fix #4224: allow try statements to become dead

Author: evanw

CHANGELOG.md

@@ -281,6 +281,22 @@
     }
     ```
 
+* Improve tree-shaking of `try` statements in dead code ([#4224](https://github.com/evanw/esbuild/issues/4224))
+
+    With this release, esbuild will now remove certain `try` statements if esbuild considers them to be within dead code (i.e. code that is known to not ever be evaluated). For example:
+
+    ```js
+    // Original code
+    return 'foo'
+    try { return 'bar' } catch {}
+
+    // Old output (with --minify)
+    return"foo";try{return"bar"}catch{}
+
+    // New output (with --minify)
+    return"foo";
+    ```
+
 * Update Go from 1.23.5 to 1.23.7 ([#4076](https://github.com/evanw/esbuild/issues/4076), [#4077](https://github.com/evanw/esbuild/pull/4077))
 
     This should have no effect on existing code as this version change does not change Go's operating system support. It may remove certain reports from vulnerability scanners that detect which version of the Go compiler esbuild uses.

internal/js_parser/js_parser.go

@@ -8614,6 +8614,15 @@ func findIdentifiers(binding js_ast.Binding, identifiers []js_ast.Decl) []js_ast
 	return identifiers
 }
 
+func shouldKeepStmtsInDeadControlFlow(stmts []js_ast.Stmt) bool {
+	for _, child := range stmts {
+		if shouldKeepStmtInDeadControlFlow(child) {
+			return true
+		}
+	}
+	return false
+}
+
 // If this is in a dead branch, then we want to trim as much dead code as we
 // can. Everything can be trimmed except for hoisted declarations ("var" and
 // "function"), which affect the parent scope. For example:
@@ -8650,12 +8659,12 @@ func shouldKeepStmtInDeadControlFlow(stmt js_ast.Stmt) bool {
 		return true
 
 	case *js_ast.SBlock:
-		for _, child := range s.Stmts {
-			if shouldKeepStmtInDeadControlFlow(child) {
-				return true
-			}
-		}
-		return false
+		return shouldKeepStmtsInDeadControlFlow(s.Stmts)
+
+	case *js_ast.STry:
+		return shouldKeepStmtsInDeadControlFlow(s.Block.Stmts) ||
+			(s.Catch != nil && shouldKeepStmtsInDeadControlFlow(s.Catch.Block.Stmts)) ||
+			(s.Finally != nil && shouldKeepStmtsInDeadControlFlow(s.Finally.Block.Stmts))
 
 	case *js_ast.SIf:
 		return shouldKeepStmtInDeadControlFlow(s.Yes) || (s.NoOrNil.Data != nil && shouldKeepStmtInDeadControlFlow(s.NoOrNil))

internal/js_parser/js_parser_test.go

@@ -5429,6 +5429,24 @@ func TestTrimCodeInDeadControlFlow(t *testing.T) {
 	expectPrintedMangle(t, "if (1) a(); else { for(;;){var a} }", "if (1) a();\nelse\n  for (; ; )\n    var a;\n")
 	expectPrintedMangle(t, "if (1) { a(); b() } else { var a; var b; }", "if (1)\n  a(), b();\nelse\n  var a, b;\n")
 	expectPrintedMangle(t, "if (1) a(); else { switch (1) { case 1: case 2: var a } }", "if (1) a();\nelse\n  var a;\n")
+
+	// See: https://github.com/evanw/esbuild/issues/4224
+	expectPrintedMangle(t, "return 'foo'; try { return 'bar' } catch {}", "return \"foo\";\n")
+	expectPrintedMangle(t, "return foo = true; try { var foo } catch {}", "return foo = true;\ntry {\n  var foo;\n} catch {\n}\n")
+	expectPrintedMangle(t, "return foo = true; try {} catch { var foo }", "return foo = true;\ntry {\n} catch {\n  var foo;\n}\n")
+	expectPrintedMangle(t, `
+		async function test() {
+			if (true) return { status: "disabled_for_development" };
+			try {
+				const response = await httpClients.releasesApi.get();
+				if (!response.ok) return { status: "no_release_found" };
+				if (response.statusCode === 204) return { status: "up_to_date" };
+			} catch (error) {
+				return { status: "no_release_found" };
+			}
+			return { status: "downloading" };
+		}
+	`, "async function test() {\n  return { status: \"disabled_for_development\" };\n}\n")
 }
 
 func TestPreservedComments(t *testing.T) {