Remove EM_LOG_C_STACK feature of emscripten_log (#23553)

This was supported by `emscripten-source-map.min.js` which seems like
minified source map parser, but I don't think this feature has worked
for at least 4 years since we switched to using wasm and wasm source
maps.

This feature was part of `emscripten_log` since it was first added in
26d6ad3 but I know of anyone that ever used it.

Fixes: #13089

Author: sbc100

.gitattributes

@@ -4,7 +4,6 @@ tools/crunch-worker.js -diff
 third_party/lzma.js/lzma-decoder.js -diff
 third_party/lzma.js/lzma-full.js -diff
 test/other/test_emsize.js -diff
-src/emscripten-source-map.min.js -diff
 test/* linguist-vendored
 third_party/* linguist-vendored
 system/ linguist-vendored

ChangeLog.md

@@ -25,6 +25,12 @@ See docs/process.md for more on how version tagging works.
   emcc itself.  This enables support for C++20 in cmake projects. (#21987)
 - The version of python required to run emscripten was bumped from 3.6 to 3.8.
   (#23417)
+- The `EM_LOG_C_STACK` flag to `emscripten_log` was deprecated and the helper
+  file on which it was based (`emscripten-source-map.min.js`) deleted.  This
+  feature (userspace source map parsing in logs) was never ported to wasm
+  source maps, so it has not worked in many years, and there have been no
+  requests for it. This has no impact on the source map support in browser
+  devtools. (#23553)
 
 4.0.2 - 01/30/25
 ----------------

eslint.config.mjs

@@ -47,7 +47,6 @@ export default [{
     'src/gl-matrix.js',
     'src/headless.js',
     'src/headlessCanvas.js',
-    'src/emscripten-source-map.min.js',
     'src/source_map_support.js',
     'src/Fetch.js',
     'src/settings.js',

src/emscripten-source-map.min.js

@@ -20,13 +20,11 @@ var LibraryStackTrace = {
     var iNextLine = callstack.indexOf('\n', Math.max(iThisFunc, iThisFunc2))+1;
     callstack = callstack.slice(iNextLine);
 
-    // If user requested to see the original source stack, but no source map
-    // information is available, just fall back to showing the JS stack.
-    if (flags & {{{ cDefs.EM_LOG_C_STACK }}} && typeof emscripten_source_map == 'undefined') {
-      warnOnce('Source map information is not available, emscripten_log with EM_LOG_C_STACK will be ignored. Build with "--pre-js $EMSCRIPTEN/src/emscripten-source-map.min.js" linker flag to add source map loading to code.');
-      flags ^= {{{ cDefs.EM_LOG_C_STACK }}};
-      flags |= {{{ cDefs.EM_LOG_JS_STACK }}};
+#if ASSERTIONS
+    if (flags & {{{ cDefs.EM_LOG_C_STACK }}}) {
+      warnOnce('emscripten_log with EM_LOG_C_STACK no longer has any effect');
     }
+#endif
 
     // Process all lines:
     var lines = callstack.split('\n');
@@ -72,23 +70,11 @@ var LibraryStackTrace = {
         }
       }
 
-      var haveSourceMap = false;
-
-      if (flags & {{{ cDefs.EM_LOG_C_STACK }}}) {
-        var orig = emscripten_source_map.originalPositionFor({line: lineno, column: column});
-        haveSourceMap = orig?.source;
-        if (haveSourceMap) {
-          if (flags & {{{ cDefs.EM_LOG_NO_PATHS }}}) {
-            orig.source = orig.source.substring(orig.source.replace(/\\/g, "/").lastIndexOf('/')+1);
-          }
-          callstack += `    at ${symbolName} (${orig.source}:${orig.line}:${orig.column})\n`;
-        }
-      }
-      if ((flags & {{{ cDefs.EM_LOG_JS_STACK }}}) || !haveSourceMap) {
+      if ((flags & {{{ cDefs.EM_LOG_C_STACK | cDefs.EM_LOG_JS_STACK }}})) {
         if (flags & {{{ cDefs.EM_LOG_NO_PATHS }}}) {
           file = file.substring(file.replace(/\\/g, "/").lastIndexOf('/')+1);
         }
-        callstack += (haveSourceMap ? (`     = ${symbolName}`) : (`    at ${symbolName}`)) + ` (${file}:${lineno}:${column})\n`;
+        callstack += `    at ${symbolName} (${file}:${lineno}:${column})\n`;
       }
     }
     // Trim extra whitespace at the end of the output.

src/lib/libstack_trace.js

@@ -53,9 +53,6 @@ void __attribute__((noinline)) bar(int = 0, char * = 0, double = 0) {
     MYASSERT(1 == 1, "");
 
   int flags = EM_LOG_NO_PATHS | EM_LOG_JS_STACK | EM_LOG_FUNC_PARAMS;
-#ifndef RUN_FROM_JS_SHELL
-  flags |= EM_LOG_C_STACK;
-#endif
 
   // We can programmatically get the callstack.
   // 1. Ask for callstack length:
@@ -79,16 +76,7 @@ void __attribute__((noinline)) bar(int = 0, char * = 0, double = 0) {
 
     but the line numbers will greatly vary depending on the mode we are compiling in, so cannot test with direct string comparison. */
 
-  if ((flags & EM_LOG_C_STACK) != 0) {
-    // TODO(https://github.com/emscripten-core/emscripten/issues/13089)
-    // We should be able to check for emscripten_log.cpp here but sadly
-    // source maps seems to be broken under wasm.
-#if 0
-    MYASSERT(!!strstr(callstack, ".cpp:"), "Callstack was %s!", callstack);
-#endif
-  } else {
-    MYASSERT(!!strstr(callstack, ".js:"), "Callstack was %s!", callstack);
-  }
+  MYASSERT(!!strstr(callstack, ".js:"), "Callstack was %s!", callstack);
   MYASSERT(!!strstr(callstack, "bar(int, char*, double)"), "Callstack was %s!", callstack);
   MYASSERT(!!strstr(callstack, "void Foo<int>()"), "Callstack was %s!", callstack);
 

test/emscripten_log/emscripten_log.cpp

@@ -356,8 +356,7 @@ def test_zzz_html_source_map(self):
 ''')
 
   def test_emscripten_log(self):
-    self.btest_exit('emscripten_log/emscripten_log.cpp',
-                    args=['-Wno-deprecated-pragma', '--pre-js', path_from_root('src/emscripten-source-map.min.js'), '-gsource-map'])
+    self.btest_exit('emscripten_log/emscripten_log.cpp', args=['-Wno-deprecated-pragma', '-gsource-map'])
 
   @also_with_wasmfs
   def test_preload_file(self):

test/test_browser.py

@@ -7864,9 +7864,7 @@ def test_modularize_closure_pre(self):
   @no_wasm2js('symbol names look different wasm2js backtraces')
   @also_with_wasm_bigint
   def test_emscripten_log(self):
-    if '-g' not in self.emcc_args:
-      self.emcc_args.append('-g')
-    self.emcc_args += ['-DRUN_FROM_JS_SHELL', '-Wno-deprecated-pragma']
+    self.emcc_args += ['-g', '-DRUN_FROM_JS_SHELL', '-Wno-deprecated-pragma']
     self.do_run_in_out_file_test('emscripten_log/emscripten_log.cpp', interleaved_output=False)
     # test closure compiler as well
     if self.maybe_closure():