Add documentation for Builtin options and bitcode

Also add a test that ensures that new base options and compiler options
are always documented.

docs/markdown/Builtin-options.md

@@ -0,0 +1,113 @@
+---
+short-description: Built-in options to configure project properties
+...
+
+# Built-in options
+
+Meson provides two kinds of options: [build options provided by the
+build files](Build-options.md) and built-in options that are either
+universal options, base options, compiler options.
+
+## Universal options
+
+A list of these options can be found by running `meson --help`. All
+these can be set by passing to `meson` (aka `meson setup`) in any of
+these ways:
+
+| --option=value |
+| --option value |
+| -Doption=value |
+
+They can also be edited after setup using `meson configure`.
+
+Installation options are all relative to the prefix, except:
+
+* When the prefix is `/usr`: `sysconfdir` defaults to `/etc`, `localstatedir` defaults to `/var`, and `sharedstatedir` defaults to `/var/lib`
+* When the prefix is `/usr/local`: `localstatedir` defaults to `/var/local`, and `sharedstatedir` defaults to `/var/local/lib`
+
+| Option         | Default value | Description
+| ------         | ------------- | -----------
+| prefix         | see below     | Installation prefix
+| libdir         | see below     | Library directory
+| libexecdir     | libexec       | Library executable directory
+| bindir         | bin           | Executable directory
+| sbindir        | sbin          | System executable directory
+| includedir     | include       | Header file directory
+| datadir        | share         | Data file directory
+| mandir         | share/man     | Manual page directory
+| infodir        | share/info    | Info page directory
+| localedir      | share/locale  | Locale data directory
+| sysconfdir     | etc           | Sysconf data directory
+| localstatedir  | var           | Localstate data directory
+| sharedstatedir | com           | Architecture-independent data directory
+
+`prefix` defaults to `C:/` on Windows, and `/usr/local/` otherwise. You should always
+override this value.
+
+`libdir` is automatically detected based on your platform, but the
+implementation is [currently buggy](https://github.com/mesonbuild/meson/issues/2038)
+on Linux platforms.
+
+There are various other options to set, for instance the backend to use and
+the path to the cross-file while cross compiling, which won't be repeated here.
+Please see the output of `meson --help`.
+
+## Base options
+
+These are set in the same way as universal options, but cannot be shown in the
+output of `meson --help` because they depend on both the current platform and
+the compiler that will be selected. The only way to see them is to setup
+a builddir and then run `meson configure` on it with no options.
+
+The following options are available. Note that they may not be available on all
+platforms or with all compilers:
+
+| Option      | Default value | Possible values         | Description
+| ----------- | ------------- | ---------------         | -----------
+| b_asneeded  | true          | true, false             | Use -Wl,--as-needed when linking
+| b_bitcode   | false         | true, false             | Embed Apple bitcode, see below
+| b_colorout  | always        | auto, always, never     | Use colored output
+| b_coverage  | false         | true, false             | Enable coverage tracking
+| b_lundef    | true          | true, false             | Don't allow undefined symbols when linking
+| b_lto       | false         | true, false             | Use link time optimization
+| b_ndebug    | false         | true, false, if-release | Disable asserts
+| b_pch       | true          | true, false             | Use precompiled headers
+| b_pgo       | off           | off, generate, use      | Use profile guided optimization
+| b_sanitize  | none          | see below               | Code sanitizer to use
+| b_staticpic | true          | true, false             | Build static libraries as position independent
+
+The value of `b_sanitize` can be one of: `none`, `address`, `thread`,
+`undefined`, `memory`, `address,undefined`.
+
+### Notes about Apple Bitcode support
+
+`b_bitcode` will pass `-fembed-bitcode` while compiling and will pass
+`-Wl,-bitcode_bundle` while linking. These options are incompatible with
+`b_asneeded`, so that option will be silently disabled.
+
+[Shared modules](#Reference-manual.md#shared_module) will not have bitcode
+embedded because `-Wl,-bitcode_bundle` is incompatible with both `-bundle` and
+`-Wl,-undefined,dynamic_lookup` which are necessary for shared modules to work.
+
+## Compiler options
+
+Same caveats as base options above.
+
+The following options are available. Note that both the options themselves and
+the possible values they can take will depend on the target platform or
+compiler being used:
+
+| Option       | Default value | Possible values                          | Description
+| ------       | ------------- | ---------------                          | -----------
+| c_args       |               | free-form comma-separated list           | C compile arguments to use
+| c_std        | none          | none, c89, c99, c11, gnu89, gnu99, gnu11 | C language standard to use
+| c_winlibs    | see below     | free-form comma-separated list           | Standard Windows libs to link against
+| cpp_args     |               | free-form comma-separated list           | C++ compile arguments to use
+| cpp_std      | none          | none, c++98, c++03, c++11, c++14, c++17, <br/>c++1z, gnu++03, gnu++11, gnu++14, gnu++17, gnu++1z | C++ language standard to use
+| cpp_debugstl | false         | true, false                              | C++ STL debug mode
+| cpp_eh       | sc            | none, a, s, sc                           | C++ exception handling type
+| cpp_winlibs  | see below     | free-form comma-separated list           | Standard Windows libs to link against
+
+The default values of `c_winlibs` and `cpp_winlibs` are in compiler-specific
+argument forms, but the libraries are: kernel32, user32, gdi32, winspool,
+shell32, ole32, oleaut32, uuid, comdlg32, advapi32

docs/markdown/snippets/bitcode_support.md

@@ -0,0 +1,15 @@
+## New base build option for LLVM (Apple) bitcode support
+
+When building with clang on macOS, you can now build your static and shared
+binaries with embedded bitcode by enabling the `b_bitcode` [base
+option](Builtin-options.md#Base_options) by passing `-Db_bitcode=true` to
+Meson.
+
+This is better than passing the options manually in the environment since Meson
+will automatically disable conflicting options such as `b_asneeded`, and will
+disable bitcode support on targets that don't support it such as
+`shared_module()`.
+
+Since this requires support in the linker, it is currently only enabled when
+using Apple ld. In the future it can be extended to clang on other platforms
+too.

run_unittests.py

@@ -2113,6 +2113,27 @@ recommended as it can lead to undefined behaviour on some platforms''')
         self.assertEqual(obj.builtins['default_library'].value, 'shared')
         self.wipe()
 
+    def test_compiler_options_documented(self):
+        '''
+        Test that C and C++ compiler options and base options are documented in
+        Builtin-Options.md. Only tests the default compiler for the current
+        platform on the CI.
+        '''
+        md = None
+        with open('docs/markdown/Builtin-options.md') as f:
+            md = f.read()
+        self.assertIsNotNone(md)
+        env = Environment('.', self.builddir, get_fake_options(self.prefix), [])
+        # FIXME: Support other compilers
+        cc = env.detect_c_compiler(False)
+        cpp = env.detect_cpp_compiler(False)
+        for comp in (cc, cpp):
+            for opt in comp.get_options().keys():
+                self.assertIn(opt, md)
+            for opt in comp.base_options:
+                self.assertIn(opt, md)
+        self.assertNotIn('b_unknown', md)
+
 
 class FailureTests(BasePlatformTests):
     '''