envconfig: Autodetect and support BuildCache

Add BuildCache as a supported compiler cache. Also autodetect
the presence of BuildCache as part of detect_compiler_cache().

The order of preference is:

  1. sccache
  2. ccache
  3. buildcache

Thus, when either sccache or ccache is present in the PATH the
compiler cache selection is unaffected by this change.

docs/markdown/Feature-autodetection.md

@@ -23,6 +23,9 @@ changed). Meson will then use the specified compiler without Ccache.
 [sccache](https://github.com/mozilla/sccache) is auto-detected the
 same way, and is preferred over Ccache when both are installed.
 
+[BuildCache](https://gitlab.com/bits-n-bites/buildcache) is
+auto-detected as well, after Ccache and sccache.
+
 [kache](https://github.com/kunobi-ninja/kache) is also supported, but
 is never added automatically: it must be invoked with a compiler
 subcommand (`kache cc`, `kache c++`, ...), so Meson cannot safely

docs/markdown/Machine-files.md

@@ -181,7 +181,7 @@ pkg-config = '/usr/bin/i586-mingw32msvc-pkg-config'
 ```
 
 The compiler may be prefixed with a supported compiler cache wrapper,
-namely ccache, sccache or kache, e.g. `c = ['kache', 'cc']`.
+namely ccache, sccache, kache or buildcache, e.g. `c = ['kache', 'cc']`.
 
 An incomplete list of internally used programs that can be overridden
 here is:

docs/markdown/snippets/buildcache.md

@@ -0,0 +1,7 @@
+## Added support for buildcache
+
+Meson now recognizes [BuildCache](https://gitlab.com/bits-n-bites/buildcache)
+as a compiler wrapper, so setting e.g. `CC="buildcache cc"` works like it
+already does for Ccache and sccache. BuildCache is also auto-detected
+alongside Ccache and sccache, and is used as a fallback after both of those
+when no compiler is specified explicitly.

mesonbuild/envconfig.py

@@ -496,13 +496,20 @@ class BinaryTable:
     def detect_kache() -> ExternalProgram:
         return ExternalProgram('kache', silent=True)
 
+    @staticmethod
+    def detect_buildcache() -> ExternalProgram:
+        return ExternalProgram('buildcache', silent=True)
+
     @staticmethod
     def detect_compiler_cache() -> ExternalProgram:
         # Sccache is "newer" so it is assumed that people would prefer it by default.
         cache = BinaryTable.detect_sccache()
         if cache.found():
             return cache
-        return BinaryTable.detect_ccache()
+        cache = BinaryTable.detect_ccache()
+        if cache.found():
+            return cache
+        return BinaryTable.detect_buildcache()
 
     @classmethod
     def parse_entry(cls, entry: T.Union[str, T.List[str]]) -> T.Tuple[T.List[str], T.Union[None, ExternalProgram]]:
@@ -517,6 +524,9 @@ class BinaryTable:
         elif parts[0] == 'kache':
             compiler = parts[1:]
             ccache = cls.detect_kache()
+        elif parts[0] == 'buildcache':
+            compiler = parts[1:]
+            ccache = cls.detect_buildcache()
         else:
             compiler = parts
             ccache = None

unittests/allplatformstests.py

@@ -1341,7 +1341,7 @@ class AllPlatformTests(BasePlatformTests):
         for cmd in self.get_compdb():
             # Get compiler
             split = split_args(cmd['command'])
-            if os.path.basename(split[0]) in ('ccache', 'sccache'):
+            if os.path.basename(split[0]) in ('ccache', 'sccache', 'buildcache'):
                 compiler = split[1]
             else:
                 compiler = split[0]

unittests/failuretests.py

@@ -394,3 +394,12 @@ class FailureTests(BasePlatformTests):
         self.assertMesonRaises('',
                                'Compiler cache specified without compiler: ccache',
                                override_envvars={'CC': 'ccache'})
+        self.assertMesonRaises('',
+                               'Compiler cache specified without compiler: sccache',
+                               override_envvars={'CC': 'sccache'})
+        self.assertMesonRaises('',
+                               'Compiler cache specified without compiler: kache',
+                               override_envvars={'CC': 'kache'})
+        self.assertMesonRaises('',
+                               'Compiler cache specified without compiler: buildcache',
+                               override_envvars={'CC': 'buildcache'})