commit 352f405f6a834da32449838bf04f5ff68a1f86af
author Richard Levasseur <richardlev@gmail.com> Sun Dec 28 23:40:39 2025 -0800
committer GitHub <noreply@github.com> Mon Dec 29 07:40:39 2025 +0000
tree b4107784d5a9aa4df45f70e2eaf6d83d7062a3b0
parent 2de083f68b74c5fb6b2aedbeea911a70fa2093a5

feat: basic build data with stamping (#3484)

This makes build data accessible to binaries. By default, some basic
information
is always available: target name and if stamping was enabled.

When `--stamp` is enabled, the full `workspace_status_command` output is
included in the
build information.

Build information is made available through a special
`bazel_binary_info` module. This
module is created by the bootstrap and injected into sys.modules. It
provides an API
for gettting the raw build information that was written. Exposing a
module, instead
of a file, is done insulate from the Bazel-ism of runfiles.

When stamping is enabled, the way stamped data works is a bit round
about to get
the desired semantics: that the build data reflects the most recent
build of a
binary, not the last cached value of the build information (e.g., if I
build
a binary, then modify a file in the binary, then build again, the build
data
should reflect the timestamp of the second build). Normal Bazel caching,
however,
makes that somewhat difficult (the build data file has to take the full
transitive
set of files as inputs to properly detect changes, otherwise it'll get
cached
on first build of the binary; plus actions can't take runfiles objects
as inputs).

To work around this, we use some special APIs to get `ctx.version_file`
information
into the output without entirely destroying caching.

* Because `ctx.version_file` doesn't trigger cache invalidation, a
special helper,
`py_internal.copy_without_caching()`, is used to make it _always_
invalidate
caching. Now we can ensure we have a copy of the most recent invocation
data.
* To prevent the above from _always_ rebuilding a binary, another
special api,
`py_internal.declare_constant_metadata_file()` is used to restore the
behavior
  of a file never invalidating caching (even if it changes).

This dance is necessary because actions can't take runfiles as direct
inputs. It
also avoids having to pass the entire program's transitive set of files
as an input
just to do input change tracking.

Note the above only applies when stamping is enabled. Unstamped binaries
don't
do any of this.

Along the way...

* The `stamp` attribute now transitions the `--stamp` flag. This was
necessary so that
  the dependency on version_info was conditional on stamping.
* Remove a defunct helper from the stage2 bootstrap code.