Branch
Hash :
0cc6436e
Author :
Date :
2025-05-29T22:55:00
build: Repair and reduce the CMake build dependency graph
A funny thing happened while refactoring the function argument parsing
in the `PNGGenConfig` module: the processing of dependencies inside
the CMake function `generate_copy` got fixed, thanks to an inadvertent
typo correction!
Going down the rabbit hole, we uncovered two issues:
1. A typo in `scripts/cmake/PNGGenConfig.cmake` caused a dependency
declaration to disappear, disrupting the graph. Fortunately, this
disruption was being mitigated by an additional set of (redundant)
symbolic target declarations that kept the CMake build going.
2. The exact string matching inside `scripts/cmake/gensrc.cmake.in`
imposed an artificial limitation, disallowing the use of absolute
file paths.
The typo correction in (1), and the use of regex matching instead of
exact string matching in (2), allowed us to use absolute file paths
in the main CMake file, consistently, thus allowing CMake to recognize
them as uniquely-identifiable nodes in the dependency graph. There
should be no further need to have extra symbolic targets for proper
node identification.
In the end, we shaved off the redundant symbolic target declarations,
retaining only `png_genfiles` and `png_genprebuilt`.
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# gensrc.cmake.in
# Generate source files with awk, based upon the automake logic.
# Copyright (c) 2022-2024 Cosmin Truta
# Copyright (c) 2016 Glenn Randers-Pehrson
# Written by Roger Leigh, 2016
#
# Use, modification and distribution are subject to
# the same licensing terms and conditions as libpng.
# Please see the copyright notice in png.h or visit
# http://libpng.org/pub/png/src/libpng-LICENSE.txt
#
# SPDX-License-Identifier: libpng-2.0
# Variables substituted from CMakeLists.txt
set(SRCDIR "@CMAKE_CURRENT_SOURCE_DIR@")
set(BINDIR "@CMAKE_CURRENT_BINARY_DIR@")
set(AWK "@AWK@")
set(DFA_XTRA "@DFA_XTRA@")
set(PNG_PREFIX "@PNG_PREFIX@")
set(PNGLIB_VERSION "@PNGLIB_VERSION@")
if(OUTPUT MATCHES "(scripts/pnglibconf\\.c)\$")
# Generate "${BINDIR}/scripts/pnglibconf.c"
file(REMOVE "${BINDIR}/pnglibconf.tf6" "${BINDIR}/pnglibconf.tf7")
execute_process(COMMAND "${CMAKE_COMMAND}" -E echo "com ${PNGLIB_VERSION} STANDARD API DEFINITION"
COMMAND "${AWK}" -f "${SRCDIR}/scripts/options.awk"
"out=pnglibconf.tf6" "logunsupported=1" "version=search"
"${SRCDIR}/pngconf.h" "-"
"${SRCDIR}/scripts/pnglibconf.dfa"
WORKING_DIRECTORY "${BINDIR}"
RESULT_VARIABLE AWK_FAIL)
if(AWK_FAIL)
message(FATAL_ERROR "Failed to generate pnglibconf.tf6")
endif()
execute_process(COMMAND "${AWK}" -f "${SRCDIR}/scripts/options.awk"
"out=pnglibconf.tf7" "pnglibconf.tf6"
WORKING_DIRECTORY "${BINDIR}"
RESULT_VARIABLE AWK_FAIL)
if(AWK_FAIL)
message(FATAL_ERROR "Failed to generate pnglibconf.tf7")
endif()
file(REMOVE "pnglibconf.tf6")
file(MAKE_DIRECTORY "${BINDIR}/scripts")
file(RENAME "pnglibconf.tf7" "${BINDIR}/scripts/pnglibconf.c")
elseif(OUTPUT MATCHES "(pnglibconf\\.c)\$")
# Generate "${BINDIR}/pnglibconf.c"
file(REMOVE "${BINDIR}/pnglibconf.tf4" "${BINDIR}/pnglibconf.tf5")
execute_process(COMMAND "${AWK}" -f "${SRCDIR}/scripts/options.awk"
out=pnglibconf.tf4 version=search
${SRCDIR}/pngconf.h ${SRCDIR}/scripts/pnglibconf.dfa
${SRCDIR}/pngusr.dfa ${DFA_XTRA}
WORKING_DIRECTORY "${BINDIR}"
RESULT_VARIABLE AWK_FAIL)
if(AWK_FAIL)
message(FATAL_ERROR "Failed to generate pnglibconf.tf4")
endif()
execute_process(COMMAND "${AWK}" -f "${SRCDIR}/scripts/options.awk"
out=pnglibconf.tf5 pnglibconf.tf4
WORKING_DIRECTORY "${BINDIR}"
RESULT_VARIABLE AWK_FAIL)
if(AWK_FAIL)
message(FATAL_ERROR "Failed to generate pnglibconf.tf5")
endif()
file(REMOVE "pnglibconf.tf4")
file(MAKE_DIRECTORY "${BINDIR}/scripts")
file(RENAME "pnglibconf.tf5" "${BINDIR}/pnglibconf.c")
elseif(OUTPUT MATCHES "(pnglibconf\\.h)\$")
# Generate "${BINDIR}/pnglibconf.h"
file(REMOVE "${OUTPUT}")
if(PNG_PREFIX)
file(REMOVE "pnglibconf.tf8")
execute_process(COMMAND "${AWK}" "s==0 && NR>1{print prev}
s==0{prev=\$0}
s==1{print \"#define\", \$1, \"${PNG_PREFIX}\" \$1}
s==2{print \"#define ${PNG_PREFIX}png_\" \$1, \"PNG_\" \$1}
END{print prev}" s=0 pnglibconf.out s=1 "${BINDIR}/scripts/prefix.out"
s=2 "${SRCDIR}/scripts/macro.lst"
OUTPUT_FILE pnglibconf.tf8
RESULT_VARIABLE AWK_FAIL)
if(AWK_FAIL)
message(FATAL_ERROR "Failed to generate pnglibconf.tf8")
endif()
file(RENAME "pnglibconf.tf8" "${OUTPUT}")
else()
execute_process(COMMAND "${CMAKE_COMMAND}" -E copy "pnglibconf.out"
"${OUTPUT}"
WORKING_DIRECTORY "${BINDIR}"
RESULT_VARIABLE COPY_FAIL)
if(COPY_FAIL)
message(FATAL_ERROR "Failed to create pnglibconf.h")
endif()
endif()
elseif(OUTPUT MATCHES "(pngprefix\\.h)\$")
# Generate "${BINDIR}/pngprefix.h"
file(REMOVE "${OUTPUT}")
if(PNG_PREFIX)
file(REMOVE "pngprefix.tf1")
execute_process(COMMAND "${AWK}"
"{print \"#define\", \$1, \"${PNG_PREFIX}\" \$1}"
"${BINDIR}/scripts/intprefix.out"
OUTPUT_FILE "pngprefix.tf1"
RESULT_VARIABLE AWK_FAIL)
if(AWK_FAIL)
message(FATAL_ERROR "Failed to generate pngprefix.tf1")
endif()
file(RENAME "pngprefix.tf1" "${OUTPUT}")
else()
file(WRITE "${OUTPUT}" "/* No libpng symbol prefix configured. */")
endif()
elseif(OUTPUT MATCHES "(scripts/pnglibconf\\.h\\.prebuilt)\$")
# Generate scripts/pnglibconf.h.prebuilt (fails build)
message(STATUS "Attempting to build scripts/pnglibconf.h.prebuilt")
message(STATUS "This is a machine generated file, but if you want to make")
message(STATUS "a new one simply build the 'png_genfiles' target, and copy")
message(STATUS "scripts/pnglibconf.out to scripts/pnglibconf.h.prebuilt")
message(STATUS "AND set PNG_ZLIB_VERNUM to 0 (you MUST do this)")
message(FATAL_ERROR "Stopping build")
else()
message(FATAL_ERROR "Unsupported output: ${OUTPUT}")
endif()