTypeAssignableTo(type1, type2);
+            const secondAssignableToFirst = isTypeAssignableTo(type2, type1);
+            return secondAssignableToFirst && !firstAssignableToSecond ? type1 :
+                firstAssignableToSecond && !secondAssignableToFirst ? type2 :
+                getUnionType([type1, type2], /*subtypeReduction*/ true);
+        }
+
         function checkBinaryExpression(node: BinaryExpression, contextualMapper?: TypeMapper) {
             return checkBinaryLikeExpression(node.left, node.operatorToken, node.right, contextualMapper, node);
         }
@@ -13080,7 +13088,7 @@ namespace ts {
                         leftType;
                 case SyntaxKind.BarBarToken:
                     return getTypeFacts(leftType) & TypeFacts.Falsy ?
-                        getUnionType([removeDefinitelyFalsyTypes(leftType), rightType], /*subtypeReduction*/ true) :
+                        getBestChoiceType(removeDefinitelyFalsyTypes(leftType), rightType) :
                         leftType;
                 case SyntaxKind.EqualsToken:
                     checkAssignmentOperator(rightType);
@@ -13207,7 +13215,7 @@ namespace ts {
             checkExpression(node.condition);
             const type1 = checkExpression(node.whenTrue, contextualMapper);
             const type2 = checkExpression(node.whenFalse, contextualMapper);
-            return getUnionType([type1, type2], /*subtypeReduction*/ true);
+            return getBestChoiceType(type1, type2);
         }
 
         function typeContainsLiteralFromEnum(type: Type, enumType: EnumType) {
diff --git a/src/lib/es5.d.ts b/src/lib/es5.d.ts
index 6f017c8a343..496df578c19 100644
--- a/src/lib/es5.d.ts
+++ b/src/lib/es5.d.ts
@@ -1108,6 +1108,11 @@ interface Array<T> {
       * Removes the last element from an array and returns it.
       */
     pop(): T | undefined;
+    /**
+      * Combines two or more arrays.
+      * @param items Additional items to add to the end of array1.
+      */
+    concat(...items: T[][]): T[];
     /**
       * Combines two or more arrays.
       * @param items Additional items to add to the end of array1.
diff --git a/src/services/formatting/formatting.ts b/src/services/formatting/formatting.ts
index 8a27501e684..c17d38421c2 100644
--- a/src/services/formatting/formatting.ts
+++ b/src/services/formatting/formatting.ts
@@ -453,9 +453,9 @@ namespace ts.formatting {
                 case SyntaxKind.MethodDeclaration:
                     if ((<MethodDeclaration>node).asteriskToken) {
                         return SyntaxKind.AsteriskToken;
-                    }
-                    // fall-through
-
+                    }/*
+                    fall-through
+                    */
                 case SyntaxKind.PropertyDeclaration:
                 case SyntaxKind.Parameter:
                     return (<Declaration>node).name.kind;
@@ -732,7 +732,7 @@ namespace ts.formatting {
                         else {
                             // indent token only if end line of previous range does not match start line of the token
                             const prevEndLine = savePreviousRange && sourceFile.getLineAndCharacterOfPosition(savePreviousRange.end).line;
-                            indentToken = lastTriviaWasNewLine &&  tokenStart.line !== prevEndLine;
+                            indentToken = lastTriviaWasNewLine && tokenStart.line !== prevEndLine;
                         }
                     }
                 }
@@ -892,7 +892,7 @@ namespace ts.formatting {
         }
 
         function indentationIsDifferent(indentationString: string, startLinePosition: number): boolean {
-            return indentationString !== sourceFile.text.substr(startLinePosition , indentationString.length);
+            return indentationString !== sourceFile.text.substr(startLinePosition, indentationString.length);
         }
 
         function indentMultilineComment(commentRange: TextRange, indentation: number, firstLineIsIndented: boolean) {
@@ -936,7 +936,7 @@ namespace ts.formatting {
 
             // shift all parts on the delta size
             const delta = indentation - nonWhitespaceColumnInFirstPart.column;
-            for (let i = startIndex, len = parts.length; i < len; i++, startLine++) {
+            for (let i = startIndex, len = parts.length; i < len; i++ , startLine++) {
                 const startLinePos = getStartPositionOfLine(startLine, sourceFile);
                 const nonWhitespaceCharacterAndColumn =
                     i === 0
diff --git a/src/services/formatting/rules.ts b/src/services/formatting/rules.ts
index 1a7f33d3e48..993ea02fb75 100644
--- a/src/services/formatting/rules.ts
+++ b/src/services/formatting/rules.ts
@@ -231,6 +231,13 @@ namespace ts.formatting {
         public NoSpaceBeforeCloseBraceInJsxExpression: Rule;
         public SpaceBeforeCloseBraceInJsxExpression: Rule;
 
+        // JSX opening elements
+        public SpaceBeforeJsxAttribute: Rule;
+        public SpaceBeforeSlashInJsxOpeningElement: Rule;
+        public NoSpaceBeforeGreaterThanTokenInJsxOpeningElement: Rule;
+        public NoSpaceBeforeEqualInJsxAttribute: Rule;
+        public NoSpaceAfterEqualInJsxAttribute: Rule;
+
         constructor() {
             ///
             /// Common Rules
@@ -322,7 +329,7 @@ namespace ts.formatting {
 
             // Add a space between statements. All keywords except (do,else,case) has open/close parens after them.
             // So, we have a rule to add a space for [),Any], [do,Any], [else,Any], and [case,Any]
-            this.SpaceBetweenStatements = new Rule(RuleDescriptor.create4(Shared.TokenRange.FromTokens([SyntaxKind.CloseParenToken, SyntaxKind.DoKeyword, SyntaxKind.ElseKeyword, SyntaxKind.CaseKeyword]), Shared.TokenRange.Any), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext, Rules.isNonJsxElementContext, Rules.IsNotForContext), RuleAction.Space));
+            this.SpaceBetweenStatements = new Rule(RuleDescriptor.create4(Shared.TokenRange.FromTokens([SyntaxKind.CloseParenToken, SyntaxKind.DoKeyword, SyntaxKind.ElseKeyword, SyntaxKind.CaseKeyword]), Shared.TokenRange.Any), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext, Rules.IsNonJsxElementContext, Rules.IsNotForContext), RuleAction.Space));
 
             // This low-pri rule takes care of "try {" and "finally {" in case the rule SpaceBeforeOpenBraceInControl didn't execute on FormatOnEnter.
             this.SpaceAfterTryFinally = new Rule(RuleDescriptor.create2(Shared.TokenRange.FromTokens([SyntaxKind.TryKeyword, SyntaxKind.FinallyKeyword]), SyntaxKind.OpenBraceToken), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext), RuleAction.Space));
@@ -386,6 +393,13 @@ namespace ts.formatting {
             // template string
             this.NoSpaceBetweenTagAndTemplateString = new Rule(RuleDescriptor.create3(SyntaxKind.Identifier, Shared.TokenRange.FromTokens([SyntaxKind.NoSubstitutionTemplateLiteral, SyntaxKind.TemplateHead])), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext), RuleAction.Delete));
 
+            // jsx opening element
+            this.SpaceBeforeJsxAttribute = new Rule(RuleDescriptor.create2(Shared.TokenRange.Any, SyntaxKind.Identifier), RuleOperation.create2(new RuleOperationContext(Rules.IsNextTokenParentJsxAttribute, Rules.IsNonJsxSameLineTokenContext), RuleAction.Space));
+            this.SpaceBeforeSlashInJsxOpeningElement = new Rule(RuleDescriptor.create2(Shared.TokenRange.Any, SyntaxKind.SlashToken), RuleOperation.create2(new RuleOperationContext(Rules.IsJsxSelfClosingElementContext, Rules.IsNonJsxSameLineTokenContext), RuleAction.Space));
+            this.NoSpaceBeforeGreaterThanTokenInJsxOpeningElement = new Rule(RuleDescriptor.create1(SyntaxKind.SlashToken, SyntaxKind.GreaterThanToken), RuleOperation.create2(new RuleOperationContext(Rules.IsJsxSelfClosingElementContext, Rules.IsNonJsxSameLineTokenContext), RuleAction.Delete));
+            this.NoSpaceBeforeEqualInJsxAttribute = new Rule(RuleDescriptor.create2(Shared.TokenRange.Any, SyntaxKind.EqualsToken), RuleOperation.create2(new RuleOperationContext(Rules.IsJsxAttributeContext, Rules.IsNonJsxSameLineTokenContext), RuleAction.Delete));
+            this.NoSpaceAfterEqualInJsxAttribute = new Rule(RuleDescriptor.create3(SyntaxKind.EqualsToken, Shared.TokenRange.Any), RuleOperation.create2(new RuleOperationContext(Rules.IsJsxAttributeContext, Rules.IsNonJsxSameLineTokenContext), RuleAction.Delete));
+
             // These rules are higher in priority than user-configurable rules.
             this.HighPriorityCommonRules = [
                 this.IgnoreBeforeComment, this.IgnoreAfterLineComment,
@@ -413,6 +427,8 @@ namespace ts.formatting {
                 this.SpaceAfterVoidOperator,
                 this.SpaceBetweenAsyncAndOpenParen, this.SpaceBetweenAsyncAndFunctionKeyword,
                 this.NoSpaceBetweenTagAndTemplateString,
+                this.SpaceBeforeJsxAttribute, this.SpaceBeforeSlashInJsxOpeningElement, this.NoSpaceBeforeGreaterThanTokenInJsxOpeningElement,
+                this.NoSpaceBeforeEqualInJsxAttribute, this.NoSpaceAfterEqualInJsxAttribute,
 
                 // TypeScript-specific rules
                 this.NoSpaceAfterConstructor, this.NoSpaceAfterModuleImport,
@@ -450,8 +466,8 @@ namespace ts.formatting {
             ///
 
             // Insert space after comma delimiter
-            this.SpaceAfterComma = new Rule(RuleDescriptor.create3(SyntaxKind.CommaToken, Shared.TokenRange.Any), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext, Rules.isNonJsxElementContext, Rules.IsNextTokenNotCloseBracket), RuleAction.Space));
-            this.NoSpaceAfterComma = new Rule(RuleDescriptor.create3(SyntaxKind.CommaToken, Shared.TokenRange.Any), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext, Rules.isNonJsxElementContext), RuleAction.Delete));
+            this.SpaceAfterComma = new Rule(RuleDescriptor.create3(SyntaxKind.CommaToken, Shared.TokenRange.Any), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext, Rules.IsNonJsxElementContext, Rules.IsNextTokenNotCloseBracket), RuleAction.Space));
+            this.NoSpaceAfterComma = new Rule(RuleDescriptor.create3(SyntaxKind.CommaToken, Shared.TokenRange.Any), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext, Rules.IsNonJsxElementContext), RuleAction.Delete));
 
             // Insert space before and after binary operators
             this.SpaceBeforeBinaryOperator = new Rule(RuleDescriptor.create4(Shared.TokenRange.Any, Shared.TokenRange.BinaryOperators), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext, Rules.IsBinaryOpContext), RuleAction.Space));
@@ -498,10 +514,10 @@ namespace ts.formatting {
             this.SpaceBeforeTemplateMiddleAndTail = new Rule(RuleDescriptor.create4(Shared.TokenRange.Any, Shared.TokenRange.FromTokens([SyntaxKind.TemplateMiddle, SyntaxKind.TemplateTail])), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext), RuleAction.Space));
 
             // No space after { and before } in JSX expression
-            this.NoSpaceAfterOpenBraceInJsxExpression = new Rule(RuleDescriptor.create3(SyntaxKind.OpenBraceToken, Shared.TokenRange.Any), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext, Rules.isJsxExpressionContext), RuleAction.Delete));
-            this.SpaceAfterOpenBraceInJsxExpression = new Rule(RuleDescriptor.create3(SyntaxKind.OpenBraceToken, Shared.TokenRange.Any), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext, Rules.isJsxExpressionContext), RuleAction.Space));
-            this.NoSpaceBeforeCloseBraceInJsxExpression = new Rule(RuleDescriptor.create2(Shared.TokenRange.Any, SyntaxKind.CloseBraceToken), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext, Rules.isJsxExpressionContext), RuleAction.Delete));
-            this.SpaceBeforeCloseBraceInJsxExpression = new Rule(RuleDescriptor.create2(Shared.TokenRange.Any, SyntaxKind.CloseBraceToken), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext, Rules.isJsxExpressionContext), RuleAction.Space));
+            this.NoSpaceAfterOpenBraceInJsxExpression = new Rule(RuleDescriptor.create3(SyntaxKind.OpenBraceToken, Shared.TokenRange.Any), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext, Rules.IsJsxExpressionContext), RuleAction.Delete));
+            this.SpaceAfterOpenBraceInJsxExpression = new Rule(RuleDescriptor.create3(SyntaxKind.OpenBraceToken, Shared.TokenRange.Any), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext, Rules.IsJsxExpressionContext), RuleAction.Space));
+            this.NoSpaceBeforeCloseBraceInJsxExpression = new Rule(RuleDescriptor.create2(Shared.TokenRange.Any, SyntaxKind.CloseBraceToken), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext, Rules.IsJsxExpressionContext), RuleAction.Delete));
+            this.SpaceBeforeCloseBraceInJsxExpression = new Rule(RuleDescriptor.create2(Shared.TokenRange.Any, SyntaxKind.CloseBraceToken), RuleOperation.create2(new RuleOperationContext(Rules.IsNonJsxSameLineTokenContext, Rules.IsJsxExpressionContext), RuleAction.Space));
 
             // Insert space after function keyword for anonymous functions
             this.SpaceAfterAnonymousFunctionKeyword = new Rule(RuleDescriptor.create1(SyntaxKind.FunctionKeyword, SyntaxKind.OpenParenToken), RuleOperation.create2(new RuleOperationContext(Rules.IsFunctionDeclContext), RuleAction.Space));
@@ -741,14 +757,26 @@ namespace ts.formatting {
             return context.TokensAreOnSameLine() && context.contextNode.kind !== SyntaxKind.JsxText;
         }
 
-        static isNonJsxElementContext(context: FormattingContext): boolean {
+        static IsNonJsxElementContext(context: FormattingContext): boolean {
             return context.contextNode.kind !== SyntaxKind.JsxElement;
         }
 
-        static isJsxExpressionContext(context: FormattingContext): boolean {
+        static IsJsxExpressionContext(context: FormattingContext): boolean {
             return context.contextNode.kind === SyntaxKind.JsxExpression;
         }
 
+        static IsNextTokenParentJsxAttribute(context: FormattingContext): boolean {
+            return context.nextTokenParent.kind === SyntaxKind.JsxAttribute;
+        }
+
+        static IsJsxAttributeContext(context: FormattingContext): boolean {
+            return context.contextNode.kind === SyntaxKind.JsxAttribute;
+        }
+
+        static IsJsxSelfClosingElementContext(context: FormattingContext): boolean {
+            return context.contextNode.kind === SyntaxKind.JsxSelfClosingElement;
+        }
+
         static IsNotBeforeBlockInFunctionDeclarationContext(context: FormattingContext): boolean {
             return !Rules.IsFunctionDeclContext(context) && !Rules.IsBeforeBlockContext(context);
         }
diff --git a/src/services/services.ts b/src/services/services.ts
index 7a5110f9913..c09eb21b959 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -3095,14 +3095,16 @@ namespace ts {
 
             const oldSettings = program && program.getCompilerOptions();
             const newSettings = hostCache.compilationSettings();
-            const changesInCompilationSettingsAffectSyntax = oldSettings &&
+            const shouldCreateNewSourceFiles = oldSettings &&
                 (oldSettings.target !== newSettings.target ||
                  oldSettings.module !== newSettings.module ||
                  oldSettings.moduleResolution !== newSettings.moduleResolution ||
                  oldSettings.noResolve !== newSettings.noResolve ||
                  oldSettings.jsx !== newSettings.jsx ||
                  oldSettings.allowJs !== newSettings.allowJs ||
-                 oldSettings.disableSizeLimit !== oldSettings.disableSizeLimit);
+                 oldSettings.disableSizeLimit !== oldSettings.disableSizeLimit ||
+                 oldSettings.baseUrl !== newSettings.baseUrl ||
+                 !mapIsEqualTo(oldSettings.paths, newSettings.paths));
 
             // Now create a new compiler
             const compilerHost: CompilerHost = {
@@ -3154,7 +3156,7 @@ namespace ts {
                 const oldSourceFiles = program.getSourceFiles();
                 const oldSettingsKey = documentRegistry.getKeyForCompilationSettings(oldSettings);
                 for (const oldSourceFile of oldSourceFiles) {
-                    if (!newProgram.getSourceFile(oldSourceFile.fileName) || changesInCompilationSettingsAffectSyntax) {
+                    if (!newProgram.getSourceFile(oldSourceFile.fileName) || shouldCreateNewSourceFiles) {
                         documentRegistry.releaseDocumentWithKey(oldSourceFile.path, oldSettingsKey);
                     }
                 }
@@ -3188,7 +3190,7 @@ namespace ts {
                 // Check if the language version has changed since we last created a program; if they are the same,
                 // it is safe to reuse the sourceFiles; if not, then the shape of the AST can change, and the oldSourceFile
                 // can not be reused. we have to dump all syntax trees and create new ones.
-                if (!changesInCompilationSettingsAffectSyntax) {
+                if (!shouldCreateNewSourceFiles) {
                     // Check if the old program had this file already
                     const oldSourceFile = program && program.getSourceFileByPath(path);
                     if (oldSourceFile) {
diff --git a/tests/baselines/reference/arrayConcat2.symbols b/tests/baselines/reference/arrayConcat2.symbols
index fb84193c113..daedee6e9c8 100644
--- a/tests/baselines/reference/arrayConcat2.symbols
+++ b/tests/baselines/reference/arrayConcat2.symbols
@@ -3,21 +3,21 @@ var a: string[] = [];
 >a : Symbol(a, Decl(arrayConcat2.ts, 0, 3))
 
 a.concat("hello", 'world');
->a.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>a.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 >a : Symbol(a, Decl(arrayConcat2.ts, 0, 3))
->concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 
 a.concat('Hello');
->a.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>a.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 >a : Symbol(a, Decl(arrayConcat2.ts, 0, 3))
->concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 
 var b = new Array<string>();
 >b : Symbol(b, Decl(arrayConcat2.ts, 5, 3))
 >Array : Symbol(Array, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 
 b.concat('hello');
->b.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>b.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 >b : Symbol(b, Decl(arrayConcat2.ts, 5, 3))
->concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 
diff --git a/tests/baselines/reference/arrayConcat2.types b/tests/baselines/reference/arrayConcat2.types
index b7df3749116..27fe754c485 100644
--- a/tests/baselines/reference/arrayConcat2.types
+++ b/tests/baselines/reference/arrayConcat2.types
@@ -5,17 +5,17 @@ var a: string[] = [];
 
 a.concat("hello", 'world');
 >a.concat("hello", 'world') : string[]
->a.concat : (...items: (string | string[])[]) => string[]
+>a.concat : { (...items: string[][]): string[]; (...items: (string | string[])[]): string[]; }
 >a : string[]
->concat : (...items: (string | string[])[]) => string[]
+>concat : { (...items: string[][]): string[]; (...items: (string | string[])[]): string[]; }
 >"hello" : string
 >'world' : string
 
 a.concat('Hello');
 >a.concat('Hello') : string[]
->a.concat : (...items: (string | string[])[]) => string[]
+>a.concat : { (...items: string[][]): string[]; (...items: (string | string[])[]): string[]; }
 >a : string[]
->concat : (...items: (string | string[])[]) => string[]
+>concat : { (...items: string[][]): string[]; (...items: (string | string[])[]): string[]; }
 >'Hello' : string
 
 var b = new Array<string>();
@@ -25,8 +25,8 @@ var b = new Array<string>();
 
 b.concat('hello');
 >b.concat('hello') : string[]
->b.concat : (...items: (string | string[])[]) => string[]
+>b.concat : { (...items: string[][]): string[]; (...items: (string | string[])[]): string[]; }
 >b : string[]
->concat : (...items: (string | string[])[]) => string[]
+>concat : { (...items: string[][]): string[]; (...items: (string | string[])[]): string[]; }
 >'hello' : string
 
diff --git a/tests/baselines/reference/arrayConcatMap.symbols b/tests/baselines/reference/arrayConcatMap.symbols
index bde2686e259..5ef9d811723 100644
--- a/tests/baselines/reference/arrayConcatMap.symbols
+++ b/tests/baselines/reference/arrayConcatMap.symbols
@@ -2,8 +2,8 @@
 var x = [].concat([{ a: 1 }], [{ a: 2 }])
 >x : Symbol(x, Decl(arrayConcatMap.ts, 0, 3))
 >[].concat([{ a: 1 }], [{ a: 2 }])          .map : Symbol(Array.map, Decl(lib.d.ts, --, --))
->[].concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
->concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>[].concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 >a : Symbol(a, Decl(arrayConcatMap.ts, 0, 20))
 >a : Symbol(a, Decl(arrayConcatMap.ts, 0, 32))
 
diff --git a/tests/baselines/reference/arrayConcatMap.types b/tests/baselines/reference/arrayConcatMap.types
index 38e1a1c49c9..647406ef1c3 100644
--- a/tests/baselines/reference/arrayConcatMap.types
+++ b/tests/baselines/reference/arrayConcatMap.types
@@ -4,9 +4,9 @@ var x = [].concat([{ a: 1 }], [{ a: 2 }])
 >[].concat([{ a: 1 }], [{ a: 2 }])          .map(b => b.a) : any[]
 >[].concat([{ a: 1 }], [{ a: 2 }])          .map : <U>(callbackfn: (value: any, index: number, array: any[]) => U, thisArg?: any) => U[]
 >[].concat([{ a: 1 }], [{ a: 2 }]) : any[]
->[].concat : (...items: any[]) => any[]
+>[].concat : { (...items: any[][]): any[]; (...items: any[]): any[]; }
 >[] : undefined[]
->concat : (...items: any[]) => any[]
+>concat : { (...items: any[][]): any[]; (...items: any[]): any[]; }
 >[{ a: 1 }] : { a: number; }[]
 >{ a: 1 } : { a: number; }
 >a : number
diff --git a/tests/baselines/reference/asOpEmitParens.js b/tests/baselines/reference/asOpEmitParens.js
new file mode 100644
index 00000000000..dee8d263eae
--- /dev/null
+++ b/tests/baselines/reference/asOpEmitParens.js
@@ -0,0 +1,19 @@
+//// [asOpEmitParens.ts]
+declare var x;
+// Must emit as (x + 1) * 3
+(x + 1 as number) * 3;
+
+// Should still emit as x.y
+(x as any).y;
+
+// Emit as new (x())
+new (x() as any);
+
+
+//// [asOpEmitParens.js]
+// Must emit as (x + 1) * 3
+(x + 1) * 3;
+// Should still emit as x.y
+x.y;
+// Emit as new (x())
+new (x());
diff --git a/tests/baselines/reference/asOpEmitParens.symbols b/tests/baselines/reference/asOpEmitParens.symbols
new file mode 100644
index 00000000000..210d9f3ea0d
--- /dev/null
+++ b/tests/baselines/reference/asOpEmitParens.symbols
@@ -0,0 +1,16 @@
+=== tests/cases/conformance/expressions/asOperator/asOpEmitParens.ts ===
+declare var x;
+>x : Symbol(x, Decl(asOpEmitParens.ts, 0, 11))
+
+// Must emit as (x + 1) * 3
+(x + 1 as number) * 3;
+>x : Symbol(x, Decl(asOpEmitParens.ts, 0, 11))
+
+// Should still emit as x.y
+(x as any).y;
+>x : Symbol(x, Decl(asOpEmitParens.ts, 0, 11))
+
+// Emit as new (x())
+new (x() as any);
+>x : Symbol(x, Decl(asOpEmitParens.ts, 0, 11))
+
diff --git a/tests/baselines/reference/asOpEmitParens.types b/tests/baselines/reference/asOpEmitParens.types
new file mode 100644
index 00000000000..b87d7f4d91f
--- /dev/null
+++ b/tests/baselines/reference/asOpEmitParens.types
@@ -0,0 +1,30 @@
+=== tests/cases/conformance/expressions/asOperator/asOpEmitParens.ts ===
+declare var x;
+>x : any
+
+// Must emit as (x + 1) * 3
+(x + 1 as number) * 3;
+>(x + 1 as number) * 3 : number
+>(x + 1 as number) : number
+>x + 1 as number : number
+>x + 1 : any
+>x : any
+>1 : number
+>3 : number
+
+// Should still emit as x.y
+(x as any).y;
+>(x as any).y : any
+>(x as any) : any
+>x as any : any
+>x : any
+>y : any
+
+// Emit as new (x())
+new (x() as any);
+>new (x() as any) : any
+>(x() as any) : any
+>x() as any : any
+>x() : any
+>x : any
+
diff --git a/tests/baselines/reference/bestChoiceType.js b/tests/baselines/reference/bestChoiceType.js
new file mode 100644
index 00000000000..0c1bf5df2d4
--- /dev/null
+++ b/tests/baselines/reference/bestChoiceType.js
@@ -0,0 +1,35 @@
+//// [bestChoiceType.ts]
+
+// Repro from #10041
+
+(''.match(/ /) || []).map(s => s.toLowerCase());
+
+// Similar cases
+
+function f1() {
+    let x = ''.match(/ /);
+    let y = x || [];
+    let z = y.map(s => s.toLowerCase());
+}
+
+function f2() {
+    let x = ''.match(/ /);
+    let y = x ? x : [];
+    let z = y.map(s => s.toLowerCase());
+}
+
+
+//// [bestChoiceType.js]
+// Repro from #10041
+(''.match(/ /) || []).map(function (s) { return s.toLowerCase(); });
+// Similar cases
+function f1() {
+    var x = ''.match(/ /);
+    var y = x || [];
+    var z = y.map(function (s) { return s.toLowerCase(); });
+}
+function f2() {
+    var x = ''.match(/ /);
+    var y = x ? x : [];
+    var z = y.map(function (s) { return s.toLowerCase(); });
+}
diff --git a/tests/baselines/reference/bestChoiceType.symbols b/tests/baselines/reference/bestChoiceType.symbols
new file mode 100644
index 00000000000..25f7de2eeda
--- /dev/null
+++ b/tests/baselines/reference/bestChoiceType.symbols
@@ -0,0 +1,63 @@
+=== tests/cases/compiler/bestChoiceType.ts ===
+
+// Repro from #10041
+
+(''.match(/ /) || []).map(s => s.toLowerCase());
+>(''.match(/ /) || []).map : Symbol(Array.map, Decl(lib.d.ts, --, --))
+>''.match : Symbol(String.match, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>match : Symbol(String.match, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>map : Symbol(Array.map, Decl(lib.d.ts, --, --))
+>s : Symbol(s, Decl(bestChoiceType.ts, 3, 26))
+>s.toLowerCase : Symbol(String.toLowerCase, Decl(lib.d.ts, --, --))
+>s : Symbol(s, Decl(bestChoiceType.ts, 3, 26))
+>toLowerCase : Symbol(String.toLowerCase, Decl(lib.d.ts, --, --))
+
+// Similar cases
+
+function f1() {
+>f1 : Symbol(f1, Decl(bestChoiceType.ts, 3, 48))
+
+    let x = ''.match(/ /);
+>x : Symbol(x, Decl(bestChoiceType.ts, 8, 7))
+>''.match : Symbol(String.match, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>match : Symbol(String.match, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+
+    let y = x || [];
+>y : Symbol(y, Decl(bestChoiceType.ts, 9, 7))
+>x : Symbol(x, Decl(bestChoiceType.ts, 8, 7))
+
+    let z = y.map(s => s.toLowerCase());
+>z : Symbol(z, Decl(bestChoiceType.ts, 10, 7))
+>y.map : Symbol(Array.map, Decl(lib.d.ts, --, --))
+>y : Symbol(y, Decl(bestChoiceType.ts, 9, 7))
+>map : Symbol(Array.map, Decl(lib.d.ts, --, --))
+>s : Symbol(s, Decl(bestChoiceType.ts, 10, 18))
+>s.toLowerCase : Symbol(String.toLowerCase, Decl(lib.d.ts, --, --))
+>s : Symbol(s, Decl(bestChoiceType.ts, 10, 18))
+>toLowerCase : Symbol(String.toLowerCase, Decl(lib.d.ts, --, --))
+}
+
+function f2() {
+>f2 : Symbol(f2, Decl(bestChoiceType.ts, 11, 1))
+
+    let x = ''.match(/ /);
+>x : Symbol(x, Decl(bestChoiceType.ts, 14, 7))
+>''.match : Symbol(String.match, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>match : Symbol(String.match, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+
+    let y = x ? x : [];
+>y : Symbol(y, Decl(bestChoiceType.ts, 15, 7))
+>x : Symbol(x, Decl(bestChoiceType.ts, 14, 7))
+>x : Symbol(x, Decl(bestChoiceType.ts, 14, 7))
+
+    let z = y.map(s => s.toLowerCase());
+>z : Symbol(z, Decl(bestChoiceType.ts, 16, 7))
+>y.map : Symbol(Array.map, Decl(lib.d.ts, --, --))
+>y : Symbol(y, Decl(bestChoiceType.ts, 15, 7))
+>map : Symbol(Array.map, Decl(lib.d.ts, --, --))
+>s : Symbol(s, Decl(bestChoiceType.ts, 16, 18))
+>s.toLowerCase : Symbol(String.toLowerCase, Decl(lib.d.ts, --, --))
+>s : Symbol(s, Decl(bestChoiceType.ts, 16, 18))
+>toLowerCase : Symbol(String.toLowerCase, Decl(lib.d.ts, --, --))
+}
+
diff --git a/tests/baselines/reference/bestChoiceType.types b/tests/baselines/reference/bestChoiceType.types
new file mode 100644
index 00000000000..f88cf64e5a2
--- /dev/null
+++ b/tests/baselines/reference/bestChoiceType.types
@@ -0,0 +1,88 @@
+=== tests/cases/compiler/bestChoiceType.ts ===
+
+// Repro from #10041
+
+(''.match(/ /) || []).map(s => s.toLowerCase());
+>(''.match(/ /) || []).map(s => s.toLowerCase()) : string[]
+>(''.match(/ /) || []).map : <U>(callbackfn: (value: string, index: number, array: string[]) => U, thisArg?: any) => U[]
+>(''.match(/ /) || []) : RegExpMatchArray
+>''.match(/ /) || [] : RegExpMatchArray
+>''.match(/ /) : RegExpMatchArray | null
+>''.match : { (regexp: string): RegExpMatchArray | null; (regexp: RegExp): RegExpMatchArray | null; }
+>'' : string
+>match : { (regexp: string): RegExpMatchArray | null; (regexp: RegExp): RegExpMatchArray | null; }
+>/ / : RegExp
+>[] : never[]
+>map : <U>(callbackfn: (value: string, index: number, array: string[]) => U, thisArg?: any) => U[]
+>s => s.toLowerCase() : (s: string) => string
+>s : string
+>s.toLowerCase() : string
+>s.toLowerCase : () => string
+>s : string
+>toLowerCase : () => string
+
+// Similar cases
+
+function f1() {
+>f1 : () => void
+
+    let x = ''.match(/ /);
+>x : RegExpMatchArray | null
+>''.match(/ /) : RegExpMatchArray | null
+>''.match : { (regexp: string): RegExpMatchArray | null; (regexp: RegExp): RegExpMatchArray | null; }
+>'' : string
+>match : { (regexp: string): RegExpMatchArray | null; (regexp: RegExp): RegExpMatchArray | null; }
+>/ / : RegExp
+
+    let y = x || [];
+>y : RegExpMatchArray
+>x || [] : RegExpMatchArray
+>x : RegExpMatchArray | null
+>[] : never[]
+
+    let z = y.map(s => s.toLowerCase());
+>z : string[]
+>y.map(s => s.toLowerCase()) : string[]
+>y.map : <U>(callbackfn: (value: string, index: number, array: string[]) => U, thisArg?: any) => U[]
+>y : RegExpMatchArray
+>map : <U>(callbackfn: (value: string, index: number, array: string[]) => U, thisArg?: any) => U[]
+>s => s.toLowerCase() : (s: string) => string
+>s : string
+>s.toLowerCase() : string
+>s.toLowerCase : () => string
+>s : string
+>toLowerCase : () => string
+}
+
+function f2() {
+>f2 : () => void
+
+    let x = ''.match(/ /);
+>x : RegExpMatchArray | null
+>''.match(/ /) : RegExpMatchArray | null
+>''.match : { (regexp: string): RegExpMatchArray | null; (regexp: RegExp): RegExpMatchArray | null; }
+>'' : string
+>match : { (regexp: string): RegExpMatchArray | null; (regexp: RegExp): RegExpMatchArray | null; }
+>/ / : RegExp
+
+    let y = x ? x : [];
+>y : RegExpMatchArray
+>x ? x : [] : RegExpMatchArray
+>x : RegExpMatchArray | null
+>x : RegExpMatchArray
+>[] : never[]
+
+    let z = y.map(s => s.toLowerCase());
+>z : string[]
+>y.map(s => s.toLowerCase()) : string[]
+>y.map : <U>(callbackfn: (value: string, index: number, array: string[]) => U, thisArg?: any) => U[]
+>y : RegExpMatchArray
+>map : <U>(callbackfn: (value: string, index: number, array: string[]) => U, thisArg?: any) => U[]
+>s => s.toLowerCase() : (s: string) => string
+>s : string
+>s.toLowerCase() : string
+>s.toLowerCase : () => string
+>s : string
+>toLowerCase : () => string
+}
+
diff --git a/tests/baselines/reference/concatError.symbols b/tests/baselines/reference/concatError.symbols
index 23cc55c85be..d4f04531fc7 100644
--- a/tests/baselines/reference/concatError.symbols
+++ b/tests/baselines/reference/concatError.symbols
@@ -14,15 +14,15 @@ var fa: number[];
 
 fa = fa.concat([0]);
 >fa : Symbol(fa, Decl(concatError.ts, 8, 3))
->fa.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>fa.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 >fa : Symbol(fa, Decl(concatError.ts, 8, 3))
->concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 
 fa = fa.concat(0);
 >fa : Symbol(fa, Decl(concatError.ts, 8, 3))
->fa.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>fa.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 >fa : Symbol(fa, Decl(concatError.ts, 8, 3))
->concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 
 
 
diff --git a/tests/baselines/reference/concatError.types b/tests/baselines/reference/concatError.types
index 21a5cc5d089..9624342bd21 100644
--- a/tests/baselines/reference/concatError.types
+++ b/tests/baselines/reference/concatError.types
@@ -16,9 +16,9 @@ fa = fa.concat([0]);
 >fa = fa.concat([0]) : number[]
 >fa : number[]
 >fa.concat([0]) : number[]
->fa.concat : (...items: (number | number[])[]) => number[]
+>fa.concat : { (...items: number[][]): number[]; (...items: (number | number[])[]): number[]; }
 >fa : number[]
->concat : (...items: (number | number[])[]) => number[]
+>concat : { (...items: number[][]): number[]; (...items: (number | number[])[]): number[]; }
 >[0] : number[]
 >0 : number
 
@@ -26,9 +26,9 @@ fa = fa.concat(0);
 >fa = fa.concat(0) : number[]
 >fa : number[]
 >fa.concat(0) : number[]
->fa.concat : (...items: (number | number[])[]) => number[]
+>fa.concat : { (...items: number[][]): number[]; (...items: (number | number[])[]): number[]; }
 >fa : number[]
->concat : (...items: (number | number[])[]) => number[]
+>concat : { (...items: number[][]): number[]; (...items: (number | number[])[]): number[]; }
 >0 : number
 
 
diff --git a/tests/baselines/reference/concatTuples.js b/tests/baselines/reference/concatTuples.js
new file mode 100644
index 00000000000..699c43f210e
--- /dev/null
+++ b/tests/baselines/reference/concatTuples.js
@@ -0,0 +1,8 @@
+//// [concatTuples.ts]
+let ijs: [number, number][] = [[1, 2]];
+ijs = ijs.concat([[3, 4], [5, 6]]);
+
+
+//// [concatTuples.js]
+var ijs = [[1, 2]];
+ijs = ijs.concat([[3, 4], [5, 6]]);
diff --git a/tests/baselines/reference/concatTuples.symbols b/tests/baselines/reference/concatTuples.symbols
new file mode 100644
index 00000000000..a6524f3e1ff
--- /dev/null
+++ b/tests/baselines/reference/concatTuples.symbols
@@ -0,0 +1,10 @@
+=== tests/cases/compiler/concatTuples.ts ===
+let ijs: [number, number][] = [[1, 2]];
+>ijs : Symbol(ijs, Decl(concatTuples.ts, 0, 3))
+
+ijs = ijs.concat([[3, 4], [5, 6]]);
+>ijs : Symbol(ijs, Decl(concatTuples.ts, 0, 3))
+>ijs.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>ijs : Symbol(ijs, Decl(concatTuples.ts, 0, 3))
+>concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+
diff --git a/tests/baselines/reference/concatTuples.types b/tests/baselines/reference/concatTuples.types
new file mode 100644
index 00000000000..3923470b78d
--- /dev/null
+++ b/tests/baselines/reference/concatTuples.types
@@ -0,0 +1,23 @@
+=== tests/cases/compiler/concatTuples.ts ===
+let ijs: [number, number][] = [[1, 2]];
+>ijs : [number, number][]
+>[[1, 2]] : [number, number][]
+>[1, 2] : [number, number]
+>1 : number
+>2 : number
+
+ijs = ijs.concat([[3, 4], [5, 6]]);
+>ijs = ijs.concat([[3, 4], [5, 6]]) : [number, number][]
+>ijs : [number, number][]
+>ijs.concat([[3, 4], [5, 6]]) : [number, number][]
+>ijs.concat : { (...items: [number, number][][]): [number, number][]; (...items: ([number, number] | [number, number][])[]): [number, number][]; }
+>ijs : [number, number][]
+>concat : { (...items: [number, number][][]): [number, number][]; (...items: ([number, number] | [number, number][])[]): [number, number][]; }
+>[[3, 4], [5, 6]] : [number, number][]
+>[3, 4] : [number, number]
+>3 : number
+>4 : number
+>[5, 6] : [number, number]
+>5 : number
+>6 : number
+
diff --git a/tests/baselines/reference/emitSkipsThisWithRestParameter.symbols b/tests/baselines/reference/emitSkipsThisWithRestParameter.symbols
index 4f1e2bc1aec..04a699a322d 100644
--- a/tests/baselines/reference/emitSkipsThisWithRestParameter.symbols
+++ b/tests/baselines/reference/emitSkipsThisWithRestParameter.symbols
@@ -15,9 +15,9 @@ function rebase(fn: (base: any, ...args: any[]) => any): (...args: any[]) => any
 >fn : Symbol(fn, Decl(emitSkipsThisWithRestParameter.ts, 0, 16))
 >apply : Symbol(Function.apply, Decl(lib.d.ts, --, --))
 >this : Symbol(this, Decl(emitSkipsThisWithRestParameter.ts, 1, 20))
->[ this ].concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>[ this ].concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 >this : Symbol(this, Decl(emitSkipsThisWithRestParameter.ts, 1, 20))
->concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 >args : Symbol(args, Decl(emitSkipsThisWithRestParameter.ts, 1, 30))
 
     };
diff --git a/tests/baselines/reference/emitSkipsThisWithRestParameter.types b/tests/baselines/reference/emitSkipsThisWithRestParameter.types
index 97276fa117d..ff6f1e6f73a 100644
--- a/tests/baselines/reference/emitSkipsThisWithRestParameter.types
+++ b/tests/baselines/reference/emitSkipsThisWithRestParameter.types
@@ -18,10 +18,10 @@ function rebase(fn: (base: any, ...args: any[]) => any): (...args: any[]) => any
 >apply : (this: Function, thisArg: any, argArray?: any) => any
 >this : any
 >[ this ].concat(args) : any[]
->[ this ].concat : (...items: any[]) => any[]
+>[ this ].concat : { (...items: any[][]): any[]; (...items: any[]): any[]; }
 >[ this ] : any[]
 >this : any
->concat : (...items: any[]) => any[]
+>concat : { (...items: any[][]): any[]; (...items: any[]): any[]; }
 >args : any[]
 
     };
diff --git a/tests/baselines/reference/iteratorSpreadInArray7.symbols b/tests/baselines/reference/iteratorSpreadInArray7.symbols
index 853e07b908a..57774bcd7ee 100644
--- a/tests/baselines/reference/iteratorSpreadInArray7.symbols
+++ b/tests/baselines/reference/iteratorSpreadInArray7.symbols
@@ -3,9 +3,9 @@ var array: symbol[];
 >array : Symbol(array, Decl(iteratorSpreadInArray7.ts, 0, 3))
 
 array.concat([...new SymbolIterator]);
->array.concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --))
+>array.concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
 >array : Symbol(array, Decl(iteratorSpreadInArray7.ts, 0, 3))
->concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --))
+>concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
 >SymbolIterator : Symbol(SymbolIterator, Decl(iteratorSpreadInArray7.ts, 1, 38))
 
 class SymbolIterator {
diff --git a/tests/baselines/reference/iteratorSpreadInArray7.types b/tests/baselines/reference/iteratorSpreadInArray7.types
index f1dd8ebf855..38549a606ab 100644
--- a/tests/baselines/reference/iteratorSpreadInArray7.types
+++ b/tests/baselines/reference/iteratorSpreadInArray7.types
@@ -4,9 +4,9 @@ var array: symbol[];
 
 array.concat([...new SymbolIterator]);
 >array.concat([...new SymbolIterator]) : symbol[]
->array.concat : (...items: (symbol | symbol[])[]) => symbol[]
+>array.concat : { (...items: symbol[][]): symbol[]; (...items: (symbol | symbol[])[]): symbol[]; }
 >array : symbol[]
->concat : (...items: (symbol | symbol[])[]) => symbol[]
+>concat : { (...items: symbol[][]): symbol[]; (...items: (symbol | symbol[])[]): symbol[]; }
 >[...new SymbolIterator] : symbol[]
 >...new SymbolIterator : symbol
 >new SymbolIterator : SymbolIterator
diff --git a/tests/baselines/reference/nonContextuallyTypedLogicalOr.symbols b/tests/baselines/reference/nonContextuallyTypedLogicalOr.symbols
index 2d921f6631c..43d7539b6b9 100644
--- a/tests/baselines/reference/nonContextuallyTypedLogicalOr.symbols
+++ b/tests/baselines/reference/nonContextuallyTypedLogicalOr.symbols
@@ -28,8 +28,8 @@ var e: Ellement;
 >Ellement : Symbol(Ellement, Decl(nonContextuallyTypedLogicalOr.ts, 3, 1))
 
 (c || e).dummy;
->(c || e).dummy : Symbol(dummy, Decl(nonContextuallyTypedLogicalOr.ts, 0, 22), Decl(nonContextuallyTypedLogicalOr.ts, 5, 20))
+>(c || e).dummy : Symbol(Contextual.dummy, Decl(nonContextuallyTypedLogicalOr.ts, 0, 22))
 >c : Symbol(c, Decl(nonContextuallyTypedLogicalOr.ts, 10, 3))
 >e : Symbol(e, Decl(nonContextuallyTypedLogicalOr.ts, 11, 3))
->dummy : Symbol(dummy, Decl(nonContextuallyTypedLogicalOr.ts, 0, 22), Decl(nonContextuallyTypedLogicalOr.ts, 5, 20))
+>dummy : Symbol(Contextual.dummy, Decl(nonContextuallyTypedLogicalOr.ts, 0, 22))
 
diff --git a/tests/baselines/reference/nonContextuallyTypedLogicalOr.types b/tests/baselines/reference/nonContextuallyTypedLogicalOr.types
index aeb9d1409c6..5061ad1d975 100644
--- a/tests/baselines/reference/nonContextuallyTypedLogicalOr.types
+++ b/tests/baselines/reference/nonContextuallyTypedLogicalOr.types
@@ -29,8 +29,8 @@ var e: Ellement;
 
 (c || e).dummy;
 >(c || e).dummy : any
->(c || e) : Contextual | Ellement
->c || e : Contextual | Ellement
+>(c || e) : Contextual
+>c || e : Contextual
 >c : Contextual
 >e : Ellement
 >dummy : any
diff --git a/tests/baselines/reference/staticAnonymousTypeNotReferencingTypeParameter.symbols b/tests/baselines/reference/staticAnonymousTypeNotReferencingTypeParameter.symbols
index 2596959de9e..f217f42a8d6 100644
--- a/tests/baselines/reference/staticAnonymousTypeNotReferencingTypeParameter.symbols
+++ b/tests/baselines/reference/staticAnonymousTypeNotReferencingTypeParameter.symbols
@@ -300,9 +300,9 @@ class ListWrapper {
 >ListWrapper : Symbol(ListWrapper, Decl(staticAnonymousTypeNotReferencingTypeParameter.ts, 38, 1))
 >a : Symbol(a, Decl(staticAnonymousTypeNotReferencingTypeParameter.ts, 68, 40))
 >b : Symbol(b, Decl(staticAnonymousTypeNotReferencingTypeParameter.ts, 68, 50))
->a.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>a.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 >a : Symbol(a, Decl(staticAnonymousTypeNotReferencingTypeParameter.ts, 68, 40))
->concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 >b : Symbol(b, Decl(staticAnonymousTypeNotReferencingTypeParameter.ts, 68, 50))
 
   static insert<T>(dit: typeof ListWrapper, list: T[], index: number, value: T) { list.splice(index, 0, value); }
diff --git a/tests/baselines/reference/staticAnonymousTypeNotReferencingTypeParameter.types b/tests/baselines/reference/staticAnonymousTypeNotReferencingTypeParameter.types
index e13ac6a64e8..69de032ca2e 100644
--- a/tests/baselines/reference/staticAnonymousTypeNotReferencingTypeParameter.types
+++ b/tests/baselines/reference/staticAnonymousTypeNotReferencingTypeParameter.types
@@ -348,9 +348,9 @@ class ListWrapper {
 >a : any[]
 >b : any[]
 >a.concat(b) : any[]
->a.concat : (...items: any[]) => any[]
+>a.concat : { (...items: any[][]): any[]; (...items: any[]): any[]; }
 >a : any[]
->concat : (...items: any[]) => any[]
+>concat : { (...items: any[][]): any[]; (...items: any[]): any[]; }
 >b : any[]
 
   static insert<T>(dit: typeof ListWrapper, list: T[], index: number, value: T) { list.splice(index, 0, value); }
diff --git a/tests/baselines/reference/subtypingWithObjectMembersOptionality3.types b/tests/baselines/reference/subtypingWithObjectMembersOptionality3.types
index 000d1cdc8ed..6490b0abd9b 100644
--- a/tests/baselines/reference/subtypingWithObjectMembersOptionality3.types
+++ b/tests/baselines/reference/subtypingWithObjectMembersOptionality3.types
@@ -69,8 +69,8 @@ var b: { Foo2: Derived; }
 >Derived : Derived
 
 var r = true ? a : b; // ok
->r : { Foo?: Base; } | { Foo2: Derived; }
->true ? a : b : { Foo?: Base; } | { Foo2: Derived; }
+>r : { Foo?: Base; }
+>true ? a : b : { Foo?: Base; }
 >true : boolean
 >a : { Foo?: Base; }
 >b : { Foo2: Derived; }
diff --git a/tests/baselines/reference/subtypingWithObjectMembersOptionality4.types b/tests/baselines/reference/subtypingWithObjectMembersOptionality4.types
index 2dcda59f46f..ee636be020b 100644
--- a/tests/baselines/reference/subtypingWithObjectMembersOptionality4.types
+++ b/tests/baselines/reference/subtypingWithObjectMembersOptionality4.types
@@ -69,8 +69,8 @@ var b: { Foo2?: Derived; }
 >Derived : Derived
 
 var r = true ? a : b; // ok
->r : { Foo: Base; } | { Foo2?: Derived; }
->true ? a : b : { Foo: Base; } | { Foo2?: Derived; }
+>r : { Foo2?: Derived; }
+>true ? a : b : { Foo2?: Derived; }
 >true : boolean
 >a : { Foo: Base; }
 >b : { Foo2?: Derived; }
diff --git a/tests/baselines/reference/umdGlobalMerge.errors.txt b/tests/baselines/reference/umdGlobalMerge.errors.txt
deleted file mode 100644
index eb4a116ef09..00000000000
--- a/tests/baselines/reference/umdGlobalMerge.errors.txt
+++ /dev/null
@@ -1,20 +0,0 @@
-tests/cases/compiler/b.d.ts(2,20): error TS2305: Module '"tests/cases/compiler/a".ns' has no exported member 'IFoo'.
-
-
-==== tests/cases/compiler/a.d.ts (0 errors) ====
-    export = ns;
-    
-    export as namespace ns;
-    
-    declare namespace ns {
-      export var x: number;
-      export interface IFoo { }
-    }
-    
-==== tests/cases/compiler/b.d.ts (1 errors) ====
-    declare namespace ns.something {
-      export var p: ns.IFoo;
-                       ~~~~
-!!! error TS2305: Module '"tests/cases/compiler/a".ns' has no exported member 'IFoo'.
-    }
-    
\ No newline at end of file
diff --git a/tests/baselines/reference/underscoreTest1.symbols b/tests/baselines/reference/underscoreTest1.symbols
index 3506f23510e..89815bd2371 100644
--- a/tests/baselines/reference/underscoreTest1.symbols
+++ b/tests/baselines/reference/underscoreTest1.symbols
@@ -71,9 +71,9 @@ var flat = _.reduceRight(list, (a, b) => a.concat(b), []);
 >list : Symbol(list, Decl(underscoreTest1_underscoreTests.ts, 13, 3))
 >a : Symbol(a, Decl(underscoreTest1_underscoreTests.ts, 14, 32))
 >b : Symbol(b, Decl(underscoreTest1_underscoreTests.ts, 14, 34))
->a.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>a.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 >a : Symbol(a, Decl(underscoreTest1_underscoreTests.ts, 14, 32))
->concat : Symbol(Array.concat, Decl(lib.d.ts, --, --))
+>concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
 >b : Symbol(b, Decl(underscoreTest1_underscoreTests.ts, 14, 34))
 
 var even = _.find([1, 2, 3, 4, 5, 6], (num) => num % 2 == 0);
diff --git a/tests/baselines/reference/underscoreTest1.types b/tests/baselines/reference/underscoreTest1.types
index a1fd2888bf3..5950e50efa1 100644
--- a/tests/baselines/reference/underscoreTest1.types
+++ b/tests/baselines/reference/underscoreTest1.types
@@ -124,9 +124,9 @@ var flat = _.reduceRight(list, (a, b) => a.concat(b), []);
 >a : number[]
 >b : number[]
 >a.concat(b) : number[]
->a.concat : (...items: (number | number[])[]) => number[]
+>a.concat : { (...items: number[][]): number[]; (...items: (number | number[])[]): number[]; }
 >a : number[]
->concat : (...items: (number | number[])[]) => number[]
+>concat : { (...items: number[][]): number[]; (...items: (number | number[])[]): number[]; }
 >b : number[]
 >[] : undefined[]
 
diff --git a/tests/cases/compiler/bestChoiceType.ts b/tests/cases/compiler/bestChoiceType.ts
new file mode 100644
index 00000000000..3f8ce4bc868
--- /dev/null
+++ b/tests/cases/compiler/bestChoiceType.ts
@@ -0,0 +1,19 @@
+// @strictNullChecks: true
+
+// Repro from #10041
+
+(''.match(/ /) || []).map(s => s.toLowerCase());
+
+// Similar cases
+
+function f1() {
+    let x = ''.match(/ /);
+    let y = x || [];
+    let z = y.map(s => s.toLowerCase());
+}
+
+function f2() {
+    let x = ''.match(/ /);
+    let y = x ? x : [];
+    let z = y.map(s => s.toLowerCase());
+}
diff --git a/tests/cases/compiler/concatTuples.ts b/tests/cases/compiler/concatTuples.ts
new file mode 100644
index 00000000000..9a62f22bb63
--- /dev/null
+++ b/tests/cases/compiler/concatTuples.ts
@@ -0,0 +1,2 @@
+let ijs: [number, number][] = [[1, 2]];
+ijs = ijs.concat([[3, 4], [5, 6]]);
diff --git a/tests/cases/compiler/umdGlobalMerge.ts b/tests/cases/compiler/umdGlobalMerge.ts
deleted file mode 100644
index 1f42e2fda71..00000000000
--- a/tests/cases/compiler/umdGlobalMerge.ts
+++ /dev/null
@@ -1,14 +0,0 @@
-// @filename: a.d.ts
-export = ns;
-
-export as namespace ns;
-
-declare namespace ns {
-  export var x: number;
-  export interface IFoo { }
-}
-
-// @filename: b.d.ts
-declare namespace ns.something {
-  export var p: ns.IFoo;
-}
diff --git a/tests/cases/conformance/expressions/asOperator/asOpEmitParens.ts b/tests/cases/conformance/expressions/asOperator/asOpEmitParens.ts
new file mode 100644
index 00000000000..7a97a74168a
--- /dev/null
+++ b/tests/cases/conformance/expressions/asOperator/asOpEmitParens.ts
@@ -0,0 +1,9 @@
+declare var x;
+// Must emit as (x + 1) * 3
+(x + 1 as number) * 3;
+
+// Should still emit as x.y
+(x as any).y;
+
+// Emit as new (x())
+new (x() as any);
diff --git a/tests/cases/fourslash/formattingJsxElements.ts b/tests/cases/fourslash/formattingJsxElements.ts
index e07149960db..2b3b396ed4c 100644
--- a/tests/cases/fourslash/formattingJsxElements.ts
+++ b/tests/cases/fourslash/formattingJsxElements.ts
@@ -70,7 +70,7 @@
 ////<div>,   {integer}</div>;/*commaInJsxElement2*/
 ////<span>)</span>;/*closingParenInJsxElement*/
 ////<span>)   </span>;/*closingParenInJsxElement2*/
-////<Router routes={                3    } />;/*jsxExpressionSpaces*/
+////<Router        routes      =        { 3 }   /      >;/*jsxExpressionSpaces*/
 ////<Router routes={                (3)    } />;/*jsxExpressionSpaces2*/
 
 format.document();
@@ -85,7 +85,7 @@ goTo.marker("indent1");
 verify.indentationIs(12);
 
 goTo.marker("1");
-verify.currentLineContentIs('            class1= {');
+verify.currentLineContentIs('            class1={');
 goTo.marker("2");
 verify.currentLineContentIs('            }>');
 
@@ -95,7 +95,7 @@ goTo.marker("indent2");
 verify.indentationIs(12);
 
 goTo.marker("3");
-verify.currentLineContentIs('            class2= {');
+verify.currentLineContentIs('            class2={');
 goTo.marker("4");
 verify.currentLineContentIs('            }>');
 
@@ -105,9 +105,9 @@ goTo.marker("indent3");
 verify.indentationIs(12);
 
 goTo.marker("5");
-verify.currentLineContentIs('            class3= {');
+verify.currentLineContentIs('            class3={');
 goTo.marker("6");
-verify.currentLineContentIs('            }/>');
+verify.currentLineContentIs('            } />');
 
 
 goTo.marker("attrAutoformat");