rust: add to_system_dependency

Move the logic for system dependencies outside Cargo.interpreter and
into the rust module, so that it can be reused by the workspace object.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

4 files changed, 44 insertions, 4 deletions

diff --git a/docs/markdown/Rust-module.md b/docs/markdown/Rust-module.md
index b1edb793c..37ba59d8e 100644
--- a/docs/markdown/Rust-module.md
+++ b/docs/markdown/Rust-module.md
@@ -172,6 +172,21 @@ Only a subset of [[shared_library]] keyword arguments are allowed:
 - link_with
 - override_options
 
+### to_system_dependency()
+
+*Since 1.11.0*
+
+```meson
+rustmod.to_system_dependency(dep[, name])
+```
+
+Create and return an internal dependency that wraps `dep` and
+defines `cfg(system_deps_have_NAME)`.  This is compatible with
+how the `system-deps` crate reports the availability of a system
+dependency to Rust code.
+
+If omitted, the name defaults to the name of the dependency.
+
 ### workspace()
 
 Basic usage:
diff --git a/mesonbuild/build.py b/mesonbuild/build.py
index f46bd616f..2ae47a858 100644
--- a/mesonbuild/build.py
+++ b/mesonbuild/build.py
@@ -1437,10 +1437,10 @@ class BuildTarget(Target):
                 self.link_whole_targets.extend(dep.whole_libraries)
                 if dep.get_compile_args() or dep.get_link_args():
                     # Those parts that are external.
-                    extpart = dependencies.InternalDependency(dep.version,
-                                                              compile_args=dep.get_compile_args(),
-                                                              link_args=dep.get_link_args(),
-                                                              name=dep.name)
+                    extpart = type(dep)(dep.version,
+                                        compile_args=dep.get_compile_args(),
+                                        link_args=dep.get_link_args(),
+                                        name=dep.name)
                     self.external_deps.append(extpart)
                 # Deps of deps.
                 self.add_deps(dep.ext_deps)
diff --git a/mesonbuild/compilers/rust.py b/mesonbuild/compilers/rust.py
index ab0706d26..7ad7f34e9 100644
--- a/mesonbuild/compilers/rust.py
+++ b/mesonbuild/compilers/rust.py
@@ -11,6 +11,7 @@ import re
 import typing as T
 
 from .. import options
+from ..dependencies import InternalDependency
 from ..mesonlib import EnvironmentException, MesonException, Popen_safe_logged, version_compare
 from ..linkers.linkers import VisualStudioLikeLinkerMixin
 from ..options import OptionKey
@@ -73,6 +74,11 @@ def rustc_link_args(args: T.List[str]) -> T.List[str]:
         rustc_args.append(f'link-arg={arg}')
     return rustc_args
 
+
+class RustSystemDependency(InternalDependency):
+    pass
+
+
 class RustCompiler(Compiler):
 
     # rustc doesn't invoke the compiler itself, it doesn't need a LINKER_PREFIX
@@ -323,6 +329,8 @@ class RustCompiler(Compiler):
         return opts
 
     def get_dependency_compile_args(self, dep: 'Dependency') -> T.List[str]:
+        if isinstance(dep, RustSystemDependency):
+            return dep.get_compile_args()
         # Rust doesn't have dependency compile arguments so simply return
         # nothing here. Dependencies are linked and all required metadata is
         # provided by the linker flags.
diff --git a/mesonbuild/modules/rust.py b/mesonbuild/modules/rust.py
index 0ea1c8f7e..5ba2a5f17 100644
--- a/mesonbuild/modules/rust.py
+++ b/mesonbuild/modules/rust.py
@@ -15,6 +15,7 @@ from .. import mesonlib, mlog
 from ..build import (BothLibraries, BuildTarget, CustomTargetIndex, Executable, ExtractedObjects, GeneratedList,
                      CustomTarget, InvalidArguments, Jar, StructuredSources, SharedLibrary, StaticLibrary)
 from ..compilers.compilers import are_asserts_disabled_for_subproject, lang_suffixes
+from ..compilers.rust import RustSystemDependency
 from ..dependencies import Dependency
 from ..interpreter.type_checking import (
     DEPENDENCIES_KW, LINK_WITH_KW, LINK_WHOLE_KW, SHARED_LIB_KWS, TEST_KWS, TEST_KWS_NO_ARGS,
@@ -259,6 +260,7 @@ class RustModule(ExtensionModule):
             'doctest': self.doctest,
             'bindgen': self.bindgen,
             'proc_macro': self.proc_macro,
+            'to_system_dependency': self.to_system_dependency,
             'workspace': self.workspace,
         })
 
@@ -657,6 +659,21 @@ class RustModule(ExtensionModule):
         target = state._interpreter.build_target(state.current_node, args, kwargs, SharedLibrary)
         return target
 
+    @FeatureNew('rust.to_system_dependency', '1.11.0')
+    @typed_pos_args('rust.to_system_dependency', Dependency, optargs=[str])
+    @noKwargs
+    def to_system_dependency(self, state: ModuleState, args: T.Tuple[Dependency, T.Optional[str]], kwargs: TYPE_kwargs) -> Dependency:
+        dep, depname = args
+        if not dep.found():
+            return dep
+        if not depname:
+            if not dep.name:
+                raise MesonException("rust.to_system_dependency() called with an unnamed dependency and no explicit name")
+            depname = dep.name
+        depname = re.sub(r'[^a-zA-Z0-9]', '_', depname)
+        rust_args = ['--cfg', f'system_deps_have_{depname}']
+        return RustSystemDependency(dep.version, compile_args=rust_args, ext_deps=[dep], name=dep.name)
+
     @FeatureNew('rust.workspace', '1.11.0')
     @noPosargs
     @typed_kwargs(