fix #1976: parse "super()" with "--mangle-props=."

Author: evanw

CHANGELOG.md

@@ -1,5 +1,24 @@
 # Changelog
 
+## Unreleased
+
+* Avoid a syntax error due to `--mangle-props=.` and `super()` ([#1976](https://github.com/evanw/esbuild/issues/1976))
+
+    This release fixes an issue where passing `--mangle-props=.` (i.e. telling esbuild to mangle every single property) caused a syntax error with code like this:
+
+    ```js
+    class Foo {}
+    class Bar extends Foo {
+      constructor() {
+        super();
+      }
+    }
+    ```
+
+    The problem was that `constructor` was being renamed to another method, which then made it no longer a constructor, which meant that `super()` was now a syntax error. I have added a workaround that avoids renaming any property named `constructor` so that esbuild doesn't generate a syntax error here.
+
+    Despite this fix, I highly recommend not using `--mangle-props=.` because your code will almost certainly be broken. You will have to manually add every single property that you don't want mangled to `--reserve-props=` which is an excessive maintenance burden (e.g. reserve `parse` to use `JSON.parse`). Instead I recommend using a common pattern for all properties you intend to be mangled that is unlikely to appear in the APIs you use such as "ends in an underscore." This is an opt-in approach instead of an opt-out approach. It also makes it obvious when reading the code which properties will be mangled and which ones won't be.
+
 ## 0.14.16
 
 * Support property name mangling with some TypeScript syntax features

internal/bundler/bundler_default_test.go

@@ -5826,3 +5826,28 @@ func TestManglePropsLoweredClassFields(t *testing.T) {
 		},
 	})
 }
+
+// This tests for a case where "constructor" was being mangled, which made the
+// method become a non-constructor, and then "super()" caused a parse error.
+// The fix was to prevent the property "constructor" from being mangled.
+// See: https://github.com/evanw/esbuild/issues/1976
+func TestManglePropsSuperCall(t *testing.T) {
+	loader_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.js": `
+				class Foo {}
+				class Bar extends Foo {
+					constructor() {
+						super();
+					}
+				}
+			`,
+		},
+		entryPaths: []string{"/entry.js"},
+		options: config.Options{
+			Mode:          config.ModePassThrough,
+			AbsOutputFile: "/out.js",
+			MangleProps:   regexp.MustCompile("."),
+		},
+	})
+}

internal/bundler/snapshots/snapshots_loader.txt

@@ -691,6 +691,17 @@ TestManglePropsShorthand
 ---------- /out.js ----------
 export let yyyyy = ({ y }) => ({ y });
 
+================================================================================
+TestManglePropsSuperCall
+---------- /out.js ----------
+class Foo {
+}
+class Bar extends Foo {
+  constructor() {
+    super();
+  }
+}
+
 ================================================================================
 TestManglePropsTypeScriptFeatures
 ---------- /out/parameter-properties.js ----------

internal/js_parser/js_parser.go

@@ -2480,11 +2480,25 @@ func (p *parser) parsePropertyBinding() js_ast.PropertyBinding {
 	}
 }
 
+// These properties have special semantics in JavaScript. They must not be
+// mangled or we could potentially fail to parse valid JavaScript syntax or
+// generate invalid JavaScript syntax as output.
+//
+// This list is only intended to contain properties specific to the JavaScript
+// language itself to avoid syntax errors in the generated output. It's not
+// intended to contain properties for JavaScript APIs. Those must be provided
+// by the user.
+var permanentReservedProps = map[string]bool{
+	"__proto__":   true,
+	"constructor": true,
+	"prototype":   true,
+}
+
 func (p *parser) isMangledProp(name string) bool {
 	if p.options.mangleProps == nil {
 		return false
 	}
-	if p.options.mangleProps.MatchString(name) && name != "__proto__" && (p.options.reserveProps == nil || !p.options.reserveProps.MatchString(name)) {
+	if p.options.mangleProps.MatchString(name) && !permanentReservedProps[name] && (p.options.reserveProps == nil || !p.options.reserveProps.MatchString(name)) {
 		return true
 	}
 	reservedProps := p.reservedProps