fix #560: avoid a warning for "require.main"

CHANGELOG.md

@@ -6,6 +6,10 @@
 
     The return value of the `build` API has some optional fields that are undefined unless certain arguments are present. That meant you had to use the `!` null assertion operator to avoid a type error if you have the TypeScript `strictNullChecks` setting enabled in your project. This release adds additional type information so that if the relevant arguments are present, the TypeScript compiler can tell that these optional fields on the return value will never be undefined. This change was contributed by [@lukeed](https://github.com/lukeed).
 
+* Omit a warning about `require.main` when targeting CommonJS ([#560](https://github.com/evanw/esbuild/issues/560))
+
+    A common pattern in code that's intended to be run in node is to check if `require.main === module`. That will be true if the current file is being run from the command line but false if the current file is being run because some other code called `require()` on it. Previously esbuild generated a warning about an unexpected use of `require`. Now this warning is no longer generated for `require.main` when the output format is `cjs`.
+
 ## 0.8.15
 
 * Allow `paths` without `baseUrl` in `tsconfig.json`

internal/bundler/bundler_default_test.go

@@ -3683,3 +3683,41 @@ func TestConstWithLetNoMangle(t *testing.T) {
 		},
 	})
 }
+
+func TestRequireMainCommonJS(t *testing.T) {
+	default_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.js": `
+				console.log('is main:', require.main === module)
+				console.log(require('./is-main'))
+			`,
+			"/is-main.js": `
+				module.exports = require.main === module
+			`,
+		},
+		entryPaths: []string{"/entry.js"},
+		options: config.Options{
+			Mode:          config.ModeBundle,
+			AbsOutputFile: "/out.js",
+			OutputFormat:  config.FormatCommonJS,
+		},
+	})
+}
+
+func TestRequireMainIIFE(t *testing.T) {
+	default_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.js": `
+				console.log('is main:', require.main === module)
+			`,
+		},
+		entryPaths: []string{"/entry.js"},
+		options: config.Options{
+			Mode:          config.ModeBundle,
+			AbsOutputFile: "/out.js",
+			OutputFormat:  config.FormatIIFE,
+		},
+		expectedScanLog: `/entry.js: warning: Indirect calls to "require" will not be bundled (surround with a try/catch to silence this warning)
+`,
+	})
+}

internal/bundler/snapshots/snapshots_default.txt

@@ -1818,6 +1818,29 @@ var require_test = __commonJS((exports, module) => {
 // /entry.js
 console.log(require_test());
 
+================================================================================
+TestRequireMainCommonJS
+---------- /out.js ----------
+// /is-main.js
+var require_is_main = __commonJS((exports2, module2) => {
+  module2.exports = require.main === module2;
+});
+
+// /entry.js
+console.log("is main:", require.main === module);
+console.log(require_is_main());
+
+================================================================================
+TestRequireMainIIFE
+---------- /out.js ----------
+(() => {
+  // /entry.js
+  var require_entry = __commonJS((exports, module) => {
+    console.log("is main:", require.main === module);
+  });
+  require_entry();
+})();
+
 ================================================================================
 TestRequireParentDirCommonJS
 ---------- /out.js ----------

internal/js_parser/js_parser.go

@@ -195,6 +195,11 @@ type parser struct {
 	typeofRequireEqualsFn       js_ast.E
 	typeofRequireEqualsFnTarget js_ast.E
 
+	// This helps recognize the "require.main" pattern. If this pattern is
+	// present and the output format is CommonJS, we avoid generating a warning
+	// about an unbundled use of "require".
+	cjsDotMainTarget js_ast.E
+
 	// This helps recognize calls to "require.resolve()" which may become
 	// ERequireResolve expressions.
 	resolveCallTarget js_ast.E
@@ -9255,6 +9260,11 @@ func (p *parser) visitExprInOut(expr js_ast.Expr, in exprIn) (js_ast.Expr, exprO
 			}
 		}
 
+		// Pattern-match "require.main" from node
+		if p.options.outputFormat == config.FormatCommonJS && e.Name == "main" {
+			p.cjsDotMainTarget = e.Target.Data
+		}
+
 		isCallTarget := e == p.callTarget
 		target, out := p.visitExprInOut(e.Target, exprIn{
 			hasChainParent: e.OptionalChain == js_ast.OptionalChainContinue,
@@ -9883,7 +9893,7 @@ func (p *parser) handleIdentifier(loc logger.Loc, assignTarget js_ast.AssignTarg
 	}
 
 	// Warn about uses of "require" other than a direct call
-	if ref == p.requireRef && e != p.callTarget && e != p.typeofTarget && p.fnOrArrowDataVisit.tryBodyCount == 0 {
+	if ref == p.requireRef && e != p.callTarget && e != p.typeofTarget && e != p.cjsDotMainTarget && p.fnOrArrowDataVisit.tryBodyCount == 0 {
 		// "typeof require == 'function' && require"
 		if e == p.typeofRequireEqualsFnTarget {
 			// Become "false" in the browser and "require" in node