Implement microsoft#35656

Author: Roy Tinker

src/compiler/commandLineParser.ts

@@ -273,18 +273,7 @@ namespace ts {
         {
             name: "target",
             shortName: "t",
-            type: createMapFromTemplate({
-                es3: ScriptTarget.ES3,
-                es5: ScriptTarget.ES5,
-                es6: ScriptTarget.ES2015,
-                es2015: ScriptTarget.ES2015,
-                es2016: ScriptTarget.ES2016,
-                es2017: ScriptTarget.ES2017,
-                es2018: ScriptTarget.ES2018,
-                es2019: ScriptTarget.ES2019,
-                es2020: ScriptTarget.ES2020,
-                esnext: ScriptTarget.ESNext,
-            }),
+            type: ScriptTargetMap,
             affectsSourceFile: true,
             affectsModuleResolution: true,
             affectsEmit: true,

src/compiler/parser.ts

@@ -8186,6 +8186,19 @@ namespace ts {
                     });
                     break;
                 }
+                case "compilerOptions": {
+                    forEach(toArray(entryOrList), entry => {
+                        // _last_ compilerOptions target value in a file is the "winner"
+                        const targetKey = (entry as PragmaPseudoMap["compilerOptions"]).arguments.target;
+                        if (ScriptTargetMap.has(targetKey)) {
+                            context.languageVersion = ScriptTargetMap.get(targetKey) as ScriptTarget;
+                        }
+                        else {
+                            Debug.fail(`Unrecognized compilerOptions target in XML pragma: ${targetKey}`);
+                        }
+                    });
+                    break;
+                }
                 case "jsx": return; // Accessed directly
                 default: Debug.fail("Unhandled pragma kind"); // Can this be made into an assertNever in the future?
             }

src/compiler/types.ts

@@ -5163,6 +5163,20 @@ namespace ts {
         Latest = ESNext,
     }
 
+    export const ScriptTargetMap = createMapFromTemplate({
+        es3: ScriptTarget.ES3,
+        es5: ScriptTarget.ES5,
+        es6: ScriptTarget.ES2015,
+        es2015: ScriptTarget.ES2015,
+        es2016: ScriptTarget.ES2016,
+        es2017: ScriptTarget.ES2017,
+        es2018: ScriptTarget.ES2018,
+        es2019: ScriptTarget.ES2019,
+        es2020: ScriptTarget.ES2020,
+        esnext: ScriptTarget.ESNext,
+    });
+    Object.freeze(ScriptTargetMap);
+
     export const enum LanguageVariant {
         Standard,
         JSX
@@ -6454,6 +6468,10 @@ namespace ts {
             args: [{ name: "name" }],
             kind: PragmaKindFlags.TripleSlashXML
         },
+        "compilerOptions": {
+            args: [{ name: "target" }],
+            kind: PragmaKindFlags.TripleSlashXML
+        },
         "ts-check": {
             kind: PragmaKindFlags.SingleLine
         },