fix(wasm): enable C++ exception catching in the Emscripten build

.github/workflows/build.yml

@@ -70,3 +70,6 @@ jobs:
           test -f nec2pp.js
           test -f nec2pp.wasm
           echo "WASM artifacts present: $(ls -la nec2pp.js nec2pp.wasm)"
+
+      - name: WASM runtime smoke test
+        run: node tests/wasm_smoke.js nec2pp.js

src/CMakeLists.txt

@@ -149,9 +149,15 @@ if(NECPP_BUILD_WASM)
         ${CMAKE_CURRENT_SOURCE_DIR}
         ${NECPP_EIGEN_DIR}
         ${CMAKE_BINARY_DIR})
+    # Emscripten disables exception catching by default. nec_context throws to
+    # unwind a finished solve, so without this the catch is elided and every
+    # completed run escapes as an uncaught error. Needed at compile, not just
+    # link: the link flag cannot restore a catch already dropped.
+    target_compile_options(nec2pp_wasm PRIVATE -fexceptions)
     # Flags carried verbatim from the old Makefile wasm target.
     target_link_options(nec2pp_wasm PRIVATE
         -sWASM=1
+        -fexceptions
         "-sEXPORTED_FUNCTIONS=[\"_nec_create_context\",\"_nec_delete_context\",\"_nec_process_input\",\"_nec_get_output\",\"_nec_get_output_length\",\"_nec_free\"]"
         "-sEXPORTED_RUNTIME_METHODS=[\"ccall\",\"cwrap\",\"UTF8ToString\",\"lengthBytesUTF8\"]"
         -sALLOW_MEMORY_GROWTH=1

tests/wasm_smoke.js

@@ -0,0 +1,48 @@
+// Runtime smoke test for the Emscripten build (nec2pp.js + nec2pp.wasm).
+//
+// Usage: node tests/wasm_smoke.js [path/to/nec2pp.js]
+//
+// Feeds nec_process_input a deck that makes the geometry parser throw a
+// nec_exception and checks it comes back as rc -2 with the message in the
+// output buffer. If the build lacks C++ exception catching, the throw
+// escapes into JS instead and this test fails.
+//
+// nec_process_input is still a stub that parses geometry from stdin rather
+// than from its input string, so stdin is set to EOF here.
+'use strict';
+
+const path = require('path');
+
+const jsPath = path.resolve(process.argv[2] || 'nec2pp.js');
+const M = require(jsPath);
+
+function fail(msg) {
+  console.error('FAIL: ' + msg);
+  process.exit(1);
+}
+
+M.stdin = () => null;
+M.onAbort = (what) => fail('module aborted: ' + what);
+M.onRuntimeInitialized = () => {
+  const ctx = M.ccall('nec_create_context', 'number', [], []);
+  if (!ctx)
+    fail('nec_create_context returned null');
+
+  let rc;
+  try {
+    rc = M.ccall('nec_process_input', 'number', ['number', 'string'],
+                 [ctx, 'CE\nEN\n']);
+  } catch (e) {
+    fail('nec_process_input threw into JS (exception catching disabled?): ' + e);
+  }
+
+  const out = M.UTF8ToString(M.ccall('nec_get_output', 'number', ['number'], [ctx]));
+  M.ccall('nec_delete_context', null, ['number'], [ctx]);
+
+  if (rc !== -2)
+    fail('expected rc -2, got ' + rc + ' (output: ' + JSON.stringify(out) + ')');
+  if (!out.startsWith('Error: GEOMETRY DATA CARD ERROR'))
+    fail('unexpected output: ' + JSON.stringify(out));
+
+  console.log('WASM smoke test passed: ' + out);
+};