auto generate msvc pch source file if none is provided by the user

docs/markdown/Precompiled-headers.md

@@ -75,8 +75,11 @@ executable('multilang', sources : srclist,
 
 Using precompiled headers with MSVC
 --
+Since Meson version 0.50.0, precompiled headers with MSVC work just like
+with GCC. Meson will automatically create the matching pch implementation
+file for you.
 
-MSVC is a bit trickier, because in addition to the header file, it
+Before version 0.50.0, in addition to the header file, Meson
 also requires a corresponding source file. If your header is called
 `foo_pch.h`, the corresponding source file is usually called
 `foo_pch.cpp` and it resides in the same `pch` subdirectory as the

mesonbuild/backend/backends.py

@@ -515,6 +515,23 @@ class Backend:
             args += compiler.get_pch_use_args(pchpath, p[0])
         return includeargs + args
 
+    def create_msvc_pch_implementation(self, target, lang, pch_header):
+        # We have to include the language in the file name, otherwise
+        # pch.c and pch.cpp will both end up as pch.obj in VS backends.
+        impl_name = 'meson_pch-%s.%s' % (lang, lang)
+        pch_rel_to_build = os.path.join(self.get_target_private_dir(target), impl_name)
+        # Make sure to prepend the build dir, since the working directory is
+        # not defined. Otherwise, we might create the file in the wrong path.
+        pch_file = os.path.join(self.build_dir, pch_rel_to_build)
+        os.makedirs(os.path.dirname(pch_file), exist_ok=True)
+
+        content = '#include "%s"' % os.path.basename(pch_header)
+        pch_file_tmp = pch_file + '.tmp'
+        with open(pch_file_tmp, 'w') as f:
+            f.write(content)
+        mesonlib.replace_if_different(pch_file, pch_file_tmp)
+        return pch_rel_to_build
+
     @staticmethod
     def escape_extra_args(compiler, args):
         # No extra escaping/quoting needed when not running on Windows

mesonbuild/backend/ninjabackend.py

@@ -2252,22 +2252,28 @@ rule FORTRAN_DEP_HACK%s
         return [os.path.join(self.get_target_dir(lt), lt.get_filename()) for lt in target.link_targets]
 
     def generate_msvc_pch_command(self, target, compiler, pch):
-        if len(pch) != 2:
-            raise MesonException('MSVC requires one header and one source to produce precompiled headers.')
         header = pch[0]
-        source = pch[1]
         pchname = compiler.get_pch_name(header)
         dst = os.path.join(self.get_target_private_dir(target), pchname)
 
         commands = []
         commands += self.generate_basic_compiler_args(target, compiler)
+
+        if len(pch) == 1:
+            # Auto generate PCH.
+            source = self.create_msvc_pch_implementation(target, compiler.get_language(), pch[0])
+            pch_header_dir = os.path.dirname(os.path.join(self.build_to_src, target.get_source_subdir(), header))
+            commands += compiler.get_include_args(pch_header_dir, False)
+        else:
+            source = os.path.join(self.build_to_src, target.get_source_subdir(), pch[1])
+
         just_name = os.path.basename(header)
         (objname, pch_args) = compiler.gen_pch_args(just_name, source, dst)
         commands += pch_args
         commands += self._generate_single_compile(target, compiler)
         commands += self.get_compile_debugfile_args(compiler, target, objname)
         dep = dst + '.' + compiler.get_depfile_suffix()
-        return commands, dep, dst, [objname]
+        return commands, dep, dst, [objname], source
 
     def generate_gcc_pch_command(self, target, compiler, pch):
         commands = self._generate_single_compile(target, compiler)
@@ -2296,8 +2302,7 @@ rule FORTRAN_DEP_HACK%s
                 raise InvalidArguments(msg)
             compiler = target.compilers[lang]
             if isinstance(compiler, VisualStudioCCompiler):
-                src = os.path.join(self.build_to_src, target.get_source_subdir(), pch[-1])
-                (commands, dep, dst, objs) = self.generate_msvc_pch_command(target, compiler, pch)
+                (commands, dep, dst, objs, src) = self.generate_msvc_pch_command(target, compiler, pch)
                 extradep = os.path.join(self.build_to_src, target.get_source_subdir(), pch[0])
             elif compiler.id == 'intel':
                 # Intel generates on target generation

mesonbuild/backend/vs2010backend.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import copy
 import os
 import pickle
 import xml.dom.minidom
@@ -1035,13 +1036,18 @@ class Vs2010Backend(backends.Backend):
                     continue
                 pch_node.text = 'Use'
                 if compiler.id == 'msvc':
-                    if len(pch) != 2:
-                        raise MesonException('MSVC requires one header and one source to produce precompiled headers.')
-                    pch_sources[lang] = [pch[0], pch[1], lang]
+                    if len(pch) == 1:
+                        # Auto generate PCH.
+                        src = os.path.join(down, self.create_msvc_pch_implementation(target, lang, pch[0]))
+                        pch_header_dir = os.path.dirname(os.path.join(proj_to_src_dir, pch[0]))
+                    else:
+                        src = os.path.join(proj_to_src_dir, pch[1])
+                        pch_header_dir = None
+                    pch_sources[lang] = [pch[0], src, lang, pch_header_dir]
                 else:
                     # I don't know whether its relevant but let's handle other compilers
                     # used with a vs backend
-                    pch_sources[lang] = [pch[0], None, lang]
+                    pch_sources[lang] = [pch[0], None, lang, None]
         if len(pch_sources) == 1:
             # If there is only 1 language with precompiled headers, we can use it for the entire project, which
             # is cleaner than specifying it for each source file.
@@ -1205,14 +1211,19 @@ class Vs2010Backend(backends.Backend):
                 self.add_preprocessor_defines(lang, inc_cl, file_defines)
                 self.add_include_dirs(lang, inc_cl, file_inc_dirs)
             for lang in pch_sources:
-                header, impl, suffix = pch_sources[lang]
+                impl = pch_sources[lang][1]
                 if impl:
-                    relpath = os.path.join(proj_to_src_dir, impl)
-                    inc_cl = ET.SubElement(inc_src, 'CLCompile', Include=relpath)
+                    inc_cl = ET.SubElement(inc_src, 'CLCompile', Include=impl)
                     self.create_pch(pch_sources, lang, inc_cl)
                     self.add_additional_options(lang, inc_cl, file_args)
                     self.add_preprocessor_defines(lang, inc_cl, file_defines)
-                    self.add_include_dirs(lang, inc_cl, file_inc_dirs)
+                    pch_header_dir = pch_sources[lang][3]
+                    if pch_header_dir:
+                        inc_dirs = copy.deepcopy(file_inc_dirs)
+                        inc_dirs[lang] = [pch_header_dir] + inc_dirs[lang]
+                    else:
+                        inc_dirs = file_inc_dirs
+                    self.add_include_dirs(lang, inc_cl, inc_dirs)
 
         if self.has_objects(objects, additional_objects, gen_objs):
             inc_objs = ET.SubElement(root, 'ItemGroup')

mesonbuild/build.py

@@ -1096,6 +1096,8 @@ You probably should put it in link_with instead.''')
 
             if (os.path.dirname(pchlist[0]) != os.path.dirname(pchlist[1])):
                 raise InvalidArguments('PCH files must be stored in the same folder.')
+
+            mlog.warning('PCH source files are deprecated, only a single header file should be used.')
         elif len(pchlist) > 2:
             raise InvalidArguments('PCH definition may have a maximum of 2 files.')
         for f in pchlist:

test cases/common/13 pch/c/meson.build

@@ -5,4 +5,4 @@ if cc_id == 'lcc'
 endif
 
 exe = executable('prog', 'prog.c',
-c_pch : ['pch/prog_pch.c', 'pch/prog.h'])
+c_pch : 'pch/prog.h')

test cases/common/13 pch/c/pch/prog_pch.c

@@ -1,5 +0,0 @@
-#if !defined(_MSC_VER)
-#error "This file is only for use with MSVC."
-#endif
-
-#include "prog.h"

test cases/common/13 pch/cpp/meson.build

@@ -1 +1 @@
-exe = executable('prog', 'prog.cc', cpp_pch : ['pch/prog.hh', 'pch/prog_pch.cc'])
+exe = executable('prog', 'prog.cc', cpp_pch : 'pch/prog.hh')

test cases/common/13 pch/cpp/pch/prog_pch.cc

@@ -1,5 +0,0 @@
-#if !defined(_MSC_VER)
-#error "This file is only for use with MSVC."
-#endif
-
-#include "prog.hh"

test cases/common/13 pch/generated/meson.build

@@ -13,4 +13,4 @@ generated_generator = generator(find_program('gen_generator.py'),
   arguments: ['@INPUT@', '@OUTPUT@'])
 
 exe = executable('prog', 'prog.c', generated_customTarget, generated_generator.process('generated_generator.in'),
-  c_pch: ['pch/prog_pch.c', 'pch/prog.h'])
+  c_pch: 'pch/prog.h')

test cases/common/13 pch/generated/pch/prog_pch.c

@@ -1,5 +0,0 @@
-#if !defined(_MSC_VER)
-#error "This file is only for use with MSVC."
-#endif
-
-#include "prog.h"

test cases/common/13 pch/meson.build

@@ -3,6 +3,7 @@ project('pch test', 'c', 'cpp')
 subdir('c')
 subdir('cpp')
 subdir('generated')
+subdir('userDefined')
 subdir('withIncludeDirectories')
 
 if meson.backend() == 'xcode'

test cases/common/13 pch/mixed/meson.build

@@ -1,17 +1,6 @@
 exe = executable(
   'prog',
   files('main.cc', 'func.c'),
-  c_pch : ['pch/func.h', 'pch/func_pch.c'],
-  cpp_pch : ['pch/main_pch.cc', 'pch/main.h'],
+  c_pch : ['pch/func.h'],
+  cpp_pch : ['pch/main.h'],
 )
-
-# test pch when only a header is given (not supported by msvc)
-cc = meson.get_compiler('c')
-if not ['msvc', 'clang-cl'].contains(cc.get_id())
-  exe2 = executable(
-    'prog2',
-    files('main.cc', 'func.c'),
-    c_pch : 'pch/func.h',
-    cpp_pch : 'pch/main.h',
-  )
-endif

test cases/common/13 pch/mixed/pch/func_pch.c

@@ -1 +0,0 @@
-#include"func.h"

test cases/common/13 pch/mixed/pch/main_pch.cc

@@ -1 +0,0 @@
-#include"main.h"

test cases/common/13 pch/userDefined/meson.build

@@ -0,0 +1,10 @@
+cc = meson.get_compiler('c')
+cc_id = cc.get_id()
+
+# User supplied PCH implementation should override the auto
+# generated one. PCH implementations are only supported for
+# msvc and generally should not be used at all. Support for
+# them is only kept for backwards compatibility.
+if cc_id == 'msvc'
+  exe = executable('prog', 'prog.c', c_pch : ['pch/pch.h', 'pch/pch.c'])
+endif

test cases/common/13 pch/userDefined/pch/pch.c

@@ -0,0 +1,5 @@
+#include "pch.h"
+
+int foo() {
+    return 0;
+}

test cases/common/13 pch/userDefined/pch/pch.h

@@ -0,0 +1 @@
+int foo();

test cases/common/13 pch/userDefined/prog.c

@@ -0,0 +1,8 @@
+// No includes here, they need to come from the PCH
+
+int main(int argc, char **argv) {
+    // Method is implemented in pch.c.
+    // This makes sure that we can properly handle user defined
+    // pch implementation files and not only auto-generated ones.
+    return foo();
+}

test cases/common/13 pch/withIncludeDirectories/meson.build

@@ -6,4 +6,4 @@ endif
 
 exe = executable('prog', 'prog.c',
   include_directories: 'include',
-  c_pch : ['pch/prog_pch.c', 'pch/prog.h'])
+  c_pch : 'pch/prog.h')

test cases/common/13 pch/withIncludeDirectories/pch/prog_pch.c

@@ -1,5 +0,0 @@
-#if !defined(_MSC_VER)
-#error "This file is only for use with MSVC."
-#endif
-
-#include "prog.h"