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build: reduce the srcdir derivation to a minimal fallback 

Every converted module sets srcdir=@srcdir@ and VPATH=@srcdir@
before including defs.mak, so the full srcdir derivation is now reached
only by readline/ (never converted) and the top-level Makefile.  Neither
compiles magic sources through the pattern rules, so neither needs VPATH.

Drop the MODULE_SUBPATH variable and the VPATH derivation; keep just a
one-line srcdir fallback so CPPFLAGS (-I${srcdir}) stays well-formed for
those two.  BUILD_TOP is retained (GENINC still needs it).

Verified rc=0: out-of-tree Tcl (375) + in-tree Tcl (375, header present) +
out-of-tree --without-tcl (readline/libreadline.a + magic/magic built
through the fallback).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Darryl L. Miles 2026-07-22 19:07:50 +00:00 committed by R. Timothy Edwards
parent 79e6863aa8
commit 69dff2aaa8
1 changed files with 10 additions and 20 deletions
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30
scripts/defs.mak.in
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@ -15,28 +15,18 @@ SHELL = @SHELL@
# to the *source* top. For an in-tree build the two trees coincide.
MAGICSRC = @abs_top_srcdir@
# Derive this module's source directory (and VPATH) from where make is running
# (CURDIR, a build directory) relative to the build top (abspath of MAGICDIR):
# build top = $(abspath $(MAGICDIR))
# subpath = "/tiles", or "" at the top
# srcdir = $(MAGICSRC)$(subpath)
# BUILD_TOP is the absolute build top; GENINC (below) needs it either way.
BUILD_TOP := $(abspath $(MAGICDIR))
# Dual mode: a module converted to Makefile.in sets `srcdir` (and VPATH) from
# @srcdir@ *before* including this file, so we only derive them when it did not.
# This lets the two kinds of Makefile coexist during the migration. BUILD_TOP
# (needed by GENINC below) is computed either way.
# Minimal srcdir fallback. Every module converted to Makefile.in sets
# `srcdir` (and VPATH) from @srcdir@ *before* including this file. The only
# Makefiles that do NOT are readline/ (intentionally never converted) and the
# top-level Makefile; neither compiles magic sources through the pattern rules, so
# neither needs VPATH. We only default `srcdir` -- derived from where make is
# running (CURDIR, a build dir) relative to BUILD_TOP -- so that CPPFLAGS, which
# lists -I${srcdir}, stays well-formed. The patsubst is an anchored prefix strip:
# "" at the build top, "/readline" in the readline subdir.
ifeq ($(origin srcdir),undefined)
# Anchored prefix strip (patsubst matches the whole word, so BUILD_TOP must be a
# leading prefix): "" at the build top, "/tiles" in a subdir. Unlike $(subst …)
# this cannot mis-fire if BUILD_TOP happens to recur later in the path.
MODULE_SUBPATH := $(patsubst $(BUILD_TOP)%,%,$(CURDIR))
srcdir := $(MAGICSRC)$(MODULE_SUBPATH)
# Only set VPATH inside a module (sub)directory, never at the build top: a
# top-level VPATH into the source tree could let a stale source-tree
# database/database.h shadow the copy we must (re)generate in the build tree.
ifneq ($(MODULE_SUBPATH),)
VPATH := $(srcdir)
endif
srcdir := $(MAGICSRC)$(patsubst $(BUILD_TOP)%,%,$(CURDIR))
endif
# Generated headers (currently just database/database.h) are exposed through a