dependencies: allow get_variable to expose files from subprojects

There are somewhat common, reasonable and legitimate use cases for a
dependency to provide data files installed to /usr which are used as
command inputs. When getting a dependency from a subproject, however,
the attempt to directly construct an input file from a subproject
results in a sandbox violation. This means not all dependencies can be
wrapped as a subproject.

One example is wayland-protocols XML files which get scanned and used to
produce C source files.

Teach Meson to recognize when a string path is the result of fetching a
dep.get_variable(), and special case this to be exempt from subproject
violations.

A requirement of this is that the file must be installed by
install_data() or install_subdir() because otherwise it is not actually
representative of what a pkg-config dependency would provide.

1 files changed, 3 insertions, 2 deletions

diff --git a/mesonbuild/interpreter/interpreterobjects.py b/mesonbuild/interpreter/interpreterobjects.py
index 39085e5..4aa5548 100644
--- a/mesonbuild/interpreter/interpreterobjects.py
+++ b/mesonbuild/interpreter/interpreterobjects.py
@@ -21,6 +21,7 @@ from ..interpreterbase import (
                                typed_pos_args, typed_kwargs, typed_operator,
                                noArgsFlattening, noPosargs, noKwargs, unholder_return,
                                flatten, resolve_second_level_holders, InterpreterException, InvalidArguments, InvalidCode)
+from ..interpreter.primitives import DependencyVariableString
 from ..interpreter.type_checking import NoneType, ENV_SEPARATOR_KW
 from ..dependencies import Dependency, ExternalLibrary, InternalDependency
 from ..programs import ExternalProgram
@@ -483,14 +484,14 @@ class DependencyHolder(ObjectHolder[Dependency]):
         default_varname = args[0]
         if default_varname is not None:
             FeatureNew('Positional argument to dependency.get_variable()', '0.58.0').use(self.subproject, self.current_node)
-        return self.held_object.get_variable(
+        return DependencyVariableString(self.held_object.get_variable(
             cmake=kwargs['cmake'] or default_varname,
             pkgconfig=kwargs['pkgconfig'] or default_varname,
             configtool=kwargs['configtool'] or default_varname,
             internal=kwargs['internal'] or default_varname,
             default_value=kwargs['default_value'],
             pkgconfig_define=kwargs['pkgconfig_define'],
-        )
+        ))
 
     @FeatureNew('dependency.include_type', '0.52.0')
     @noPosargs