Merge pull request #15791 from Microsoft/fix13935

Adds CommaList to avoid large deeply nested comma expressions

src/compiler/core.ts

@@ -490,6 +490,35 @@ namespace ts {
         return result;
     }
 
+    /**
+     * Maps an array. If the mapped value is an array, it is spread into the result.
+     * Avoids allocation if all elements map to themselves.
+     *
+     * @param array The array to map.
+     * @param mapfn The callback used to map the result into one or more values.
+     */
+    export function sameFlatMap<T>(array: T[], mapfn: (x: T, i: number) => T | T[]): T[] {
+        let result: T[];
+        if (array) {
+            for (let i = 0; i < array.length; i++) {
+                const item = array[i];
+                const mapped = mapfn(item, i);
+                if (result || item !== mapped || isArray(mapped)) {
+                    if (!result) {
+                        result = array.slice(0, i);
+                    }
+                    if (isArray(mapped)) {
+                        addRange(result, mapped);
+                    }
+                    else {
+                        result.push(mapped);
+                    }
+                }
+            }
+        }
+        return result || array;
+    }
+
     /**
      * Computes the first matching span of elements and returns a tuple of the first span
      * and the remaining elements.

src/compiler/emitter.ts

@@ -733,6 +733,9 @@ namespace ts {
                 // Transformation nodes
                 case SyntaxKind.PartiallyEmittedExpression:
                     return emitPartiallyEmittedExpression(<PartiallyEmittedExpression>node);
+
+                case SyntaxKind.CommaListExpression:
+                    return emitCommaList(<CommaListExpression>node);
             }
         }
 
@@ -2101,6 +2104,10 @@ namespace ts {
             emitExpression(node.expression);
         }
 
+        function emitCommaList(node: CommaListExpression) {
+            emitExpressionList(node, node.elements, ListFormat.CommaListElements);
+        }
+
         /**
          * Emits any prologue directives at the start of a Statement list, returning the
          * number of prologue directives written to the output.
@@ -2951,6 +2958,7 @@ namespace ts {
         ArrayBindingPatternElements = SingleLine | AllowTrailingComma | CommaDelimited | SpaceBetweenSiblings,
         ObjectLiteralExpressionProperties = PreserveLines | CommaDelimited | SpaceBetweenSiblings | SpaceBetweenBraces | Indented | Braces,
         ArrayLiteralExpressionElements = PreserveLines | CommaDelimited | SpaceBetweenSiblings | AllowTrailingComma | Indented | SquareBrackets,
+        CommaListElements = CommaDelimited | SpaceBetweenSiblings | SingleLine,
         CallExpressionArguments = CommaDelimited | SpaceBetweenSiblings | SingleLine | Parenthesis,
         NewExpressionArguments = CommaDelimited | SpaceBetweenSiblings | SingleLine | Parenthesis | OptionalIfUndefined,
         TemplateExpressionSpans = SingleLine | NoInterveningComments,

src/compiler/factory.ts

@@ -2077,6 +2077,30 @@ namespace ts {
         return node;
     }
 
+    function flattenCommaElements(node: Expression): Expression | Expression[] {
+        if (nodeIsSynthesized(node) && !isParseTreeNode(node) && !node.original && !node.emitNode && !node.id) {
+            if (node.kind === SyntaxKind.CommaListExpression) {
+                return (<CommaListExpression>node).elements;
+            }
+            if (isBinaryExpression(node) && node.operatorToken.kind === SyntaxKind.CommaToken) {
+                return [node.left, node.right];
+            }
+        }
+        return node;
+    }
+
+    export function createCommaList(elements: Expression[]) {
+        const node = <CommaListExpression>createSynthesizedNode(SyntaxKind.CommaListExpression);
+        node.elements = createNodeArray(sameFlatMap(elements, flattenCommaElements));
+        return node;
+    }
+
+    export function updateCommaList(node: CommaListExpression, elements: Expression[]) {
+        return node.elements !== elements
+            ? updateNode(createCommaList(elements), node)
+            : node;
+    }
+
     export function createBundle(sourceFiles: SourceFile[]) {
         const node = <Bundle>createNode(SyntaxKind.Bundle);
         node.sourceFiles = sourceFiles;
@@ -2865,7 +2889,11 @@ namespace ts {
     }
 
     export function inlineExpressions(expressions: Expression[]) {
-        return reduceLeft(expressions, createComma);
+        // Avoid deeply nested comma expressions as traversing them during emit can result in "Maximum call
+        // stack size exceeded" errors.
+        return expressions.length > 10
+            ? createCommaList(expressions)
+            : reduceLeft(expressions, createComma);
     }
 
     export function createExpressionFromEntityName(node: EntityName | Expression): Expression {

src/compiler/parser.ts

@@ -362,6 +362,8 @@ namespace ts {
                 return visitNode(cbNode, (<ExternalModuleReference>node).expression);
             case SyntaxKind.MissingDeclaration:
                 return visitNodes(cbNodes, node.decorators);
+            case SyntaxKind.CommaListExpression:
+                return visitNodes(cbNodes, (<CommaListExpression>node).elements);
 
             case SyntaxKind.JsxElement:
                 return visitNode(cbNode, (<JsxElement>node).openingElement) ||

src/compiler/types.ts

@@ -389,6 +389,7 @@ namespace ts {
         // Transformation nodes
         NotEmittedStatement,
         PartiallyEmittedExpression,
+        CommaListExpression,
         MergeDeclarationMarker,
         EndOfDeclarationMarker,
 
@@ -1603,6 +1604,14 @@ namespace ts {
         kind: SyntaxKind.EndOfDeclarationMarker;
     }
 
+    /**
+     * A list of comma-seperated expressions. This node is only created by transformations.
+     */
+    export interface CommaListExpression extends Expression {
+        kind: SyntaxKind.CommaListExpression;
+        elements: NodeArray<Expression>;
+    }
+
     /**
      * Marks the beginning of a merged transformed declaration.
      */

src/compiler/utilities.ts

@@ -2327,6 +2327,9 @@ namespace ts {
             case SyntaxKind.SpreadElement:
                 return 1;
 
+            case SyntaxKind.CommaListExpression:
+                return 0;
+
             default:
                 return -1;
         }
@@ -3915,6 +3918,7 @@ namespace ts {
             || kind === SyntaxKind.SpreadElement
             || kind === SyntaxKind.AsExpression
             || kind === SyntaxKind.OmittedExpression
+            || kind === SyntaxKind.CommaListExpression
             || isUnaryExpressionKind(kind);
     }
 

src/compiler/visitor.ts

@@ -876,6 +876,10 @@ namespace ts {
                 return updatePartiallyEmittedExpression(<PartiallyEmittedExpression>node,
                     visitNode((<PartiallyEmittedExpression>node).expression, visitor, isExpression));
 
+            case SyntaxKind.CommaListExpression:
+                return updateCommaList(<CommaListExpression>node,
+                    nodesVisitor((<CommaListExpression>node).elements, visitor, isExpression));
+
             default:
                 // No need to visit nodes with no children.
                 return node;
@@ -1389,6 +1393,10 @@ namespace ts {
                 result = reduceNode((<PartiallyEmittedExpression>node).expression, cbNode, result);
                 break;
 
+            case SyntaxKind.CommaListExpression:
+                result = reduceNodes((<CommaListExpression>node).elements, cbNodes, result);
+                break;
+
             default:
                 break;
         }