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build: compute version/commit/date once, not per sub-make recursion 

MAGIC_VERSION/REVISION/COMMIT/BUILDDATE used `?=` with `$(shell ...)`, which
makes them recursively-expanded.  Because they are exported, make re-evaluated
(re-spawned git/date/cat) every time it built a child's environment -- so a
no-op recursive `make` spawned git and date ~624 times each.

Guard each with `ifndef` and assign with `:=` (simply-expanded) so the value is
computed once at the top and exported as a plain string; sub-makes inherit it
and the ifndef skips recomputation.  This was the last "fold in" item from the
buildinfo/ccache plan.

Verified: a no-op `make` now spawns git and date once each (was 624); a full
clean build spawns 1 git / 2 date / 10 cat; the commit is still embedded
correctly and builds are reproducible.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Darryl L. Miles 2026-07-23 15:42:19 +00:00 committed by R. Timothy Edwards
parent 92d13c9894
commit 0aacd546c9
1 changed files with 18 additions and 5 deletions
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23
scripts/defs.mak.in
View File

@ -119,27 +119,40 @@ LIB_SPECS_GRNULL = @LIB_SPECS_GRNULL@
WISH_EXE = @WISH_EXE@ WISH_EXE = @WISH_EXE@
TCL_LIB_DIR = @TCL_LIB_DIR@ TCL_LIB_DIR = @TCL_LIB_DIR@
MAGIC_VERSION ?= $(shell cat ${MAGICSRC}/VERSION | cut -d. -f1-2) # Computed once, simply-expanded (:=), and exported below. Sub-makes inherit the
MAGIC_REVISION ?= $(shell cat ${MAGICSRC}/VERSION | cut -d. -f3) # resulting strings and the `ifndef` guards skip recomputation -- so git/date/cat
# run once at the top instead of being re-spawned every time make rebuilds the
# recursively-expanded export for a child (a no-op recursive make otherwise spawns
# each of them hundreds of times).
ifndef MAGIC_VERSION
MAGIC_VERSION := $(shell cat ${MAGICSRC}/VERSION | cut -d. -f1-2)
endif
ifndef MAGIC_REVISION
MAGIC_REVISION := $(shell cat ${MAGICSRC}/VERSION | cut -d. -f3)
endif
# git may be absent (source tarball) or ${MAGICSRC} not a work-tree: fall back to # git may be absent (source tarball) or ${MAGICSRC} not a work-tree: fall back to
# empty rather than emitting an error. # empty rather than emitting an error.
MAGIC_COMMIT ?= $(shell git -C ${MAGICSRC} rev-parse HEAD 2>/dev/null) ifndef MAGIC_COMMIT
MAGIC_COMMIT := $(shell git -C ${MAGICSRC} rev-parse HEAD 2>/dev/null)
endif
# "-DMAGIC_NO_BUILDDATE" when configured with --disable-magic-builddate, else # "-DMAGIC_NO_BUILDDATE" when configured with --disable-magic-builddate, else
# empty. buildinfo.c reports an empty MagicCompileTime under that define. # empty. buildinfo.c reports an empty MagicCompileTime under that define.
MAGIC_BUILDDATE_DEFS = @MAGIC_BUILDDATE_DEFS@ MAGIC_BUILDDATE_DEFS = @MAGIC_BUILDDATE_DEFS@
# Only compute the (volatile) build date when it will actually be baked in -- # Only compute the (volatile) build date when it will actually be baked in --
# skipping it under --disable-magic-builddate avoids the parse-time date spawn. # skipping it under --disable-magic-builddate avoids the date spawn entirely.
ifeq (${MAGIC_BUILDDATE_DEFS},) ifeq (${MAGIC_BUILDDATE_DEFS},)
ifndef MAGIC_BUILDDATE
# Honor SOURCE_DATE_EPOCH (reproducible builds -- appimage/npm tarballs) when set, # Honor SOURCE_DATE_EPOCH (reproducible builds -- appimage/npm tarballs) when set,
# else the current time. @SOURCE_DATE_CMD@ is the platform's epoch->UTC-date # else the current time. @SOURCE_DATE_CMD@ is the platform's epoch->UTC-date
# invocation, chosen by configure (GNU `date -u -d @` / `gdate` vs BSD # invocation, chosen by configure (GNU `date -u -d @` / `gdate` vs BSD
# `date -u -r `); the epoch is appended here. The SOURCE_DATE_EPOCH branch is # `date -u -r `); the epoch is appended here. The SOURCE_DATE_EPOCH branch is
# UTC so a reproducible stamp does not depend on the builder's zone; the plain # UTC so a reproducible stamp does not depend on the builder's zone; the plain
# `date` fallback is local. # `date` fallback is local.
MAGIC_BUILDDATE ?= $(shell if [ -n "$$SOURCE_DATE_EPOCH" ]; then \ MAGIC_BUILDDATE := $(shell if [ -n "$$SOURCE_DATE_EPOCH" ]; then \
@SOURCE_DATE_CMD@$$SOURCE_DATE_EPOCH; \ @SOURCE_DATE_CMD@$$SOURCE_DATE_EPOCH; \
else date; fi | tr -d '\r\n') else date; fi | tr -d '\r\n')
endif endif
endif
# This allow inheritence of the values from toplevel Makefile # This allow inheritence of the values from toplevel Makefile
export MAGIC_VERSION export MAGIC_VERSION