Fix emitted file extension for JavaScript files with JSX.Preserve

(cherry picked from commit af0a0eedd8)

src/compiler/utilities.ts

@@ -2040,8 +2040,22 @@ namespace ts {
         }
 
         function onSingleFileEmit(host: EmitHost, sourceFile: SourceFile) {
-            const jsFilePath = getOwnEmitOutputFilePath(sourceFile, host,
-                sourceFile.languageVariant === LanguageVariant.JSX && options.jsx === JsxEmit.Preserve ? ".jsx" : ".js");
+            // JavaScript files are always LanguageVariant.JSX, as JSX syntax is allowed in .js files also.
+            // So for JavaScript files, '.jsx' is only emitted if the input was '.jsx', and JsxEmit.Preserve.
+            // For TypeScript, the only time to emit with a '.jsx' extension, is on JSX input, and JsxEmit.Preserve
+            let extension = ".js";
+            if (options.jsx === JsxEmit.Preserve) {
+                if (isSourceFileJavaScript(sourceFile)) {
+                    if (fileExtensionIs(sourceFile.fileName, ".jsx")) {
+                        extension = ".jsx";
+                    }
+                }
+                else if (sourceFile.languageVariant === LanguageVariant.JSX) {
+                    // TypeScript source file preserving JSX syntax
+                    extension = ".jsx";
+                }
+            }
+            const jsFilePath = getOwnEmitOutputFilePath(sourceFile, host, extension);
             const emitFileNames: EmitFileNames = {
                 jsFilePath,
                 sourceMapFilePath: getSourceMapFilePath(jsFilePath, options),

tests/baselines/reference/jsxPreserveWithJsInput.js

@@ -0,0 +1,29 @@
+//// [tests/cases/compiler/jsxPreserveWithJsInput.ts] ////
+
+//// [a.js]
+
+var elemA = 42;
+
+//// [b.jsx]
+var elemB = <b>{"test"}</b>;
+
+//// [c.js]
+var elemC = <c>{42}</c>;
+
+//// [d.ts]
+var elemD = 42;
+
+//// [e.tsx]
+var elemE = <e>{true}</e>;
+
+
+//// [a.js]
+var elemA = 42;
+//// [b.jsx]
+var elemB = <b>{"test"}</b>;
+//// [c.js]
+var elemC = <c>{42}</c>;
+//// [d.js]
+var elemD = 42;
+//// [e.jsx]
+var elemE = <e>{true}</e>;

tests/baselines/reference/jsxPreserveWithJsInput.symbols

@@ -0,0 +1,27 @@
+=== tests/cases/compiler/a.js ===
+
+var elemA = 42;
+>elemA : Symbol(elemA, Decl(a.js, 1, 3))
+
+=== tests/cases/compiler/b.jsx ===
+var elemB = <b>{"test"}</b>;
+>elemB : Symbol(elemB, Decl(b.jsx, 0, 3))
+>b : Symbol(unknown)
+>b : Symbol(unknown)
+
+=== tests/cases/compiler/c.js ===
+var elemC = <c>{42}</c>;
+>elemC : Symbol(elemC, Decl(c.js, 0, 3))
+>c : Symbol(unknown)
+>c : Symbol(unknown)
+
+=== tests/cases/compiler/d.ts ===
+var elemD = 42;
+>elemD : Symbol(elemD, Decl(d.ts, 0, 3))
+
+=== tests/cases/compiler/e.tsx ===
+var elemE = <e>{true}</e>;
+>elemE : Symbol(elemE, Decl(e.tsx, 0, 3))
+>e : Symbol(unknown)
+>e : Symbol(unknown)
+

tests/baselines/reference/jsxPreserveWithJsInput.types

@@ -0,0 +1,35 @@
+=== tests/cases/compiler/a.js ===
+
+var elemA = 42;
+>elemA : number
+>42 : number
+
+=== tests/cases/compiler/b.jsx ===
+var elemB = <b>{"test"}</b>;
+>elemB : any
+><b>{"test"}</b> : any
+>b : any
+>"test" : string
+>b : any
+
+=== tests/cases/compiler/c.js ===
+var elemC = <c>{42}</c>;
+>elemC : any
+><c>{42}</c> : any
+>c : any
+>42 : number
+>c : any
+
+=== tests/cases/compiler/d.ts ===
+var elemD = 42;
+>elemD : number
+>42 : number
+
+=== tests/cases/compiler/e.tsx ===
+var elemE = <e>{true}</e>;
+>elemE : any
+><e>{true}</e> : any
+>e : any
+>true : boolean
+>e : any
+

tests/cases/compiler/jsxPreserveWithJsInput.ts

@@ -0,0 +1,18 @@
+// @outdir: out
+// @jsx: preserve
+// @allowjs: true
+
+// @filename: a.js
+var elemA = 42;
+
+// @filename: b.jsx
+var elemB = <b>{"test"}</b>;
+
+// @filename: c.js
+var elemC = <c>{42}</c>;
+
+// @filename: d.ts
+var elemD = 42;
+
+// @filename: e.tsx
+var elemE = <e>{true}</e>;