fix(transpiler): ignore @__PURE__ annotations during runtime execution

@__PURE__ / #__PURE__ annotations are hints for bundlers and tree-shakers
to indicate that a call expression has no side effects and can be removed
if its result is unused. These annotations should only affect bundling,
not runtime execution.

Previously, when running `bun run file.js`, the transpiler would honor
@__PURE__ annotations and strip annotated call expressions, causing
unexpected behavior like `process.exit(0)` being silently removed.

Set `ignore_dce_annotations = true` in:
- Runtime execution paths (bun run, standalone)
- Test runner (bun test)
- Non-bundle build mode (bun build --no-bundle)

Bundler mode (bun build) continues to respect @__PURE__ annotations.

Closes #19355

Co-Authored-By: Claude <noreply@anthropic.com>

src/bun.js.zig

@@ -63,7 +63,10 @@ pub const Run = struct {
 
         b.options.minify_identifiers = ctx.bundler_options.minify_identifiers;
         b.options.minify_whitespace = ctx.bundler_options.minify_whitespace;
-        b.options.ignore_dce_annotations = ctx.bundler_options.ignore_dce_annotations;
+        // @__PURE__ annotations are hints for bundlers/tree-shakers and should
+        // not cause code removal during runtime execution.
+        // See: https://github.com/oven-sh/bun/issues/19355
+        b.options.ignore_dce_annotations = true;
         b.resolver.opts.minify_identifiers = ctx.bundler_options.minify_identifiers;
         b.resolver.opts.minify_whitespace = ctx.bundler_options.minify_whitespace;
 
@@ -222,7 +225,10 @@ pub const Run = struct {
 
         b.options.minify_identifiers = ctx.bundler_options.minify_identifiers;
         b.options.minify_whitespace = ctx.bundler_options.minify_whitespace;
-        b.options.ignore_dce_annotations = ctx.bundler_options.ignore_dce_annotations;
+        // @__PURE__ annotations are hints for bundlers/tree-shakers and should
+        // not cause code removal during runtime execution.
+        // See: https://github.com/oven-sh/bun/issues/19355
+        b.options.ignore_dce_annotations = true;
         b.resolver.opts.minify_identifiers = ctx.bundler_options.minify_identifiers;
         b.resolver.opts.minify_whitespace = ctx.bundler_options.minify_whitespace;
 

src/cli/build_command.zig

@@ -78,7 +78,10 @@ pub const BuildCommand = struct {
         this_transpiler.options.minify_identifiers = ctx.bundler_options.minify_identifiers;
         this_transpiler.options.keep_names = ctx.bundler_options.keep_names;
         this_transpiler.options.emit_dce_annotations = ctx.bundler_options.emit_dce_annotations;
-        this_transpiler.options.ignore_dce_annotations = ctx.bundler_options.ignore_dce_annotations;
+        // When not bundling (--no-bundle), @__PURE__ annotations should be
+        // ignored since they are bundler tree-shaking hints.
+        // See: https://github.com/oven-sh/bun/issues/19355
+        this_transpiler.options.ignore_dce_annotations = ctx.bundler_options.ignore_dce_annotations or ctx.bundler_options.transform_only;
 
         this_transpiler.options.banner = ctx.bundler_options.banner;
         this_transpiler.options.footer = ctx.bundler_options.footer;

src/cli/test_command.zig

@@ -1419,6 +1419,10 @@ pub const TestCommand = struct {
         vm.preload = ctx.preloads;
         vm.transpiler.options.rewrite_jest_for_tests = true;
         vm.transpiler.options.env.behavior = .load_all_without_inlining;
+        // @__PURE__ annotations are hints for bundlers/tree-shakers and should
+        // not cause code removal during runtime execution (including tests).
+        // See: https://github.com/oven-sh/bun/issues/19355
+        vm.transpiler.options.ignore_dce_annotations = true;
 
         const node_env_entry = try env_loader.map.getOrPutWithoutValue("NODE_ENV");
         if (!node_env_entry.found_existing) {

test/regression/issue/19355.test.ts

@@ -0,0 +1,83 @@
+import { expect, test } from "bun:test";
+import { bunEnv, bunExe, tempDir } from "harness";
+
+// https://github.com/oven-sh/bun/issues/19355
+// @__PURE__ annotations inside line comments should not cause
+// the next call expression to be removed during runtime execution.
+// @__PURE__ is a bundler tree-shaking hint, not a runtime directive.
+
+test("@__PURE__ inside line comment does not strip next call", async () => {
+  await using proc = Bun.spawn({
+    cmd: [bunExe(), "-e", `// /* @__PURE__ */\n//\nprocess.exit(0);\nconsole.log("hiii");`],
+    env: bunEnv,
+    stdout: "pipe",
+    stderr: "pipe",
+  });
+
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+  expect(stdout).toBe("");
+  expect(exitCode).toBe(0);
+});
+
+test("// @__PURE__ does not strip next call at runtime", async () => {
+  await using proc = Bun.spawn({
+    cmd: [bunExe(), "-e", `// @__PURE__\nprocess.exit(0);\nconsole.log("hiii");`],
+    env: bunEnv,
+    stdout: "pipe",
+    stderr: "pipe",
+  });
+
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+  expect(stdout).toBe("");
+  expect(exitCode).toBe(0);
+});
+
+test("// #__PURE__ does not strip next call at runtime", async () => {
+  await using proc = Bun.spawn({
+    cmd: [bunExe(), "-e", `// #__PURE__\nprocess.exit(0);\nconsole.log("hiii");`],
+    env: bunEnv,
+    stdout: "pipe",
+    stderr: "pipe",
+  });
+
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+  expect(stdout).toBe("");
+  expect(exitCode).toBe(0);
+});
+
+test("/* @__PURE__ */ does not strip next call at runtime", async () => {
+  await using proc = Bun.spawn({
+    cmd: [bunExe(), "-e", `/* @__PURE__ */ process.exit(0);\nconsole.log("hiii");`],
+    env: bunEnv,
+    stdout: "pipe",
+    stderr: "pipe",
+  });
+
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+  expect(stdout).toBe("");
+  expect(exitCode).toBe(0);
+});
+
+test("@__PURE__ is ignored in --no-bundle mode", async () => {
+  const dir = tempDir("pure-no-bundle", {
+    "index.js": `// @__PURE__\nconsole.log("hello");\nconsole.log("world");`,
+  });
+
+  await using proc = Bun.spawn({
+    cmd: [bunExe(), "build", "--no-bundle", dir + "/index.js"],
+    env: bunEnv,
+    stdout: "pipe",
+    stderr: "pipe",
+  });
+
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+  // With --no-bundle, @__PURE__ should be ignored (not strip the call)
+  expect(stdout).toContain("hello");
+  expect(stdout).toContain("world");
+  expect(exitCode).toBe(0);
+});