Just: cut format.just's comments back to what the code cannot say

The file had grown 45 lines of comment around 29 of code, most of it restating
what is visible or belonging in the README. What is left is the part a reader
cannot recover: why the buildifier target is bypassed, why the two exclusion
lists must stay in step, and what silently breaks if `[no-cd]` is dropped.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: redsun82

misc/just/format.just

@@ -6,61 +6,31 @@ _py_formatter := if SEMMLE_CODE != "" { "uv run black" } else { "black" }
 
 _cpp_formatter := if SEMMLE_CODE != "" { "uv run clang-format" } else { "clang-format" }
 
-# The `buildifier` bazel target always covers the whole workspace, so the binary it wraps
-# is used instead and given paths. Naming that binary by its external label rather than
-# through a local alias keeps it valid from any workspace. bazel is asked from the root of
-# this repository, even when it sits inside another, and the files are bounded to that root
-# as well: each repository then formats its own bazel files with the buildifier version it
-# pins, and a verb aimed at a tree spanning both is answered once by each. This is the
-# opposite of building, where a target needs the enclosing workspace to resolve at all,
-# hence `_bazel` in build.just going the other way.
+# The `buildifier` target formats a whole workspace and so cannot take a path, so its
+# binary is driven directly. bazel is asked from this repository's root even when it sits
+# inside another, and the files are bounded to it, so each repository formats its own with
+# the version it pins. Building needs the enclosing workspace instead, hence `_bazel`.
 _bazel_workspace := quote(parent_directory(parent_directory(source_dir())))
 
-# As with the formatters above, an internal repository checkout has its own launcher and
-# that is the one to use. Unlike `_bazel` in build.just it is not `cd`ed to: the workspace
-# is picked by `--chdir` below, so the launcher only has to be found, not entered.
 _bazel_formatter := (if SEMMLE_CODE != "" { '"$SEMMLE_CODE/tools/bazel"' } else { "bazel" }) + " run --noshow_progress --ui_event_filters=,+error,+fail @buildifier_prebuilt//:buildifier --"
 
-# bazel files are named rather than suffixed, and buildifier has no exclude option of its
-# own, so the files skipped by the target above are skipped here too. That target formats
-# the whole workspace at once and so cannot take the path this recipe is given, which is
-# why the two run the same binary through different entry points. Their exclusions are
-# therefore stated twice, in two places, in two syntaxes: keep them in step, or `just
-# format` rewrites what pre-commit and CI deliberately leave alone.
-#
-# bazel knows `BUILD` and `WORKSPACE` by those names and everything else by the `.bazel`
-# extension, so a file named `BUILD.<anything>` else is a template or a generator's input
-# rather than a bazel file, and is none of the formatter's business to parse.
-#
-# Both lists are comma-separated, so a root defining its own `_root_format` can name
-# several patterns in one variable. It has no need to repeat the ones here: the files
-# they cover belong to this repository, which formats them itself. Exclusions match the
-# path as walked rather than as spelled on the command line, so one naming a directory
-# has to cover both the path it is reached by and the path it is walked from.
-#
-# As with the QL formatter, buildifier only names what it rewrote if it also accounts for
-# every file it did not, so that accounting is dropped. It counts the warnings it could
-# not fix there, which are left for linting to report rather than raised on every format.
+# Keep in step with the `buildifier` target's own exclusions, or `just format` rewrites
+# what pre-commit and CI deliberately leave alone. Patterns match the path as walked, so
+# one naming a directory has to cover both how it is reached and how it is walked.
 _bazel_names := "BUILD,WORKSPACE,*.bazel,*.bzl,*.sky"
 
 _bazel_excluded := ".git/*,*/.git/*,*misc/bazel/3rdparty/*_deps/*"
 
+# buildifier only names what it rewrote if it also accounts for every file it did not.
 _bazel_accounting := ': applied fixes, [0-9]+ warnings left$'
 
-# `codeql query format` and `clang-format` take files rather than directories, so the
-# files are collected by `run_on_files.py`. Arguments are passed positionally so that
-# paths containing spaces survive, of which this repository has many.
-#
-# The files that were rewritten are worth reporting, but `codeql query format` only
-# names those once it also names every file it leaves alone, which buries them under
-# thousands of lines. So it is asked for all of it and the lines about files it did not
-# touch are dropped. Only those are dropped, so errors still come through, as does
-# anything unforeseen.
+# These formatters take files rather than directories, so `run_on_files.py` collects them
+# and passes them positionally, which is what lets paths contain spaces. `codeql query
+# format` likewise only reports what it rewrote if it also names everything it did not, so
+# those lines are dropped and nothing else is.
 #
-# `[no-cd]` is what keeps a relative argument meaning the directory the caller is in.
-# The forwarder reaches a recipe above its argument with `--justfile`, which otherwise
-# runs it from that justfile's own directory: dropping the attribute would silently turn
-# the default `.` into the whole repository, and the only symptom would be slowness.
+# `[no-cd]` keeps a relative argument meaning the caller's directory: the forwarder passes
+# `--justfile`, so without it the default `.` would silently become the whole repository.
 
 [no-cd]
 [no-exit-message]