feat: add BinaryenExpressionAllocateAndWriteText by chharvey · Pull Request #8717 · WebAssembly/binaryen

chharvey · 2026-05-16T23:39:32Z

adds a function for returning a string representation of an expression in s-expression format.

stevenfontanella · 2026-05-19T17:45:57Z

+  auto str = os.str();
+  const size_t len = str.length() + 1;
+  char* output = (char*)malloc(len);
+  std::copy_n(str.c_str(), len, output);


copy_n is a little strange for copying bytes, can we use strncpy or memcpy instead to convey the intent better?

I'm honestly not sure, i just copied the exact code from BinaryenModuleAllocateAndWriteText.

I'll defer to the C developers for what's best. I'm happy as long as it's consistent.

I agree with @stevenfontanella , but yeah, let's keep it consistent here. We can simplify all these copy_n uses separately.

stevenfontanella · 2026-05-19T17:47:01Z

+// Serialize an expression in s-expression form. Implicitly allocates the returned
+// char* with malloc(), and expects the user to free() them manually
+// once not needed anymore.
+BINARYEN_API char* BinaryenExpressionAllocateAndWriteText(BinaryenExpressionRef expr);


Let's add a CHANGELOG.md entry for this and unit tests in test/example/c-api-kitchen-sink.c / test/example/c-api-kitchen-sink.txt.

kripken

lgtm with @stevenfontanella 's comment about the changelog and testing

kripken · 2026-05-19T20:17:15Z

+  auto str = os.str();
+  const size_t len = str.length() + 1;
+  char* output = (char*)malloc(len);
+  std::copy_n(str.c_str(), len, output);


I agree with @stevenfontanella , but yeah, let's keep it consistent here. We can simplify all these copy_n uses separately.

stevenfontanella · 2026-05-19T23:54:31Z

+  const textPtr = BinaryenObj["_BinaryenExpressionAllocateAndWriteText"](expr);
+  const text = UTF8ToString(textPtr);
+  if (textPtr) _free(textPtr);


Can we use try ... finally here to ensure that the pointer is freed even if UTF8ToString throws an exception? I can't find the definition of UTF8ToString so I'm not sure if that's possible, but it conveys the intent better especially in case this code changes.

Also, we typically use braces around if bodies, let's do that here.

sure, i again copied from the emitText for Modules but i can make the same updates to both.

also… digging into this project helped me learn a lot about Emscripten and where all this stuff like UTF8ToString comes from. see my .d.ts file here for a quasi-explanation. Looks like Emscripten declares it here

kripken

Looks good, but please add a test for the new API.

chharvey · 2026-05-23T04:27:37Z

@kripken Can you point me to directions on how to do that? I ran cmake . && make and then ./check.py but got the error:

AssertionError:
File "./check.py", line 54, in run_version_tests
assert executables
       ^^^^^^^^^^^

Also i wouldn't know how/where to add tests… is there a high-level list of steps? -Thanks

kripken · 2026-05-26T20:31:29Z

@chharvey for a JS test, see build-emscripten in .github/workflows/ci.yml. That does some setup and then calls ./scripts/emcc-tests.sh, so you can follow those steps locally.

For where the tests are, see e.g. #8660 which added related tests.

kripken · 2026-05-28T21:19:23Z

Looks like there are errors on CI. At least one might be fixed by merging in latest main.

chharvey · 2026-05-28T22:55:40Z

@kripken I just pulled in the latest from main (a6f59c6) but still seeing this error when running tests locally:

Traceback (most recent call last):
  File "/bin/binaryen-lit", line 18, in <module>
    from lit.main import main
ModuleNotFoundError: No module named 'lit'
Traceback (most recent call last):
  File "/./check.py", line 492, in <module>
    sys.exit(main())
             ~~~~^^
  File "/./check.py", line 474, in main
    TEST_SUITES[test]()
    ~~~~~~~~~~~~~~~~~^^
  File "/./check.py", line 427, in wrapper
    raise Exception(f'test suite failed: {name}')
Exception: test suite failed: lit

kripken · 2026-06-02T16:59:51Z

Which specific lit test is failing? You can run ./check.py lit to run just the lit tests, then can run lit -v [TEST] to run a specific test to debug it.

stevenfontanella · 2026-06-02T17:11:52Z

@chharvey Looks like you need to pip install lit

chharvey · 2026-06-03T04:30:36Z

I installed lit but seeing these failures:

Failed Tests (15):
  Binaryen lit tests :: fuzz-types.test
  Binaryen lit tests :: help/wasm-as.test
  Binaryen lit tests :: help/wasm-ctor-eval.test
  Binaryen lit tests :: help/wasm-dis.test
  Binaryen lit tests :: help/wasm-emscripten-finalize.test
  Binaryen lit tests :: help/wasm-fuzz-types.test
  Binaryen lit tests :: help/wasm-merge.test
  Binaryen lit tests :: help/wasm-metadce.test
  Binaryen lit tests :: help/wasm-opt.test
  Binaryen lit tests :: help/wasm-reduce.test
  Binaryen lit tests :: help/wasm-shell.test
  Binaryen lit tests :: help/wasm-split.test
  Binaryen lit tests :: help/wasm2js.test
  Binaryen lit tests :: merge/manifest.wat
  Binaryen lit tests :: passes/stack-ir-eh-legacy.wast

I'm running:

Python 3.14.5 (/opt/homebrew/bin/python3 -> ../Cellar/python@3.14/3.14.5/bin/python3)
pip 26.1.1 from /opt/homebrew/lib/python3.14/site-packages/pip (python 3.14)
lit (/opt/homebrew/bin/lit) version 0.11.0.post1
filecheck (/opt/homebrew/opt/llvm@18/bin/filecheck) Homebrew LLVM version 18.1.8
macOS Tahoe 26.5.1

I even tried running tests from main branch (latest at 5e0ad2c) and still getting the same errors.

Also, not sure why the CI is failing… looks unrelated to this PR.

chharvey · 2026-06-03T06:39:01Z

update: found the problem. i forgot the trailing newline from the original function. all mjs tests are passing now

feat: add BinaryenExpressionAllocateAndWriteText

6457bc6

chharvey requested a review from a team as a code owner May 16, 2026 23:39

chharvey requested review from stevenfontanella and removed request for a team May 16, 2026 23:39

chharvey mentioned this pull request May 16, 2026

Please provide a stringify-expression function in the C libarary #8716

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stevenfontanella reviewed May 19, 2026

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kripken reviewed May 19, 2026

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chharvey added 2 commits May 19, 2026 19:29

fix: lint

b3f7afb

feat: update Module['emitText'] to use new C api

fdbba7f

stevenfontanella reviewed May 19, 2026

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chharvey added 2 commits May 19, 2026 20:14

fix: wrap UTF8ToString in try–finally

8f69c85

fixup! fdbba7f

0843a21

kripken reviewed May 21, 2026

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chharvey added 2 commits May 27, 2026 10:48

Merge branch 'main' into feat/8716-stringify-expression

b6f3d67

test: add test to kitchen sink

4ad5310

Merge branch 'main' into feat/8716-stringify-expression

29c5bb4

Merge branch 'main' into feat/8716-stringify-expression

54515a3

fix: forgot trailing newline

b60beb4

kripken approved these changes Jun 5, 2026

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kripken merged commit 32a8e1b into WebAssembly:main Jun 5, 2026
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chharvey deleted the feat/8716-stringify-expression branch June 6, 2026 00:29

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