fix #3898: incorrect cyclic tsconfig.json warning

Author: evanw

CHANGELOG.md

@@ -19,6 +19,10 @@
     ./esbuild --version
     ```
 
+* Avoid incorrect cycle warning with `tsconfig.json` multiple inheritance ([#3898](https://github.com/evanw/esbuild/issues/3898))
+
+    TypeScript 5.0 introduced multiple inheritance for `tsconfig.json` files where `extends` can be an array of file paths. Previously esbuild would incorrectly treat files encountered more than once when processing separate subtrees of the multiple inheritance hierarchy as an inheritance cycle. With this release, `tsconfig.json` files containing this edge case should work correctly without generating a warning.
+
 * Handle Yarn Plug'n'Play stack overflow with `tsconfig.json` ([#3915](https://github.com/evanw/esbuild/issues/3915))
 
     Previously a `tsconfig.json` file that `extends` another file in a package with an `exports` map could cause a stack overflow when Yarn's Plug'n'Play resolution was active. This edge case should work now starting with this release.

internal/bundler_tests/bundler_tsconfig_test.go

@@ -2817,3 +2817,55 @@ func TestTsconfigStackOverflowYarnPnP(t *testing.T) {
 		},
 	})
 }
+
+func TestTsconfigJsonExtendsArrayIssue3898(t *testing.T) {
+	tsconfig_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/Users/user/project/index.tsx": `
+				import { type SomeType } from 'MUST_KEEP'
+				console.log(<>
+					<div/>
+				</>)
+			`,
+			"/Users/user/project/tsconfig.json": `
+				{
+					"extends": [
+						"./tsconfigs/a.json",
+						"./tsconfigs/b.json",
+					]
+				}
+			`,
+			"/Users/user/project/tsconfigs/base.json": `
+				{
+					"compilerOptions": {
+						"verbatimModuleSyntax": true,
+					}
+				}
+			`,
+			"/Users/user/project/tsconfigs/a.json": `
+				{
+					"extends": "./base.json",
+					"compilerOptions": {
+						"jsxFactory": "SUCCESS",
+					}
+				}
+			`,
+			"/Users/user/project/tsconfigs/b.json": `
+				{
+					"extends": "./base.json",
+					"compilerOptions": {
+						"jsxFragmentFactory": "WORKS",
+					}
+				}
+			`,
+		},
+		entryPaths: []string{"/Users/user/project/index.tsx"},
+		options: config.Options{
+			Mode:          config.ModePassThrough,
+			AbsOutputFile: "/Users/user/project/out.js",
+			JSX: config.JSXOptions{
+				SideEffects: true,
+			},
+		},
+	})
+}

internal/bundler_tests/snapshots/snapshots_tsconfig.txt

@@ -290,6 +290,12 @@ TestTsconfigJsonExtendsAbsolute
 // Users/user/project/entry.jsx
 console.log(/* @__PURE__ */ baseFactory("div", null), /* @__PURE__ */ baseFactory(derivedFragment, null));
 
+================================================================================
+TestTsconfigJsonExtendsArrayIssue3898
+---------- /Users/user/project/out.js ----------
+import {} from "MUST_KEEP";
+console.log(SUCCESS(WORKS, null, SUCCESS("div", null)));
+
 ================================================================================
 TestTsconfigJsonExtendsLoop
 ---------- /out.js ----------

internal/resolver/resolver.go

@@ -1183,11 +1183,6 @@ func (r resolverQuery) parseTSConfig(file string, visited map[string]bool, confi
 	if visited[file] {
 		return nil, errParseErrorImportCycle
 	}
-	if visited != nil {
-		// This is only non-nil for "build" API calls. This is nil for "transform"
-		// API calls, which tells us to not process "extends" fields.
-		visited[file] = true
-	}
 
 	contents, err, originalError := r.caches.FSCache.ReadFile(r.fs, file)
 	if r.debugLogs != nil && originalError != nil {
@@ -1206,7 +1201,20 @@ func (r resolverQuery) parseTSConfig(file string, visited map[string]bool, confi
 		PrettyPath: PrettyPath(r.fs, keyPath),
 		Contents:   contents,
 	}
-	return r.parseTSConfigFromSource(source, visited, configDir)
+	if visited != nil {
+		// This is only non-nil for "build" API calls. This is nil for "transform"
+		// API calls, which tells us to not process "extends" fields.
+		visited[file] = true
+	}
+	result, err := r.parseTSConfigFromSource(source, visited, configDir)
+	if visited != nil {
+		// Reset this to back false in case something uses TypeScript 5.0's multiple
+		// inheritance feature for "tsconfig.json" files. It should be valid to visit
+		// the same base "tsconfig.json" file multiple times from different multiple
+		// inheritance subtrees.
+		visited[file] = false
+	}
+	return result, err
 }
 
 func (r resolverQuery) parseTSConfigFromSource(source logger.Source, visited map[string]bool, configDir string) (*TSConfigJSON, error) {