Rust/Emscripten generates invalid JS from Rust-mangled symbols #24825
Description
See https://github.com/nickpdemarco/emsdk-export-bug for a minimum reproducible example (simply clone and run make test). The output of this example is appended to the bottom of this report.
Version of emscripten/emsdk:
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 4.0.12-git (40782fe7671409b64da6d73bc84aad3b2c5e4a07)
clang version 22.0.0git (https:/github.com/llvm/llvm-project 61500345787e6fc66e6b6b8a249feaf98c839fbe)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /Users/demarco/repos/emsdk/upstream/bin
Build config: +assertions
Failing command line in full:
This is a run-time failure, but it is caused by the emission of invalid JavaScript.
Full link command and output with -v appended:
➜ emsdk-export-bug git:(main) ✗ make test
RUSTFLAGS="-C link-arg=--no-entry -C link-arg=-sSIDE_MODULE=1" cargo build --target wasm32-unknown-emscripten
Compiling rust_lib v0.1.0 (/Users/demarco/repos/emsdk-export-bug)
Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.09s
em++ -v -s MAIN_MODULE=1 -o main.js main.cpp target/wasm32-unknown-emscripten/debug/rust_lib.wasm
"/Users/demarco/repos/emsdk/upstream/bin/clang++" -target wasm32-unknown-emscripten -fignore-exceptions -fPIC -fvisibility=default -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr --sysroot=/Users/demarco/repos/emsdk/upstream/emscripten/cache/sysroot -DEMSCRIPTEN -Xclang -iwithsysroot/include/fakesdl -Xclang -iwithsysroot/include/compat -v -c main.cpp -o /var/folders/zm/ll4504dd6dgbvy20y9ls2_hr0000gq/T/emscripten_temp_w2qdgjzf/main_0.o
clang version 22.0.0git (https:/github.com/llvm/llvm-project 61500345787e6fc66e6b6b8a249feaf98c839fbe)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /Users/demarco/repos/emsdk/upstream/bin
Build config: +assertions
(in-process)
"/Users/demarco/repos/emsdk/upstream/bin/clang-22" -cc1 -triple wasm32-unknown-emscripten -emit-obj -disable-free -clear-ast-before-backend -main-file-name main.cpp -mrelocation-model pic -pic-level 2 -mframe-pointer=none -ffp-contract=on -fno-rounding-math -mconstructor-aliases -target-feature +mutable-globals -target-cpu generic -debugger-tuning=gdb -fdebug-compilation-dir=/Users/demarco/repos/emsdk-export-bug -v -fcoverage-compilation-dir=/Users/demarco/repos/emsdk-export-bug -resource-dir /Users/demarco/repos/emsdk/upstream/lib/clang/22 -D EMSCRIPTEN -isysroot /Users/demarco/repos/emsdk/upstream/emscripten/cache/sysroot -internal-isystem /Users/demarco/repos/emsdk/upstream/emscripten/cache/sysroot/include/wasm32-emscripten/c++/v1 -internal-isystem /Users/demarco/repos/emsdk/upstream/emscripten/cache/sysroot/include/c++/v1 -internal-isystem /Users/demarco/repos/emsdk/upstream/lib/clang/22/include -internal-isystem /Users/demarco/repos/emsdk/upstream/emscripten/cache/sysroot/include/wasm32-emscripten -internal-isystem /Users/demarco/repos/emsdk/upstream/emscripten/cache/sysroot/include -fdeprecated-macro -ferror-limit 19 -fmessage-length=133 -fvisibility=default -fgnuc-version=4.2.1 -fskip-odr-check-in-gmf -fcxx-exceptions -fignore-exceptions -fexceptions -fcolor-diagnostics -iwithsysroot/include/fakesdl -iwithsysroot/include/compat -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr -o /var/folders/zm/ll4504dd6dgbvy20y9ls2_hr0000gq/T/emscripten_temp_w2qdgjzf/main_0.o -x c++ main.cpp
clang -cc1 version 22.0.0git based upon LLVM 22.0.0git default target x86_64-apple-darwin24.5.0
ignoring nonexistent directory "/Users/demarco/repos/emsdk/upstream/emscripten/cache/sysroot/include/wasm32-emscripten/c++/v1"
ignoring nonexistent directory "/Users/demarco/repos/emsdk/upstream/emscripten/cache/sysroot/include/wasm32-emscripten"
#include "..." search starts here:
#include <...> search starts here:
/Users/demarco/repos/emsdk/upstream/emscripten/cache/sysroot/include/fakesdl
/Users/demarco/repos/emsdk/upstream/emscripten/cache/sysroot/include/compat
/Users/demarco/repos/emsdk/upstream/emscripten/cache/sysroot/include/c++/v1
/Users/demarco/repos/emsdk/upstream/lib/clang/22/include
/Users/demarco/repos/emsdk/upstream/emscripten/cache/sysroot/include
End of search list.
/Users/demarco/repos/emsdk/upstream/bin/clang --version
/Users/demarco/repos/emsdk/upstream/bin/wasm-ld @/var/folders/zm/ll4504dd6dgbvy20y9ls2_hr0000gq/T/emscripten_fgot3vus.rsp.utf-8
/Users/demarco/repos/emsdk/upstream/bin/wasm-ld @/var/folders/zm/ll4504dd6dgbvy20y9ls2_hr0000gq/T/emscripten_b3j8wp3w.rsp.utf-8
/Users/demarco/repos/emsdk/upstream/bin/llvm-objcopy main.wasm main.wasm '--remove-section=.debug*' --remove-section=producers --remove-section=name
/Users/demarco/repos/emsdk/node/22.16.0_64bit/bin/node /Users/demarco/repos/emsdk/upstream/emscripten/tools/compiler.mjs -
node main.js
/Users/demarco/repos/emsdk-export-bug/main.js:4572
function __ZN102_$LT$std..panicking..begin_panic_handler..FormatStringPayload$u20$as$u20$core..panic..PanicPayload$GT$3get17hecee4b43e7ecbd58E(...args
^
SyntaxError: Unexpected token '.'
at wrapSafe (node:internal/modules/cjs/loader:1281:20)
at Module._compile (node:internal/modules/cjs/loader:1321:27)
at Module._extensions..js (node:internal/modules/cjs/loader:1416:10)
at Module.load (node:internal/modules/cjs/loader:1208:32)
at Module._load (node:internal/modules/cjs/loader:1024:12)
at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:174:12)
at node:internal/main/run_main_module:28:49
Node.js v20.15.1
make: *** [test] Error 1