cc-wrappers

C/C++ compiler wrapper scripts to generate compile_commands.json.

How to use

• Ensure deno is in PATH
• Set CC_UNWRAPPED/CXX_UNWRAPPED environment variables to point to the real C/C++ compiler
• Configure the project with CC/CXX to point to absolute paths of cc.js/cxx.js
• Any command that may invoke cc.js/cxx.js must be wrapped with server.js, e.g. /foo/server.js ./configure CC=/foo/cc.js CXX=/foo/cxx.js or /foo/server.js hadrian/build -j
• When the build finishes, server.js writes compile_commands.json to its working directory

How it works

• server.js binds to a random port and starts an http server, the server address is passed to all subprocesses via CC_WRAPPERS_SERVER.
• cc.js/cxx.js checks their arguments, if there's -c, they assume they're being used to compile stuff, generate a compile_commands.json entry, post to the server and wait for server ack.
• Regardless of whether cc.js/cxx.js is invoked with -c, they'll invoke the actual unwrapped compiler with the same arguments, exit with the same exit code, and do not mess with stdout/stderr.
• cxx.js symlinks to cc.js, they decide whether to invoke CC_UNWRAPPED/CXX_UNWRAPPED by checking if import.meta.url is cc.js/cxx.js.
• When the build process completes, server.js has recorded all invocations of cc.js/cxx.js. It then does some filtering, checking whether the source file actually still exist, if not that's likely a boring auto-generated source file and gets dropped.
• server.js pretty-prints compile_commands.json and exits with the same exit code of the build process.

Why

Some build systems don't support emitting compile_commands.json yet. There's bear, but bear has its own limits and don't always reliably work, e.g. it doesn't work for hadrian at all, at least when cross compiling GHC.

I came up with this low-tech wrapper idea as a showerthought. I'm pretty sure I'm not the first one to put up an implementation, if there's prior art I'd be glad to hear.

TODOs

• More principled response file parsing logic
• More filtering/dedupe logic to avoid confusing the IDE with multiple entries of the same source file
• Make it incremental, support appending to existing compile_commands.json
• Support different C/C++ compiler combinations in the same run, e.g. due to the need of cross compilation
• Support invoking other compiler wrappers like ccache