fix for #118: replace js/jsx with ts/tsx like tsc

CHANGELOG.md

@@ -2,9 +2,13 @@
 
 ## Unreleased
 
-* Reduce memory usage by 30-40% ([#304](https://github.com/evanw/esbuild/issues/304))
+* Reduce memory usage for large builds by 30-40% ([#304](https://github.com/evanw/esbuild/issues/304))
 
-    This release reduces memory usage. Memory is reduced by ~30% for all builds by avoiding unnecessary per-file symbol maps, and is reduced by an additional ~10% for builds with source maps by preallocating some large arrays relating to source map output.
+    This release reduces memory usage. These specific percentages are likely only accurate for builds with a large number of files. Memory is reduced by ~30% for all builds by avoiding unnecessary per-file symbol maps, and is reduced by an additional ~10% for builds with source maps by preallocating some large arrays relating to source map output.
+
+* Replace `.js` and `.jsx` with `.ts` or `.tsx` when resolving ([#118](https://github.com/evanw/esbuild/issues/118))
+
+    This adds an import path resolution behavior that's specific to the TypeScript compiler where you can use an import path that ends in `.js` or `.jsx` when the correct import path actually ends in `.ts` or `.tsx` instead. See the discussion here for more historical context: https://github.com/microsoft/TypeScript/issues/4595.
 
 ## 0.6.18
 

internal/bundler/bundler_ts_test.go

@@ -759,3 +759,68 @@ func TestTSExportDefaultTypeIssue316(t *testing.T) {
 		},
 	})
 }
+
+func TestTSImplicitExtensions(t *testing.T) {
+	ts_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.ts": `
+				import './pick-js.js'
+				import './pick-ts.js'
+				import './pick-jsx.jsx'
+				import './pick-tsx.jsx'
+				import './order-js.js'
+				import './order-jsx.jsx'
+			`,
+
+			"/pick-js.js": `console.log("correct")`,
+			"/pick-js.ts": `console.log("wrong")`,
+
+			"/pick-ts.jsx": `console.log("wrong")`,
+			"/pick-ts.ts":  `console.log("correct")`,
+
+			"/pick-jsx.jsx": `console.log("correct")`,
+			"/pick-jsx.tsx": `console.log("wrong")`,
+
+			"/pick-tsx.js":  `console.log("wrong")`,
+			"/pick-tsx.tsx": `console.log("correct")`,
+
+			"/order-js.ts":  `console.log("correct")`,
+			"/order-js.tsx": `console.log("wrong")`,
+
+			"/order-jsx.ts":  `console.log("correct")`,
+			"/order-jsx.tsx": `console.log("wrong")`,
+		},
+		entryPaths: []string{"/entry.ts"},
+		options: config.Options{
+			IsBundling:    true,
+			AbsOutputFile: "/out.js",
+		},
+	})
+}
+
+func TestTSImplicitExtensionsMissing(t *testing.T) {
+	ts_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.ts": `
+				import './mjs.mjs'
+				import './cjs.cjs'
+				import './js.js'
+				import './jsx.jsx'
+			`,
+			"/mjs.ts":      ``,
+			"/mjs.tsx":     ``,
+			"/cjs.ts":      ``,
+			"/cjs.tsx":     ``,
+			"/js.js.ts":    ``,
+			"/jsx.jsx.tsx": ``,
+		},
+		entryPaths: []string{"/entry.ts"},
+		options: config.Options{
+			IsBundling:    true,
+			AbsOutputFile: "/out.js",
+		},
+		expectedScanLog: `/entry.ts: error: Could not resolve "./mjs.mjs"
+/entry.ts: error: Could not resolve "./cjs.cjs"
+`,
+	})
+}

internal/bundler/snapshots/snapshots_ts.txt

@@ -167,6 +167,29 @@ class Foo {
 // /a.ts
 console.log(new Foo());
 
+================================================================================
+TestTSImplicitExtensions
+---------- /out.js ----------
+// /pick-js.js
+console.log("correct");
+
+// /pick-ts.ts
+console.log("correct");
+
+// /pick-jsx.jsx
+console.log("correct");
+
+// /pick-tsx.tsx
+console.log("correct");
+
+// /order-js.ts
+console.log("correct");
+
+// /order-jsx.ts
+console.log("correct");
+
+// /entry.ts
+
 ================================================================================
 TestTSImportEmptyNamespace
 ---------- /out.js ----------

internal/resolver/resolver.go

@@ -806,6 +806,32 @@ func (r *resolver) loadAsFile(path string) (string, bool) {
 				return path + ext, true
 			}
 		}
+
+		// TypeScript-specific behavior: if the extension is ".js" or ".jsx", try
+		// replacing it with ".ts" or ".tsx". At the time of writing this specific
+		// behavior comes from the function "loadModuleFromFile()" in the file
+		// "moduleNameResolver.ts" in the TypeScript compiler source code. It
+		// contains this comment:
+		//
+		//   If that didn't work, try stripping a ".js" or ".jsx" extension and
+		//   replacing it with a TypeScript one; e.g. "./foo.js" can be matched
+		//   by "./foo.ts" or "./foo.d.ts"
+		//
+		// We don't care about ".d.ts" files because we can't do anything with
+		// those, so we ignore that part of the behavior.
+		//
+		// See the discussion here for more historical context:
+		// https://github.com/microsoft/TypeScript/issues/4595
+		if strings.HasSuffix(base, ".js") || strings.HasSuffix(base, ".jsx") {
+			lastDot := strings.LastIndexByte(base, '.')
+			// Note that the official compiler code always tries ".ts" before
+			// ".tsx" even if the original extension was ".jsx".
+			for _, ext := range []string{".ts", ".tsx"} {
+				if entries[base[:lastDot]+ext].Kind == fs.FileEntry {
+					return path[:len(path)-(len(base)-lastDot)] + ext, true
+				}
+			}
+		}
 	}
 
 	return "", false