automatically mark "RegExp.escape()" calls as pure

evanw · evanw · commit 07aa646bb2fd · 2025-11-01T16:10:21.000-04:00
diff --git a/internal/js_parser/js_parser.go b/internal/js_parser/js_parser.go
@@ -15266,6 +15266,17 @@ func (p *parser) visitExprInOut(expr js_ast.Expr, in exprIn) (js_ast.Expr, exprO
 							}
 						}
 					}
+
+				case "escape":
+					// Recognize "RegExp.escape()" calls
+					if id, ok := t.Target.Data.(*js_ast.EIdentifier); ok {
+						if symbol := &p.symbols[id.Ref.InnerIndex]; symbol.Kind == ast.SymbolUnbound && symbol.OriginalName == "RegExp" {
+							if js_ast.KnownPrimitiveType(e.Args[0].Data) == js_ast.PrimitiveString {
+								// Mark "RegExp.escape" with a string literal as pure
+								e.CanBeUnwrappedIfUnused = true
+							}
+						}
+					}
 				}
 			}
 
diff --git a/internal/js_parser/js_parser_test.go b/internal/js_parser/js_parser_test.go
@@ -6751,6 +6751,18 @@ func TestAutoPureForDate(t *testing.T) {
 	expectPrinted(t, "new Date(foo ? x : y)", "new Date(foo ? x : y);\n")
 }
 
+func TestAutoPureForRegExpEscape(t *testing.T) {
+	expectPrinted(t, "RegExp.escape('x')", "/* @__PURE__ */ RegExp.escape(\"x\");\n")
+	expectPrinted(t, "RegExp.escape(`${x}`)", "/* @__PURE__ */ RegExp.escape(`${x}`);\n")
+	expectPrinted(t, "RegExp.escape(x ? 'y' : 'z')", "/* @__PURE__ */ RegExp.escape(x ? \"y\" : \"z\");\n")
+
+	expectPrinted(t, "RegExp.escape()", "RegExp.escape();\n")
+	expectPrinted(t, "RegExp.escape(x`y`)", "RegExp.escape(x`y`);\n")
+	expectPrinted(t, "RegExp.escape('x', 'y')", "RegExp.escape(\"x\", \"y\");\n")
+	expectPrinted(t, "RegExp.escape(x ? 'y' : z)", "RegExp.escape(x ? \"y\" : z);\n")
+	expectPrinted(t, "RegExp.escape(x ? y : 'z')", "RegExp.escape(x ? y : \"z\");\n")
+}
+
 // See: https://github.com/tc39/proposal-explicit-resource-management
 func TestUsing(t *testing.T) {
 	expectPrinted(t, "using x = y", "using x = y;\n")

Original file line number	Diff line number	Diff line change
`@@ -15266,6 +15266,17 @@ func (p *parser) visitExprInOut(expr js_ast.Expr, in exprIn) (js_ast.Expr, exprO`
`15266`	`15266`	`}`
`15267`	`15267`	`}`
`15268`	`15268`	`}`
	`15269`	`+`
	`15270`	`+ case "escape":`
	`15271`	`+ // Recognize "RegExp.escape()" calls`
	`15272`	`+ if id, ok := t.Target.Data.(*js_ast.EIdentifier); ok {`
	`15273`	`+ if symbol := &p.symbols[id.Ref.InnerIndex]; symbol.Kind == ast.SymbolUnbound && symbol.OriginalName == "RegExp" {`
	`15274`	`+ if js_ast.KnownPrimitiveType(e.Args[0].Data) == js_ast.PrimitiveString {`
	`15275`	`+ // Mark "RegExp.escape" with a string literal as pure`
	`15276`	`+ e.CanBeUnwrappedIfUnused = true`
	`15277`	`+ }`
	`15278`	`+ }`
	`15279`	`+ }`
`15269`	`15280`	`}`
`15270`	`15281`	`}`
`15271`	`15282`