bundler: gate @bun pragma and @bun-cjs wrapper on build target, not entry hashbang

src/bundler/linker_context/postProcessJSChunk.rs

@@ -515,7 +515,13 @@ pub fn post_process_js_chunk(
     }
 
     // Add @bun comments and CJS wrapper start for each chunk when targeting Bun.
-    let is_bun = c.graph.ast.items_target()[chunk.entry_point.source_index() as usize].is_bun();
+    // The pragma promises Latin-1-safe bytes for the whole chunk, so gate on
+    // every signal that any part was printed without ASCII-only escaping.
+    let is_bun = c.options.target.is_bun()
+        && c.graph.ast.items_target()[chunk.entry_point.source_index() as usize].is_bun()
+        && !chunk
+            .flags
+            .contains(crate::chunk::Flags::IS_BROWSER_CHUNK_FROM_SERVER_BUILD);
     if is_bun {
         if c.options.generate_bytecode_cache && output_format == options::OutputFormat::Cjs {
             const INPUT: &[u8] =

test/bundler/bundler_bun.test.ts

@@ -137,6 +137,64 @@ error: Hello World`,
     },
     run: { stdout: "" },
   });
+  for (const target of ["node", "browser"] as const) {
+    itBundled(`bun/HashbangBunNoPragmaFor_${target}`, {
+      target,
+      files: {
+        "/entry.ts": `#!/usr/bin/env bun\nimport { Café } from "./lib.ts";\nconsole.log(new Café().méth());\n`,
+        "/lib.ts": `export class Café { méth() { return 7 } }\n`,
+      },
+      onAfterBundle(api) {
+        const out = api.readFile("/out.js");
+        expect(out).toStartWith("#!/usr/bin/env bun\n");
+        expect(out).not.toContain("// @bun");
+      },
+      run: { stdout: "7" },
+    });
+  }
+  itBundled("bun/HashbangBunPragmaForBunTarget", {
+    target: "bun",
+    files: {
+      "/entry.ts": `#!/usr/bin/env bun\nimport { Café } from "./lib.ts";\nconsole.log(new Café().méth());\n`,
+      "/lib.ts": `export class Café { méth() { return 7 } }\n`,
+    },
+    onAfterBundle(api) {
+      const out = api.readFile("/out.js");
+      expect(out).toStartWith("#!/usr/bin/env bun\n// @bun\n");
+      expect(out).not.toContain("méth");
+    },
+    run: { stdout: "7" },
+  });
+  for (const target of ["node", "browser"] as const) {
+    itBundled(`bun/HashbangBunNoCjsWrapperFor_${target}`, {
+      target,
+      format: "cjs",
+      files: {
+        "/entry.ts": `#!/usr/bin/env bun\nconsole.log("ALIVE", 42);\n`,
+      },
+      onAfterBundle(api) {
+        const out = api.readFile("/out.js");
+        expect(out).toStartWith("#!/usr/bin/env bun\n");
+        expect(out).not.toContain("@bun");
+        expect(out).not.toContain("(function(exports, require, module, __filename, __dirname)");
+      },
+      run: target === "node" ? { runtime: "node", stdout: "ALIVE 42" } : undefined,
+    });
+  }
+  itBundled("bun/HashbangBunCjsWrapperForBunTarget", {
+    target: "bun",
+    format: "cjs",
+    files: {
+      "/entry.ts": `#!/usr/bin/env bun\nconsole.log("ALIVE", 42);\n`,
+    },
+    onAfterBundle(api) {
+      const out = api.readFile("/out.js");
+      expect(out).toStartWith(
+        "#!/usr/bin/env bun\n// @bun @bun-cjs\n(function(exports, require, module, __filename, __dirname) {",
+      );
+    },
+    run: { stdout: "ALIVE 42" },
+  });
   if (Bun.version.startsWith("1.4") || Bun.version.startsWith("1.3") || Bun.version.startsWith("1.2")) {
     for (const backend of ["api", "cli"] as const) {
       itBundled("bun/ExportsConditionsDevelopment" + backend.toUpperCase(), {