From d0f8be535e32f7225639949ba211f3dbd1c2ab09 Mon Sep 17 00:00:00 2001
From: Nathan Shively-Sanders <nathansa@microsoft.com>
Date: Mon, 12 Sep 2016 14:11:47 -0700
Subject: [PATCH] Enum assignability:loosen numbers+tighten computed

1. All numbers and numeric literals are assignable to all enums and enum
literals.
2. Computed enums are no longer assignable to anything except
themselves, even if they would otherwise be "semi-structurally"
compatible.
---
 src/compiler/checker.ts | 25 +++++++------------------
 1 file changed, 7 insertions(+), 18 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index dc634d25734..28accd8452a 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -6200,9 +6200,10 @@ namespace ts {
             if (enumRelation[id] !== undefined) {
                 return enumRelation[id];
             }
-            if (source.symbol.name !== target.symbol.name || !(source.symbol.flags & SymbolFlags.RegularEnum) || !(target.symbol.flags & SymbolFlags.RegularEnum)) {
-                enumRelation[id] = false;
-                return false;
+            if (source.symbol.name !== target.symbol.name ||
+                !(source.symbol.flags & SymbolFlags.RegularEnum) || !(target.symbol.flags & SymbolFlags.RegularEnum) ||
+                !(source.flags & TypeFlags.Union) || !(target.flags & TypeFlags.Union)) {
+                return (enumRelation[id] = false);
             }
             const targetEnumType = getTypeOfSymbol(target.symbol);
             for (const property of getPropertiesOfType(getTypeOfSymbol(source.symbol))) {
@@ -6213,13 +6214,11 @@ namespace ts {
                             errorReporter(Diagnostics.Property_0_is_missing_in_type_1, property.name,
                                 typeToString(target, /*enclosingDeclaration*/ undefined, TypeFormatFlags.UseFullyQualifiedType));
                         }
-                        enumRelation[id] = false;
-                        return false;
+                        return (enumRelation[id] = false);
                     }
                 }
             }
-            enumRelation[id] = true;
-            return true;
+            return (enumRelation[id] = true);
         }
 
         function isSimpleTypeRelatedTo(source: Type, target: Type, relation: Map<RelationComparisonResult>, errorReporter?: ErrorReporter) {
@@ -6234,9 +6233,7 @@ namespace ts {
             if (source.flags & TypeFlags.Null && (!strictNullChecks || target.flags & TypeFlags.Null)) return true;
             if (relation === assignableRelation || relation === comparableRelation) {
                 if (source.flags & TypeFlags.Any) return true;
-                if (source.flags & TypeFlags.Number && target.flags & TypeFlags.EnumLike) return true;
-                if (source.flags & TypeFlags.NumberLiteral && target.flags & TypeFlags.Enum) return true;
-                if (source.flags & TypeFlags.NumberLiteral && target.flags & TypeFlags.EnumLiteral && (<LiteralType>source).text === (<LiteralType>target).text) return true;
+                if ((source.flags & TypeFlags.Number | source.flags & TypeFlags.NumberLiteral) && target.flags & TypeFlags.EnumLike) return true;
                 if (source.flags & TypeFlags.EnumLiteral &&
                     target.flags & TypeFlags.EnumLiteral &&
                     (<LiteralType>source).text === (<LiteralType>target).text &&
@@ -6423,14 +6420,6 @@ namespace ts {
                         if (result = typeRelatedToSomeType(source, <UnionType>target, reportErrors && !(source.flags & TypeFlags.Primitive) && !(target.flags & TypeFlags.Primitive))) {
                             return result;
                         }
-                        if (source.flags & TypeFlags.Enum) {
-                            // 1. look through the target union for a literal whose base type is related to the source
-                            const lit = find((<UnionType>target).types, t => t.flags & TypeFlags.EnumLiteral && isEnumTypeRelatedTo(<EnumType>source, (<EnumLiteralType>t).baseType));
-                            // 2. if found, the base type is only assignable to source if all its literals are in the target union.
-                            if (lit && (result = isRelatedTo((lit as EnumLiteralType).baseType, target, /*reportErrors*/ false))) {
-                                return result;
-                            }
-                        }
                     }
                 }