Bug 1319156 - part 1 - add features to RustLibrary objects and moz.build definitions; r=chmanchester

Ideally, people will just use the extra argument to RustLibrary to
define features for their library.

build/templates.mozbuild

@@ -61,11 +61,15 @@ def Library(name):
 
 
 @template
-def RustLibrary(name):
+def RustLibrary(name, features=None):
     '''Template for Rust libraries.'''
     Library(name)
 
+    if not features:
+        features = []
+
     IS_RUST_LIBRARY = True
+    RUST_LIBRARY_FEATURES = features
 
 
 @template

python/mozbuild/mozbuild/frontend/context.py

@@ -952,6 +952,13 @@ VARIABLES = {
         a Cargo.toml file that exists in this moz.build's directory.
         """),
 
+    'RUST_LIBRARY_FEATURES': (List, list,
+        """Cargo features to activate for this library.
+
+        This variable should not be used directly; you should be using the
+        RustLibrary template instead.
+        """),
+
     'UNIFIED_SOURCES': (ContextDerivedTypedList(SourcePath, StrictOrderingOnAppendList), list,
         """Source code files that can be compiled together.
 

python/mozbuild/mozbuild/frontend/data.py

@@ -526,9 +526,11 @@ class RustLibrary(StaticLibrary):
         'crate_type',
         'dependencies',
         'deps_path',
+        'features',
     )
 
-    def __init__(self, context, basename, cargo_file, crate_type, dependencies, **args):
+    def __init__(self, context, basename, cargo_file, crate_type, dependencies,
+                 features, **args):
         StaticLibrary.__init__(self, context, basename, **args)
         self.cargo_file = cargo_file
         self.crate_type = crate_type
@@ -544,6 +546,7 @@ class RustLibrary(StaticLibrary):
         build_dir = cargo_target_directory(context)
         self.import_name = mozpath.join(build_dir, self.lib_name)
         self.deps_path = mozpath.join(build_dir, 'deps')
+        self.features = features
 
 
 class SharedLibrary(Library):

python/mozbuild/mozbuild/frontend/emitter.py

@@ -513,8 +513,15 @@ class TreeMetadataEmitter(LoggingMixin):
 
         dependencies = set(config.get('dependencies', {}).iterkeys())
 
+        features = context.get('RUST_LIBRARY_FEATURES', [])
+        unique_features = set(features)
+        if len(features) != len(unique_features):
+            raise SandboxValidationError(
+                'features for %s should not contain duplicates: %s' % (libname, features),
+                context)
+
         return RustLibrary(context, libname, cargo_file, crate_type,
-                           dependencies, **static_args)
+                           dependencies, features, **static_args)
 
     def _handle_linkables(self, context, passthru, generated_files):
         linkables = []