Honor CMAKE_<LANG>_FLAGS[_<CONFIG>]_INIT set in toolchain files

Document these variables.

Change our convention for setting these variables from:

    set(CMAKE_C_FLAGS_INIT "...")

to

    string(APPEND CMAKE_C_FLAGS_INIT " ...")

so that any value previously set by a toolchain file will be used.

Automate the conversion with:

    sed -i 's/set *(\(CMAKE_\(C\|CXX\|Fortran\|RC\|ASM\|${[^}]\+}\)_FLAGS\(_[^_]\+\)\?_INIT \+"\)/string(APPEND \1 /' \
      Modules/Compiler/*.cmake Modules/Platform/*.cmake

and follow up with some manual fixes (e.g. to cases that already
meant to append).  Also revert the automated changes to contexts
that are not protected from running multiple times.

Help/manual/cmake-variables.7.rst

@@ -344,10 +344,15 @@ Variables for Languages
    /variable/CMAKE_LANG_CREATE_SHARED_MODULE
    /variable/CMAKE_LANG_CREATE_STATIC_LIBRARY
    /variable/CMAKE_LANG_FLAGS_DEBUG
+   /variable/CMAKE_LANG_FLAGS_DEBUG_INIT
    /variable/CMAKE_LANG_FLAGS_MINSIZEREL
+   /variable/CMAKE_LANG_FLAGS_MINSIZEREL_INIT
    /variable/CMAKE_LANG_FLAGS_RELEASE
+   /variable/CMAKE_LANG_FLAGS_RELEASE_INIT
    /variable/CMAKE_LANG_FLAGS_RELWITHDEBINFO
+   /variable/CMAKE_LANG_FLAGS_RELWITHDEBINFO_INIT
    /variable/CMAKE_LANG_FLAGS
+   /variable/CMAKE_LANG_FLAGS_INIT
    /variable/CMAKE_LANG_GHS_KERNEL_FLAGS_DEBUG
    /variable/CMAKE_LANG_GHS_KERNEL_FLAGS_MINSIZEREL
    /variable/CMAKE_LANG_GHS_KERNEL_FLAGS_RELEASE

Help/release/dev/toolchain-flag-init.rst

+toolchain-flag-init
+-------------------
+
+* :variable:`Toolchain files <CMAKE_TOOLCHAIN_FILE>` may now set a
+  :variable:`CMAKE_<LANG>_FLAGS_INIT` variable to initialize the
+  :variable:`CMAKE_<LANG>_FLAGS` cache entry the first time a language is
+  enabled in a build tree.

Help/variable/CMAKE_LANG_FLAGS_DEBUG_INIT.rst

+CMAKE_<LANG>_FLAGS_DEBUG_INIT
+-----------------------------
+
+Value used to initialize the :variable:`CMAKE_<LANG>_FLAGS_DEBUG` cache
+entry the first time a build tree is configured for language ``<LANG>``.
+This variable is meant to be set by a :variable:`toolchain file
+<CMAKE_TOOLCHAIN_FILE>`.  CMake may prepend or append content to
+the value based on the environment and target platform.
+
+See also :variable:`CMAKE_<LANG>_FLAGS_INIT`.

Help/variable/CMAKE_LANG_FLAGS_INIT.rst

+CMAKE_<LANG>_FLAGS_INIT
+-----------------------
+
+Value used to initialize the :variable:`CMAKE_<LANG>_FLAGS` cache entry
+the first time a build tree is configured for language ``<LANG>``.
+This variable is meant to be set by a :variable:`toolchain file
+<CMAKE_TOOLCHAIN_FILE>`.  CMake may prepend or append content to
+the value based on the environment and target platform.
+
+See also the configuration-specific variables:
+
+* :variable:`CMAKE_<LANG>_FLAGS_DEBUG_INIT`
+* :variable:`CMAKE_<LANG>_FLAGS_RELEASE_INIT`
+* :variable:`CMAKE_<LANG>_FLAGS_MINSIZEREL_INIT`
+* :variable:`CMAKE_<LANG>_FLAGS_RELWITHDEBINFO_INIT`

Help/variable/CMAKE_LANG_FLAGS_MINSIZEREL_INIT.rst

+CMAKE_<LANG>_FLAGS_MINSIZEREL_INIT
+----------------------------------
+
+Value used to initialize the :variable:`CMAKE_<LANG>_FLAGS_MINSIZEREL`
+cache entry the first time a build tree is configured for language ``<LANG>``.
+This variable is meant to be set by a :variable:`toolchain file
+<CMAKE_TOOLCHAIN_FILE>`.  CMake may prepend or append content to
+the value based on the environment and target platform.
+
+See also :variable:`CMAKE_<LANG>_FLAGS_INIT`.

Help/variable/CMAKE_LANG_FLAGS_RELEASE_INIT.rst

+CMAKE_<LANG>_FLAGS_RELEASE_INIT
+-------------------------------
+
+Value used to initialize the :variable:`CMAKE_<LANG>_FLAGS_RELEASE`
+cache entry the first time a build tree is configured for language ``<LANG>``.
+This variable is meant to be set by a :variable:`toolchain file
+<CMAKE_TOOLCHAIN_FILE>`.  CMake may prepend or append content to
+the value based on the environment and target platform.
+
+See also :variable:`CMAKE_<LANG>_FLAGS_INIT`.

Help/variable/CMAKE_LANG_FLAGS_RELWITHDEBINFO_INIT.rst

+CMAKE_<LANG>_FLAGS_RELWITHDEBINFO_INIT
+--------------------------------------
+
+Value used to initialize the :variable:`CMAKE_<LANG>_FLAGS_RELWITHDEBINFO`
+cache entry the first time a build tree is configured for language ``<LANG>``.
+This variable is meant to be set by a :variable:`toolchain file
+<CMAKE_TOOLCHAIN_FILE>`.  CMake may prepend or append content to
+the value based on the environment and target platform.
+
+See also :variable:`CMAKE_<LANG>_FLAGS_INIT`.

Help/variable/CMAKE_USER_MAKE_RULES_OVERRIDE.rst

@@ -14,8 +14,10 @@ variables that must be set before CMake builds its first test project
 to check that the compiler for a language works.  It should not be
 used to load a file in cases that a normal :command:`include` will work.  Use
 it only as a last resort for behavior that cannot be achieved any
-other way.  For example, one may set ``CMAKE_C_FLAGS_INIT`` to change the
-default value used to initialize :variable:`CMAKE_C_FLAGS <CMAKE_<LANG>_FLAGS>`
+other way.  For example, one may set the
+:variable:`CMAKE_C_FLAGS_INIT <CMAKE_<LANG>_FLAGS_INIT>` variable
+to change the default value used to initialize the
+:variable:`CMAKE_C_FLAGS <CMAKE_<LANG>_FLAGS>` variable
 before it is cached.  The override file should NOT be used to set anything
 that could be set after languages are enabled, such as variables like
 :variable:`CMAKE_RUNTIME_OUTPUT_DIRECTORY` that affect the placement of

Modules/Compiler/ARMCC.cmake

@@ -20,11 +20,11 @@ set(CMAKE_AR "${CMAKE_ARMCC_AR}" CACHE FILEPATH "The ARMCC archiver" FORCE)
 mark_as_advanced(CMAKE_ARMCC_AR)
 
 macro(__compiler_armcc lang)
-  set(CMAKE_${lang}_FLAGS_INIT "")
-  set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-g")
-  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-Ospace -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-Otime -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
+  string(APPEND CMAKE_${lang}_FLAGS_INIT " ")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -Ospace -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -Otime -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -O2 -g")
 
   set(CMAKE_${lang}_OUTPUT_EXTENSION ".o")
   set(CMAKE_${lang}_OUTPUT_EXTENSION_REPLACE 1)

Modules/Compiler/Absoft-Fortran.cmake

-set(CMAKE_Fortran_FLAGS_INIT "")
-set(CMAKE_Fortran_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_Fortran_FLAGS_MINSIZEREL_INIT "")
-set(CMAKE_Fortran_FLAGS_RELEASE_INIT "-O3")
-set(CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
+string(APPEND CMAKE_Fortran_FLAGS_INIT " ")
+string(APPEND CMAKE_Fortran_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_Fortran_FLAGS_MINSIZEREL_INIT " ")
+string(APPEND CMAKE_Fortran_FLAGS_RELEASE_INIT " -O3")
+string(APPEND CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT " -O2 -g")
 set(CMAKE_Fortran_MODDIR_FLAG "-YMOD_OUT_DIR=")
 set(CMAKE_Fortran_MODPATH_FLAG "-p")
 set(CMAKE_Fortran_VERBOSE_FLAG "-v")

Modules/Compiler/Bruce-C.cmake

 # Bruce C Compiler ignores "-g" flag and optimization cannot be
 # enabled here (it is implemented only for 8086 target).
-set (CMAKE_C_FLAGS_INIT "-D__CLASSIC_C__")
-set (CMAKE_C_FLAGS_DEBUG_INIT "-g")
-set (CMAKE_C_FLAGS_MINSIZEREL_INIT "-DNDEBUG")
-set (CMAKE_C_FLAGS_RELEASE_INIT "-DNDEBUG")
-set (CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-g -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_INIT " -D__CLASSIC_C__")
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELWITHDEBINFO_INIT " -g -DNDEBUG")

Modules/Compiler/G95-Fortran.cmake

-set(CMAKE_Fortran_FLAGS_INIT "")
-set(CMAKE_Fortran_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_Fortran_FLAGS_MINSIZEREL_INIT "-Os")
-set(CMAKE_Fortran_FLAGS_RELEASE_INIT "-O3")
-set(CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
+string(APPEND CMAKE_Fortran_FLAGS_INIT " ")
+string(APPEND CMAKE_Fortran_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_Fortran_FLAGS_MINSIZEREL_INIT " -Os")
+string(APPEND CMAKE_Fortran_FLAGS_RELEASE_INIT " -O3")
+string(APPEND CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT " -O2 -g")
 set(CMAKE_Fortran_MODDIR_FLAG "-fmod=")
 set(CMAKE_Fortran_VERBOSE_FLAG "-v")
 set(CMAKE_Fortran_FORMAT_FIXED_FLAG "-ffixed-form")

Modules/Compiler/GHS-C.cmake

@@ -3,11 +3,11 @@ include(Compiler/GHS)
 set(CMAKE_C_VERBOSE_FLAG "-v")
 set(CMAKE_C_OUTPUT_EXTENSION ".o")
 
-set(CMAKE_C_FLAGS_INIT "")
-set(CMAKE_C_FLAGS_DEBUG_INIT "-Odebug -g")
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "-Ospace")
-set(CMAKE_C_FLAGS_RELEASE_INIT "-O")
-set(CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-O -g")
+string(APPEND CMAKE_C_FLAGS_INIT " ")
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " -Odebug -g")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -Ospace")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -O")
+string(APPEND CMAKE_C_FLAGS_RELWITHDEBINFO_INIT " -O -g")
 
 set(CMAKE_C_GHS_KERNEL_FLAGS_DEBUG_INIT "-ldebug ${CMAKE_C_FLAGS_DEBUG_INIT}")
 set(CMAKE_C_GHS_KERNEL_FLAGS_MINSIZEREL_INIT "${CMAKE_C_FLAGS_MINSIZEREL_INIT}")

Modules/Compiler/GHS-CXX.cmake

@@ -3,11 +3,11 @@ include(Compiler/GHS)
 set(CMAKE_CXX_VERBOSE_FLAG "-v")
 set(CMAKE_CXX_OUTPUT_EXTENSION ".o")
 
-set(CMAKE_CXX_FLAGS_INIT "")
-set(CMAKE_CXX_FLAGS_DEBUG_INIT "-Odebug -g")
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "-Ospace")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "-O")
-set(CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT "-O -g")
+string(APPEND CMAKE_CXX_FLAGS_INIT " ")
+string(APPEND CMAKE_CXX_FLAGS_DEBUG_INIT " -Odebug -g")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " -Ospace")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " -O")
+string(APPEND CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT " -O -g")
 
 set(CMAKE_CXX_GHS_KERNEL_FLAGS_DEBUG_INIT
   "-ldebug ${CMAKE_CXX_FLAGS_DEBUG_INIT}")

Modules/Compiler/GNU-Fortran.cmake

@@ -5,8 +5,8 @@ set(CMAKE_Fortran_FORMAT_FIXED_FLAG "-ffixed-form")
 set(CMAKE_Fortran_FORMAT_FREE_FLAG "-ffree-form")
 
 # No -DNDEBUG for Fortran.
-set(CMAKE_Fortran_FLAGS_MINSIZEREL_INIT "-Os")
-set(CMAKE_Fortran_FLAGS_RELEASE_INIT "-O3")
+string(APPEND CMAKE_Fortran_FLAGS_MINSIZEREL_INIT " -Os")
+string(APPEND CMAKE_Fortran_FLAGS_RELEASE_INIT " -O3")
 
 # No -isystem for Fortran because it will not find .mod files.
 unset(CMAKE_INCLUDE_SYSTEM_FLAG_Fortran)

Modules/Compiler/GNU.cmake

@@ -45,11 +45,11 @@ macro(__compiler_gnu lang)
   endif()
 
   # Initial configuration flags.
-  set(CMAKE_${lang}_FLAGS_INIT "")
-  set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-g")
-  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-Os -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-O3 -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-O2 -g -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_INIT " ")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -Os -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -O3 -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -O2 -g -DNDEBUG")
   set(CMAKE_${lang}_CREATE_PREPROCESSED_SOURCE "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -E <SOURCE> > <PREPROCESSED_SOURCE>")
   set(CMAKE_${lang}_CREATE_ASSEMBLY_SOURCE "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -S <SOURCE> -o <ASSEMBLY_SOURCE>")
   if(NOT APPLE OR NOT CMAKE_${lang}_COMPILER_VERSION VERSION_LESS 4) # work around #4462

Modules/Compiler/Intel.cmake

@@ -27,10 +27,10 @@ else()
   macro(__compiler_intel lang)
     set(CMAKE_${lang}_VERBOSE_FLAG "-v")
 
-    set(CMAKE_${lang}_FLAGS_INIT "")
-    set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-g")
-    set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-Os")
-    set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-O3")
-    set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
+    string(APPEND CMAKE_${lang}_FLAGS_INIT " ")
+    string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g")
+    string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -Os")
+    string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -O3")
+    string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -O2 -g")
   endmacro()
 endif()

Modules/Compiler/PGI-C.cmake

 include(Compiler/PGI)
 __compiler_pgi(C)
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "${CMAKE_C_FLAGS_MINSIZEREL_INIT} -DNDEBUG")
-set(CMAKE_C_FLAGS_RELEASE_INIT "${CMAKE_C_FLAGS_RELEASE_INIT} -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -DNDEBUG")

Modules/Compiler/PGI-CXX.cmake

 include(Compiler/PGI)
 __compiler_pgi(CXX)
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "${CMAKE_CXX_FLAGS_MINSIZEREL_INIT} -DNDEBUG")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "${CMAKE_CXX_FLAGS_RELEASE_INIT} -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " -DNDEBUG")

Modules/Compiler/PGI-Fortran.cmake

@@ -4,7 +4,7 @@ __compiler_pgi(Fortran)
 set(CMAKE_Fortran_FORMAT_FIXED_FLAG "-Mnofreeform")
 set(CMAKE_Fortran_FORMAT_FREE_FLAG "-Mfreeform")
 
-set(CMAKE_Fortran_FLAGS_INIT "${CMAKE_Fortran_FLAGS_INIT} -Mpreprocess -Kieee")
-set(CMAKE_Fortran_FLAGS_DEBUG_INIT "${CMAKE_Fortran_FLAGS_DEBUG_INIT} -Mbounds")
+string(APPEND CMAKE_Fortran_FLAGS_INIT " -Mpreprocess -Kieee")
+string(APPEND CMAKE_Fortran_FLAGS_DEBUG_INIT " -Mbounds")
 
 set(CMAKE_Fortran_MODDIR_FLAG "-module ")