calling Symbol.for with a primitive never throws

Author: evanw

internal/bundler_tests/bundler_dce_test.go

@@ -4977,3 +4977,33 @@ func TestDCEOfSymbolCtorCall(t *testing.T) {
 		},
 	})
 }
+
+func TestDCEOfSymbolForCall(t *testing.T) {
+	dce_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.js": `
+				const y0 = Symbol.for(undefined)
+				const y1 = Symbol.for(null)
+				const y2 = Symbol.for(true)
+				const y3 = Symbol.for(123)
+				const y4 = Symbol.for(123n)
+				const y5 = Symbol.for('abc')
+				const y6 = Symbol.for(/* @__PURE__ */ (() => Math.random() < 0.5)() ? 'x' : 'y')
+
+				const n0 = Symbol.for()
+				const n1 = Symbol.for({})
+				const n2 = Symbol.for(/./)
+				const n3 = Symbol.for(() => 0)
+				const n4 = Symbol.for(x)
+				const n5 = new Symbol.for('abc')
+				const n6 = Symbol.for(1, 2, 3)
+				const n7 = Symbol.for((() => Math.random() < 0.5)() ? 'x' : 'y')
+			`,
+		},
+		entryPaths: []string{"/entry.js"},
+		options: config.Options{
+			Mode:          config.ModeBundle,
+			AbsOutputFile: "/out.js",
+		},
+	})
+}

internal/bundler_tests/snapshots/snapshots_dce.txt

@@ -675,6 +675,19 @@ var n4 = new Symbol("abc");
 var n5 = Symbol(1, 2, 3);
 var n6 = /* @__PURE__ */ Symbol((() => Math.random() < 0.5)() ? "x" : "y");
 
+================================================================================
+TestDCEOfSymbolForCall
+---------- /out.js ----------
+// entry.js
+var n0 = Symbol.for();
+var n1 = Symbol.for({});
+var n2 = Symbol.for(/./);
+var n3 = Symbol.for(() => 0);
+var n4 = Symbol.for(x);
+var n5 = new Symbol.for("abc");
+var n6 = Symbol.for(1, 2, 3);
+var n7 = /* @__PURE__ */ Symbol.for((() => Math.random() < 0.5)() ? "x" : "y");
+
 ================================================================================
 TestDCEOfSymbolInstances
 ---------- /out/class.js ----------

internal/js_parser/js_parser.go

@@ -15266,6 +15266,16 @@ func (p *parser) visitExprInOut(expr js_ast.Expr, in exprIn) (js_ast.Expr, exprO
 						}
 					}
 
+				case "for":
+					// Calling "Symbol.for()" with a primitive will never throw
+					if id, ok := t.Target.Data.(*js_ast.EIdentifier); ok {
+						if symbol := &p.symbols[id.Ref.InnerIndex]; symbol.Kind == ast.SymbolUnbound && symbol.OriginalName == "Symbol" {
+							if js_ast.KnownPrimitiveType(e.Args[0].Data) != js_ast.PrimitiveUnknown {
+								e.CanBeUnwrappedIfUnused = true
+							}
+						}
+					}
+
 				case "create":
 					// Recognize "Object.create()" calls
 					if id, ok := t.Target.Data.(*js_ast.EIdentifier); ok {

scripts/decorator-tests.js

@@ -1,7 +1,7 @@
 var __create = Object.create;
 var __defProp = Object.defineProperty;
 var __getOwnPropDesc = Object.getOwnPropertyDescriptor;
-var __knownSymbol = (name, symbol) => (symbol = Symbol[name]) ? symbol : Symbol.for("Symbol." + name);
+var __knownSymbol = (name, symbol) => (symbol = Symbol[name]) ? symbol : /* @__PURE__ */ Symbol.for("Symbol." + name);
 var __typeError = (msg) => {
   throw TypeError(msg);
 };