fix #3033: mapped type parameters can be keywords

evanw · Apr 1, 2023 · 9fbf1fd · 9fbf1fd
1 parent b2b8978
commit 9fbf1fd
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Showing 3 changed files with 23 additions and 2 deletions.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,5 +1,18 @@
 # Changelog
 
+## Unreleased
+
+* Allow keywords as type parameter names in mapped types ([#3033](https://github.com/evanw/esbuild/issues/3033))
+
+    TypeScript allows type keywords to be used as parameter names in mapped types. Previously esbuild incorrectly treated this as an error. Code that does this is now supported:
+
+    ```ts
+    type Foo = 'a' | 'b' | 'c'
+    type A = { [keyof in Foo]: number }
+    type B = { [infer in Foo]: number }
+    type C = { [readonly in Foo]: number }
+    ```
+
 ## 0.17.14
 
 * Allow the TypeScript 5.0 `const` modifier in object type declarations ([#3021](https://github.com/evanw/esbuild/issues/3021))

diff --git a/internal/js_parser/ts_parser.go b/internal/js_parser/ts_parser.go
@@ -314,11 +314,12 @@ loop:
 				// Valid:
 				//   "[keyof: string]"
 				//   "{[keyof: string]: number}"
+				//   "{[keyof in string]: number}"
 				//
 				// Invalid:
 				//   "A extends B ? keyof : string"
 				//
-				if p.lexer.Token != js_lexer.TColon || (!flags.has(isIndexSignatureFlag) && !flags.has(allowTupleLabelsFlag)) {
+				if (p.lexer.Token != js_lexer.TColon && p.lexer.Token != js_lexer.TIn) || (!flags.has(isIndexSignatureFlag) && !flags.has(allowTupleLabelsFlag)) {
 					p.skipTypeScriptType(js_ast.LPrefix)
 				}
 				break loop
@@ -329,7 +330,8 @@ loop:
 				// "type Foo = Bar extends [infer T] ? T : null"
 				// "type Foo = Bar extends [infer T extends string] ? T : null"
 				// "type Foo = Bar extends [infer T extends string ? infer T : never] ? T : null"
-				if p.lexer.Token != js_lexer.TColon || (!flags.has(isIndexSignatureFlag) && !flags.has(allowTupleLabelsFlag)) {
+				// "type Foo = { [infer in Bar]: number }"
+				if (p.lexer.Token != js_lexer.TColon && p.lexer.Token != js_lexer.TIn) || (!flags.has(isIndexSignatureFlag) && !flags.has(allowTupleLabelsFlag)) {
 					p.lexer.Expect(js_lexer.TIdentifier)
 					if p.lexer.Token == js_lexer.TExtends {
 						p.trySkipTypeScriptConstraintOfInferTypeWithBacktracking(flags)

diff --git a/internal/js_parser/ts_parser_test.go b/internal/js_parser/ts_parser_test.go
@@ -158,6 +158,12 @@ func TestTSTypes(t *testing.T) {
 	expectPrintedTS(t, "type Foo<T> = {readonly [P in keyof T]: T[P]}", "")
 	expectPrintedTS(t, "type Foo<T> = {-readonly [P in keyof T]: T[P]}", "")
 	expectPrintedTS(t, "type Foo<T> = {+readonly [P in keyof T]: T[P]}", "")
+	expectPrintedTS(t, "type Foo<T> = {[infer in T]?: Foo}", "")
+	expectPrintedTS(t, "type Foo<T> = {[keyof in T]?: Foo}", "")
+	expectPrintedTS(t, "type Foo<T> = {[asserts in T]?: Foo}", "")
+	expectPrintedTS(t, "type Foo<T> = {[abstract in T]?: Foo}", "")
+	expectPrintedTS(t, "type Foo<T> = {[readonly in T]?: Foo}", "")
+	expectPrintedTS(t, "type Foo<T> = {[satisfies in T]?: Foo}", "")
 	expectPrintedTS(t, "let x: number! = y", "let x = y;\n")
 	expectPrintedTS(t, "let x: number \n !y", "let x;\n!y;\n")
 	expectPrintedTS(t, "const x: unique = y", "const x = y;\n")