fix #3161: panic when minifying static {}

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+* Fix a panic due to empty static class blocks ([#3161](https://github.com/evanw/esbuild/issues/3161))
+
+    This release fixes a bug where an internal invariant that was introduced in the previous release was sometimes violated, which then caused a panic. It happened when bundling code containing an empty static class block with both minification and bundling enabled.
+
 ## 0.18.2
 
 * Lower static blocks when static fields are lowered ([#2800](https://github.com/evanw/esbuild/issues/2800), [#2950](https://github.com/evanw/esbuild/issues/2950), [#3025](https://github.com/evanw/esbuild/issues/3025))

internal/bundler_tests/bundler_dce_test.go

@@ -2118,6 +2118,52 @@ func TestDCEClassStaticBlocks(t *testing.T) {
 	})
 }
 
+func TestDCEClassStaticBlocksMinifySyntax(t *testing.T) {
+	dce_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.ts": `
+				class A_REMOVE {
+					static {}
+				}
+				class B_REMOVE {
+					static { 123 }
+				}
+				class C_REMOVE {
+					static { /* @__PURE__*/ foo() }
+				}
+				class D_REMOVE {
+					static { try {} catch {} }
+				}
+				class E_REMOVE {
+					static { try { /* @__PURE__*/ foo() } catch {} }
+				}
+				class F_REMOVE {
+					static { try { 123 } catch { 123 } finally { 123 } }
+				}
+
+				class A_keep {
+					static { foo }
+				}
+				class B_keep {
+					static { this.foo }
+				}
+				class C_keep {
+					static { try { foo } catch {} }
+				}
+				class D_keep {
+					static { try {} finally { foo } }
+				}
+			`,
+		},
+		entryPaths: []string{"/entry.js"},
+		options: config.Options{
+			Mode:          config.ModeBundle,
+			AbsOutputFile: "/out.js",
+			MinifySyntax:  true,
+		},
+	})
+}
+
 func TestDCEVarExports(t *testing.T) {
 	dce_suite.expectBundled(t, bundled{
 		files: map[string]string{

internal/bundler_tests/snapshots/snapshots_dce.txt

@@ -363,6 +363,33 @@ var D_keep = class {
   }
 })();
 
+================================================================================
+TestDCEClassStaticBlocksMinifySyntax
+---------- /out.js ----------
+// entry.ts
+var A_keep = class {
+};
+foo;
+var _B_keep = class {
+}, B_keep = _B_keep;
+_B_keep.foo;
+var C_keep = class {
+};
+(() => {
+  try {
+    foo;
+  } catch {
+  }
+})();
+var D_keep = class {
+};
+(() => {
+  try {
+  } finally {
+    foo;
+  }
+})();
+
 ================================================================================
 TestDCEOfIIFE
 ---------- /out/remove-these.js ----------

internal/js_parser/js_parser.go

@@ -10989,8 +10989,6 @@ func (p *parser) visitClass(nameScopeLoc logger.Loc, class *js_ast.Class, defaul
 	// A scope is needed for private identifiers
 	p.pushScopeForVisitPass(js_ast.ScopeClassBody, class.BodyLoc)
 
-	end := 0
-
 	for i := range class.Properties {
 		property := &class.Properties[i]
 
@@ -11022,15 +11020,6 @@ func (p *parser) visitClass(nameScopeLoc logger.Loc, class *js_ast.Class, defaul
 
 			p.fnOrArrowDataVisit = oldFnOrArrowData
 			p.fnOnlyDataVisit = oldFnOnlyDataVisit
-
-			// "class { static {} }" => "class {}"
-			if p.options.minifySyntax && len(property.ClassStaticBlock.Block.Stmts) == 0 {
-				continue
-			}
-
-			// Keep this property
-			class.Properties[end] = *property
-			end++
 			continue
 		}
 
@@ -11158,15 +11147,8 @@ func (p *parser) visitClass(nameScopeLoc logger.Loc, class *js_ast.Class, defaul
 
 		// Restore the ability to use "arguments" in decorators and computed properties
 		p.currentScope.ForbidArguments = false
-
-		// Keep this property
-		class.Properties[end] = *property
-		end++
 	}
 
-	// Finish the filtering operation
-	class.Properties = class.Properties[:end]
-
 	// Analyze side effects before adding the name keeping call
 	result.canBeRemovedIfUnused = js_ast.ClassCanBeRemovedIfUnused(*class, p.isUnbound)
 

internal/js_parser/js_parser_lower.go

@@ -2047,7 +2047,7 @@ func (p *parser) computeClassLoweringInfo(class *js_ast.Class) (result classLowe
 		}
 
 		if prop.Kind == js_ast.PropertyClassStaticBlock {
-			if p.options.unsupportedJSFeatures.Has(compat.ClassStaticBlocks) && len(prop.ClassStaticBlock.Block.Stmts) > 0 {
+			if p.options.unsupportedJSFeatures.Has(compat.ClassStaticBlocks) {
 				result.lowerAllStaticFields = true
 			}
 			continue
@@ -2306,6 +2306,11 @@ func (p *parser) lowerClass(stmt js_ast.Stmt, expr js_ast.Expr, result visitClas
 
 	for _, prop := range class.Properties {
 		if prop.Kind == js_ast.PropertyClassStaticBlock {
+			// Drop empty class blocks when minifying
+			if p.options.minifySyntax && len(prop.ClassStaticBlock.Block.Stmts) == 0 {
+				continue
+			}
+
 			if classLoweringInfo.lowerAllStaticFields {
 				block := *prop.ClassStaticBlock
 				isAllExprs := []js_ast.Expr{}

internal/js_parser/js_parser_lower_test.go

@@ -529,6 +529,18 @@ func TestLowerClassStaticThis(t *testing.T) {
 		"var _a;\nx = (_a = class {\n}, __publicField(_a, \"x\", class extends _a {\n}), _a);\n")
 }
 
+func TestLowerClassStaticBlocks(t *testing.T) {
+	expectPrintedTarget(t, 2015, "class Foo { static {} }", "class Foo {\n}\n")
+	expectPrintedTarget(t, 2015, "class Foo { static {} x() {} }", "class Foo {\n  x() {\n  }\n}\n")
+	expectPrintedTarget(t, 2015, "class Foo { x() {} static {} }", "class Foo {\n  x() {\n  }\n}\n")
+	expectPrintedTarget(t, 2015, "class Foo { static { x } static {} static { y } }", "class Foo {\n}\nx;\ny;\n")
+
+	expectPrintedMangleTarget(t, 2015, "class Foo { static {} }", "class Foo {\n}\n")
+	expectPrintedMangleTarget(t, 2015, "class Foo { static {} x() {} }", "class Foo {\n  x() {\n  }\n}\n")
+	expectPrintedMangleTarget(t, 2015, "class Foo { x() {} static {} }", "class Foo {\n  x() {\n  }\n}\n")
+	expectPrintedMangleTarget(t, 2015, "class Foo { static { x } static {} static { y } }", "class Foo {\n}\nx, y;\n")
+}
+
 func TestLowerOptionalChain(t *testing.T) {
 	expectPrintedTarget(t, 2019, "a?.b.c", "a == null ? void 0 : a.b.c;\n")
 	expectPrintedTarget(t, 2019, "(a?.b).c", "(a == null ? void 0 : a.b).c;\n")

internal/js_parser/js_parser_test.go

@@ -1935,6 +1935,11 @@ func TestClassStaticBlocks(t *testing.T) {
 	expectParseError(t, "class Foo { static { continue } }", "<stdin>: ERROR: Cannot use \"continue\" here:\n")
 	expectParseError(t, "x: { class Foo { static { break x } } }", "<stdin>: ERROR: There is no containing label named \"x\"\n")
 	expectParseError(t, "x: { class Foo { static { continue x } } }", "<stdin>: ERROR: There is no containing label named \"x\"\n")
+
+	expectPrintedMangle(t, "class Foo { static {} }", "class Foo {\n}\n")
+	expectPrintedMangle(t, "class Foo { static { 123 } }", "class Foo {\n}\n")
+	expectPrintedMangle(t, "class Foo { static { /* @__PURE__ */ foo() } }", "class Foo {\n}\n")
+	expectPrintedMangle(t, "class Foo { static { foo() } }", "class Foo {\n  static {\n    foo();\n  }\n}\n")
 }
 
 func TestGenerator(t *testing.T) {

scripts/js-api-tests.js

@@ -6485,6 +6485,12 @@ class Foo {
     assert.strictEqual(fromPromiseResolve(code4), `Promise.resolve().then(function(){return __toESM(require(foo))});\n`)
   },
 
+  async classStaticBlocks({ esbuild }) {
+    // Check that empty static class blocks are still lowered (this was a regression in version 0.18.2)
+    assert.strictEqual((await esbuild.transform(`class Foo { static {} }`, { supported: { 'class-static-blocks': false } })).code, `class Foo {\n}\n`)
+    assert.strictEqual((await esbuild.transform(`class Foo { static { x } }`, { supported: { 'class-static-blocks': false } })).code, `class Foo {\n}\nx;\n`)
+  },
+
   async inlineScript({ esbuild }) {
     let p
     assert.strictEqual((await esbuild.transform(`x = '</script>'`, {})).code, `x = "<\\/script>";\n`)