gn: Tweak precompiled_header docs.
Add an entry for precompiled_header_type, and document
GCC-style precompiled headers a bit.
BUG=none
Review-Url: https://codereview.chromium.org/2734523002
Cr-Original-Commit-Position: refs/heads/master@{#454685}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 698727682cc73ad3770d402395d23096f572d3f2
diff --git a/tools/gn/ninja_binary_target_writer_unittest.cc b/tools/gn/ninja_binary_target_writer_unittest.cc
index 381eb39..6ac8146 100644
--- a/tools/gn/ninja_binary_target_writer_unittest.cc
+++ b/tools/gn/ninja_binary_target_writer_unittest.cc
@@ -772,7 +772,6 @@
{
Target pch_target(&pch_settings,
Label(SourceDir("//foo/"), "pch_target"));
- pch_target.config_values().set_precompiled_header("build/precompile.h");
pch_target.config_values().set_precompiled_source(
SourceFile("//build/precompile.h"));
pch_target.config_values().cflags_c().push_back("-std=c99");
diff --git a/tools/gn/variables.cc b/tools/gn/variables.cc
index 3b60c90..66460e9 100644
--- a/tools/gn/variables.cc
+++ b/tools/gn/variables.cc
@@ -1451,18 +1451,31 @@
config applying to this target specifies this value. In addition, the tool
corresponding to the source files must also specify precompiled headers (see
"gn help tool"). The tool will also specify what type of precompiled headers
- to use.
+ to use, by setting precompiled_header_type to either "gcc" or "msvc".
The precompiled header/source variables can be specified on a target or a
config, but must be the same for all configs applying to a given target since
a target can only have one precompiled header.
+ If you use both C and C++ sources, the precompiled header and source file
+ will be compiled once per language. You will want to make sure to wrap C++
+ includes in __cplusplus #ifdefs so the file will compile in C mode.
+
+GCC precompiled headers
+
+ When using GCC-style precompiled headers, "precompiled_source" contains the
+ path of a .h file that is precompiled and then included by all source files
+ in targets that set "precompiled_source".
+
+ The value of "precompiled_header" is not used with GCC-style precompiled
+ headers.
+
MSVC precompiled headers
When using MSVC-style precompiled headers, the "precompiled_header" value is
a string corresponding to the header. This is NOT a path to a file that GN
- recognises, but rather the exact string that appears in quotes after an
- #include line in source code. The compiler will match this string against
+ recognises, but rather the exact string that appears in quotes after
+ an #include line in source code. The compiler will match this string against
includes or forced includes (/FI).
MSVC also requires a source file to compile the header with. This must be
@@ -1470,10 +1483,6 @@
this IS a GN-style file name, and tells GN which source file to compile to
make the .pch file used for subsequent compiles.
- If you use both C and C++ sources, the precompiled header and source file
- will be compiled using both tools. You will want to make sure to wrap C++
- includes in __cplusplus #ifdefs so the file will compile in C mode.
-
For example, if the toolchain specifies MSVC headers:
toolchain("vc_x64") {
@@ -1500,6 +1509,15 @@
...
)";
+const char kPrecompiledHeaderType[] = "precompiled_header_type";
+const char kPrecompiledHeaderType_HelpShort[] =
+ "precompiled_header_type: [string] \"gcc\" or \"msvc\".";
+const char kPrecompiledHeaderType_Help[] =
+ R"(precompiled_header_type: [string] "gcc" or "msvc".
+
+ See "gn help precompiled_header".
+)";
+
const char kPrecompiledSource[] = "precompiled_source";
const char kPrecompiledSource_HelpShort[] =
"precompiled_source: [file name] Source file to precompile.";
@@ -1904,6 +1922,7 @@
INSERT_VARIABLE(OutputPrefixOverride)
INSERT_VARIABLE(Outputs)
INSERT_VARIABLE(PrecompiledHeader)
+ INSERT_VARIABLE(PrecompiledHeaderType)
INSERT_VARIABLE(PrecompiledSource)
INSERT_VARIABLE(ProductType)
INSERT_VARIABLE(Public)
diff --git a/tools/gn/variables.h b/tools/gn/variables.h
index df94b65..2af40c5 100644
--- a/tools/gn/variables.h
+++ b/tools/gn/variables.h
@@ -239,6 +239,10 @@
extern const char kPrecompiledHeader_HelpShort[];
extern const char kPrecompiledHeader_Help[];
+extern const char kPrecompiledHeaderType[];
+extern const char kPrecompiledHeaderType_HelpShort[];
+extern const char kPrecompiledHeaderType_Help[];
+
extern const char kPrecompiledSource[];
extern const char kPrecompiledSource_HelpShort[];
extern const char kPrecompiledSource_Help[];
