`deadCodeElimination` toggle for Bun.Transpiler (#5932)

* add Bun.Transpiler DCE option

* mark DCE toggle experimental + tests

* full (hopefully) DCE toggle

* update DCE toggle tests

* add DCE option to types

* run fmt

* Removed uws submodule

1 files changed, 24 insertions, 0 deletions

diff --git a/test/transpiler/transpiler.test.js b/test/transpiler/transpiler.test.js
index a6c2dcf73..43c8c6665 100644
--- a/test/transpiler/transpiler.test.js
+++ b/test/transpiler/transpiler.test.js
@@ -1984,6 +1984,30 @@ console.log(resolve.length)
       // expectParseError("\u200Ca", 'Unexpected "\\u200c"');
       // expectParseError("\u200Da", 'Unexpected "\\u200d"');
     });
+
+    describe("dead code elimination", () => {
+      const transpilerNoDCE = new Bun.Transpiler({ deadCodeElimination: false });
+      it("should DCE with deadCodeElimination: true or by default", () => {
+        expect(parsed("123", true, false)).toBe("");
+        expect(parsed("[-1, 2n, null]", true, false)).toBe("");
+        expect(parsed("true", true, false)).toBe("");
+        expect(parsed("!0", true, false)).toBe("");
+        expect(parsed('if (!1) "dead";', true, false)).toBe("if (false)");
+        expect(parsed("if (!1) var x = 2;", true, false)).toBe("if (false)\n  var x");
+        expect(parsed("if (undefined) { let y = Math.random(); }", true, false)).toBe("if (undefined) {\n}");
+      });
+      it("should not DCE with deadCodeElimination: false", () => {
+        expect(parsed("123", true, false, transpilerNoDCE)).toBe("123");
+        expect(parsed("[1, 2n, null]", true, false, transpilerNoDCE)).toBe("[1, 2n, null]");
+        expect(parsed("true", true, false, transpilerNoDCE)).toBe("true");
+        expect(parsed("!0", true, false, transpilerNoDCE)).toBe("!0");
+        expect(parsed('if (!1) "dead";', true, false, transpilerNoDCE)).toBe('if (!1)\n  "dead"');
+        expect(parsed("if (!1) var x = 2;", true, false, transpilerNoDCE)).toBe("if (!1)\n  var x = 2");
+        expect(parsed("if (undefined) { let y = Math.random(); }", true, false, transpilerNoDCE)).toBe(
+          "if (undefined) {\n  let y = Math.random();\n}",
+        );
+      });
+    });
   });
 
   it("private identifiers", () => {