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Generate compile_commands.json for an Emscripten project

Run the build under Bear, with Bear as the outermost command:

bear -- emmake make

Bear captures every process the build tree starts, however many wrapper scripts sit in between, so it does not matter that emmake itself sets CC/CXX to emcc/em++ before handing off to make: those exec calls happen inside the tree Bear is already watching. Bear has to be the outermost command for that to hold, so bear -- emmake make is the order to use.

emcc, em++, and their .py-suffixed spellings are recognized under the clang family, not a separate emscripten id, since Emscripten’s driver is a Clang wrapper whose command line follows Clang’s flag syntax closely enough for Bear’s Clang rules to parse it correctly. There is no emscripten as value to write in a compilers: override; use clang if a nonstandard emcc path needs a hint. See Supported compilers for the full recognized-name table.

CMake projects: emcmake

For a CMake-based Emscripten project, emcmake only needs to run once, to generate a build tree configured for emcc/em++; the actual build is what Bear needs to watch:

emcmake cmake -B build
bear -- cmake --build build

This is the same two-step shape as the general CMake case in the bear(1) man page’s EXAMPLES: the generation step does not compile your project’s sources, so it does not need to run under Bear. In wrapper mode (the default on macOS and Windows, or forced with intercept.mode: wrapper), a step that discovers the compiler on its own has to run under Bear too, so run the generation step under Bear as well and discard its output, the same way Generate compile_commands.json for a Makefile project handles ./configure:

bear -- emcmake cmake -B build
bear -- cmake --build build

clangd and an emcc entry

clangd reads the recorded compiler as emcc, a binary it does not run and does not know the way it knows a plain clang. When it cannot infer a driver’s built-in include paths and default target from the recorded command alone, point it at the real driver directly with --query-driver, the same mechanism the bear(1) man page documents for MPI compiler wrappers:

clangd --query-driver=/path/to/emcc

See Set up clangd for a project without CMake for getting the database itself into a place clangd finds it.