MSVC: Add abstraction for debug information format

Replace our hard-coded default for `/Zi` with a first-class abstraction
to select the debug information format an enumeration of logical
names.  We've long hesitated to do this because the idea of "debug
information format" touches on related concepts on several platforms.
Avoid that scope creep by simply defining an abstraction that applies
only when targeting the MSVC ABI on Windows.

Removing the old default flag requires a policy because existing
projects may rely on string processing to edit them and choose a
runtime library under the old behavior.  Add policy CMP0141 to
provide compatibility.

Fixes: #10189

9 files changed, 154 insertions, 0 deletions

diff --git a/Help/command/try_compile.rst b/Help/command/try_compile.rst
index 73dd9d3..710fd21 100644
--- a/Help/command/try_compile.rst
+++ b/Help/command/try_compile.rst
@@ -244,3 +244,8 @@ a build configuration.
 .. versionadded:: 3.24
   The :variable:`CMAKE_TRY_COMPILE_NO_PLATFORM_VARIABLES` variable may be
   set to disable passing platform variables into the test project.
+
+.. versionadded:: 3.25
+  If :policy:`CMP0141` is set to ``NEW``, one can use
+  :variable:`CMAKE_MSVC_DEBUG_INFORMATION_FORMAT` to specify MSVC debug
+  information format.
diff --git a/Help/manual/cmake-policies.7.rst b/Help/manual/cmake-policies.7.rst
index a1133b9..c0c37d1 100644
--- a/Help/manual/cmake-policies.7.rst
+++ b/Help/manual/cmake-policies.7.rst
@@ -58,6 +58,7 @@ Policies Introduced by CMake 3.25
 .. toctree::
    :maxdepth: 1
 
+   CMP0141: MSVC debug information format flags are selected by an abstraction. </policy/CMP0141>
    CMP0140: The return() command checks its arguments. </policy/CMP0140>
 
 Policies Introduced by CMake 3.24
diff --git a/Help/manual/cmake-properties.7.rst b/Help/manual/cmake-properties.7.rst
index d98f7cc..09c3c88 100644
--- a/Help/manual/cmake-properties.7.rst
+++ b/Help/manual/cmake-properties.7.rst
@@ -340,6 +340,7 @@ Properties on Targets
    /prop_tgt/MACOSX_RPATH
    /prop_tgt/MANUALLY_ADDED_DEPENDENCIES
    /prop_tgt/MAP_IMPORTED_CONFIG_CONFIG
+   /prop_tgt/MSVC_DEBUG_INFORMATION_FORMAT
    /prop_tgt/MSVC_RUNTIME_LIBRARY
    /prop_tgt/NAME
    /prop_tgt/NO_SONAME
diff --git a/Help/manual/cmake-variables.7.rst b/Help/manual/cmake-variables.7.rst
index ad6bfbc..02706d8 100644
--- a/Help/manual/cmake-variables.7.rst
+++ b/Help/manual/cmake-variables.7.rst
@@ -486,6 +486,7 @@ Variables that Control the Build
    /variable/CMAKE_MODULE_LINKER_FLAGS_CONFIG_INIT
    /variable/CMAKE_MODULE_LINKER_FLAGS_INIT
    /variable/CMAKE_MSVCIDE_RUN_PATH
+   /variable/CMAKE_MSVC_DEBUG_INFORMATION_FORMAT
    /variable/CMAKE_MSVC_RUNTIME_LIBRARY
    /variable/CMAKE_NINJA_OUTPUT_PATH_PREFIX
    /variable/CMAKE_NO_BUILTIN_CHRPATH
diff --git a/Help/policy/CMP0141.rst b/Help/policy/CMP0141.rst
new file mode 100644
index 0000000..51fa5fd
--- /dev/null
+++ b/Help/policy/CMP0141.rst
@@ -0,0 +1,55 @@
+CMP0141
+-------
+
+.. versionadded:: 3.25
+
+MSVC debug information format flags are selected by an abstraction.
+
+Compilers targeting the MSVC ABI have flags to select the debug information
+format. Debug information format selection typically varies with build
+configuration.
+
+In CMake 3.24 and below, debug information format flags are added to
+the default :variable:`CMAKE_<LANG>_FLAGS_<CONFIG>` cache entries by CMake
+automatically.  This allows users to edit their cache entries to adjust the
+flags.  However, the presence of such default flags is problematic for
+projects that want to choose a different runtime library programmatically.
+In particular, it requires string editing of the
+:variable:`CMAKE_<LANG>_FLAGS_<CONFIG>` variables with knowledge of the
+CMake builtin defaults so they can be replaced.
+
+CMake 3.25 and above prefer to leave the debug information format flags
+out of the default :variable:`CMAKE_<LANG>_FLAGS_<CONFIG>` values and instead
+offer a first-class abstraction.  The
+:variable:`CMAKE_MSVC_DEBUG_INFORMATION_FORMAT` variable and
+:prop_tgt:`MSVC_DEBUG_INFORMATION_FORMAT` target property may be set to
+select the MSVC debug information format.  If they are not set, CMake
+enables debug information in debug configurations using the default value
+``$<$<CONFIG:Debug,RelWithDebInfo>:ProgramDatabase>``, if supported by the
+compiler, and otherwise ``$<$<CONFIG:Debug,RelWithDebInfo>:Embedded>``.
+
+This policy provides compatibility with projects that have not been updated
+to be aware of the abstraction.  The policy setting takes effect as of the
+first :command:`project` or :command:`enable_language` command that enables
+a language whose compiler targets the MSVC ABI.
+
+.. note::
+
+  Once the policy has taken effect at the top of a project, that choice
+  will be used throughout the tree.  In projects that have nested projects
+  in subdirectories, be sure to confirm if everything is working with the
+  selected policy behavior.
+
+The ``OLD`` behavior for this policy is to place MSVC debug information
+format flags in the default :variable:`CMAKE_<LANG>_FLAGS_<CONFIG>` cache
+entries and ignore the :variable:`CMAKE_MSVC_DEBUG_INFORMATION_FORMAT`
+abstraction.  The ``NEW`` behavior for this policy is to *not* place MSVC
+debug information format flags flags in the default cache entries and use
+the abstraction instead.
+
+This policy was introduced in CMake version 3.25.  Use the
+:command:`cmake_policy` command to set it to ``OLD`` or ``NEW`` explicitly.
+Unlike many policies, CMake version |release| does *not* warn
+when this policy is not set and simply uses ``OLD`` behavior.
+
+.. include:: DEPRECATED.txt
diff --git a/Help/prop_tgt/MSVC_DEBUG_INFORMATION_FORMAT-VALUES.txt b/Help/prop_tgt/MSVC_DEBUG_INFORMATION_FORMAT-VALUES.txt
new file mode 100644
index 0000000..9a68460
--- /dev/null
+++ b/Help/prop_tgt/MSVC_DEBUG_INFORMATION_FORMAT-VALUES.txt
@@ -0,0 +1,15 @@
+``Embedded``
+  Compile with ``-Z7`` or equivalent flag(s) to produce object files
+  with full symbolic debugging information.
+``ProgramDatabase``
+  Compile with ``-Zi`` or equivalent flag(s) to produce a program
+  database that contains all the symbolic debugging information.
+``EditAndContinue``
+  Compile with ``-ZI`` or equivalent flag(s) to produce a program
+  database that supports the Edit and Continue feature.
+
+The value is ignored on non-MSVC compilers but an unsupported value will
+be rejected as an error when using a compiler targeting the MSVC ABI.
+
+The value may also be the empty string (``""``) in which case no debug
+information format flag will be added explicitly by CMake.
diff --git a/Help/prop_tgt/MSVC_DEBUG_INFORMATION_FORMAT.rst b/Help/prop_tgt/MSVC_DEBUG_INFORMATION_FORMAT.rst
new file mode 100644
index 0000000..2314cff
--- /dev/null
+++ b/Help/prop_tgt/MSVC_DEBUG_INFORMATION_FORMAT.rst
@@ -0,0 +1,33 @@
+MSVC_DEBUG_INFORMATION_FORMAT
+-----------------------------
+
+.. versionadded:: 3.25
+
+Select debug information format targeting the MSVC ABI.
+
+The allowed values are:
+
+.. include:: MSVC_DEBUG_INFORMATION_FORMAT-VALUES.txt
+
+Use :manual:`generator expressions <cmake-generator-expressions(7)>` to
+support per-configuration specification.  For example, the code:
+
+.. code-block:: cmake
+
+  add_executable(foo foo.c)
+  set_property(TARGET foo PROPERTY
+    MSVC_DEBUG_INFORMATION_FORMAT "$<$<CONFIG:Debug,RelWithDebInfo>:ProgramDatabase>")
+
+selects for the target ``foo`` the program database debug information format
+for the Debug configuration.
+
+If this property is not set, CMake selects a debug information format using
+the default value ``$<$<CONFIG:Debug,RelWithDebInfo>:ProgramDatabase>``, if
+supported by the compiler, and otherwise
+``$<$<CONFIG:Debug,RelWithDebInfo>:Embedded>``.
+
+.. note::
+
+  This property has effect only when policy :policy:`CMP0141` is set to ``NEW``
+  prior to the first :command:`project` or :command:`enable_language` command
+  that enables a language using a compiler targeting the MSVC ABI.
diff --git a/Help/release/dev/MsvcDebugInformationFormatAbstraction.rst b/Help/release/dev/MsvcDebugInformationFormatAbstraction.rst
new file mode 100644
index 0000000..d0c077c
--- /dev/null
+++ b/Help/release/dev/MsvcDebugInformationFormatAbstraction.rst
@@ -0,0 +1,7 @@
+MsvcDebugInformationFormatAbstraction
+-------------------------------------
+
+* The :variable:`CMAKE_MSVC_DEBUG_INFORMATION_FORMAT` variable and
+  :prop_tgt:`MSVC_DEBUG_INFORMATION_FORMAT` target property were introduced
+  to select the debug information format for compilers targeting the MSVC ABI.
+  See policy :policy:`CMP0141`.
diff --git a/Help/variable/CMAKE_MSVC_DEBUG_INFORMATION_FORMAT.rst b/Help/variable/CMAKE_MSVC_DEBUG_INFORMATION_FORMAT.rst
new file mode 100644
index 0000000..80df8fc
--- /dev/null
+++ b/Help/variable/CMAKE_MSVC_DEBUG_INFORMATION_FORMAT.rst
@@ -0,0 +1,36 @@
+CMAKE_MSVC_DEBUG_INFORMATION_FORMAT
+-----------------------------------
+
+.. versionadded:: 3.25
+
+Select the MSVC debug information format targeting the MSVC ABI.
+This variable is used to initialize the
+:prop_tgt:`MSVC_DEBUG_INFORMATION_FORMAT` property on all targets as they are
+created.  It is also propagated by calls to the :command:`try_compile` command
+into the test project.
+
+The allowed values are:
+
+.. include:: ../prop_tgt/MSVC_DEBUG_INFORMATION_FORMAT-VALUES.txt
+
+Use :manual:`generator expressions <cmake-generator-expressions(7)>` to
+support per-configuration specification.  For example, the code:
+
+.. code-block:: cmake
+
+  set(CMAKE_MSVC_DEBUG_INFORMATION_FORMAT "$<$<CONFIG:Debug,RelWithDebInfo>:ProgramDatabase>")
+
+selects for all following targets the program database debug information format
+for the Debug configuration.
+
+If this variable is not set, the :prop_tgt:`MSVC_DEBUG_INFORMATION_FORMAT`
+target property will not be set automatically.  If that property is not set,
+CMake selects a debug information format using the default value
+``$<$<CONFIG:Debug,RelWithDebInfo>:ProgramDatabase>``, if supported by the
+compiler, and otherwise ``$<$<CONFIG:Debug,RelWithDebInfo>:Embedded>``.
+
+.. note::
+
+  This variable has effect only when policy :policy:`CMP0141` is set to ``NEW``
+  prior to the first :command:`project` or :command:`enable_language` command
+  that enables a language using a compiler targeting the MSVC ABI.