Selecting the right W tests

Commands

./wbuild wtest                               # build bin/wtest once
./bin/wtest changed path/to/file.w ...       # print the focused targets
git diff --name-only HEAD | ./bin/wtest changed   # targets for the whole diff
./wbuild test_changed                        # same, and runs them
./bin/wtest changed --verbose ...            # explain file -> target mapping

Run the printed targets with ./wbuild <targets> (independent targets
run in parallel and toolchain builds are content-hash-cached; -j N
overrides the parallelism, --no-cache forces reruns).

Interpreting the mapping

Selection is manifest-driven: bin/wtest generates the manifest at runtime,
so a target is selected when (a) one of its steps names the changed path
(fixtures, grammars, scripts, data files) or (b) one of its compile
roots' transitive import closures contains the changed .w file
(computed via bin/wv2 deps, cached in bin/.wtest_deps_cache — the
first run after a build can take several minutes, printing progress to
stderr and resuming from a checkpoint if interrupted, so budget for it
instead of killing it at two minutes; later runs are sub-second). On top
of that, residue rules documented at the top of tools/test_map.w
cover what the import graph cannot see:

• Compiler-tree files map to verify self_host_warning_test — the
  self-host fixpoint is the key regression guard; run it for every
  compiler/grammar/codegen change, and add verify_x64 when codegen or
  word-size behavior changed.
• Every existing .w change adds parser_generator_w_test (it parses
  every tracked .w file).
• Deleted .w files and lib//structures//libs/ paths add
  metadata_check (declared module trees must resolve to files).
• Docs (docs/, *.md, *.txt) and .cursor/ map to nothing.
• Paths nothing knows about fall back to the full tests umbrella.

A new test target in the manifest is picked up automatically — its steps
name the test file. Add a residue rule in tools/test_map.w only for
coupling the import graph cannot see (run-time data files,
non-default-arch modules).

The full gate

Focused targets are for iteration. Before declaring work done, run the
full suite: ./wbuild tests (includes verify, x64
fixpoint, stdlib/structures, REPL, debugger, dynamic linking, MCP/LSP
and hook tests).