compiler: allow non-built internal dependencies as arguments

Allow methods on the compiler object to receive internal dependencies,
as long as they only specify compiler/linker arguments or other
dependencies that satisfy the same requirements.

This is useful if you're using internal dependencies to add special
"-D" flags such as -DNCURSES_WIDECHAR, -D_XOPEN_SOURCE_EXTENDED or
-DGLIB_STATIC_COMPILATION.

4 files changed, 35 insertions, 13 deletions

diff --git a/docs/markdown/snippets/compiler_method_internal_deps.md b/docs/markdown/snippets/compiler_method_internal_deps.md
new file mode 100644
index 0000000..bde6b4f
--- /dev/null
+++ b/docs/markdown/snippets/compiler_method_internal_deps.md
@@ -0,0 +1,6 @@
+## Passing internal dependencies to the compiler object
+
+Methods on the compiler object (such as `compiles`, `links`, `has_header`)
+can be passed dependencies returned by `declare_dependency`, as long as they
+only specify compiler/linker arguments or other dependencies that satisfy
+the same requirements.
diff --git a/mesonbuild/dependencies/base.py b/mesonbuild/dependencies/base.py
index ebe5b62..9026876 100644
--- a/mesonbuild/dependencies/base.py
+++ b/mesonbuild/dependencies/base.py
@@ -33,7 +33,7 @@ from .. import mlog
 from .. import mesonlib
 from ..compilers import clib_langs
 from ..envconfig import get_env_var
-from ..environment import BinaryTable, Environment, MachineInfo
+from ..environment import Environment, MachineInfo
 from ..cmake import CMakeExecutor, CMakeTraceParser, CMakeException, CMakeToolchain, CMakeExecScope, check_cmake_args
 from ..mesonlib import MachineChoice, MesonException, OrderedSet, PerMachine
 from ..mesonlib import Popen_safe, version_compare_many, version_compare, listify, stringlistify, extract_as_list, split_args
@@ -84,7 +84,7 @@ def find_external_program(env: Environment, for_machine: MachineChoice, name: st
     potential_path = env.lookup_binary_entry(for_machine, name)
     if potential_path is not None:
         mlog.debug('{} binary for {} specified from cross file, native file, '
-                    'or env var as {}'.format(display_name, for_machine, potential_path))
+                   'or env var as {}'.format(display_name, for_machine, potential_path))
         yield ExternalProgram.from_entry(name, potential_path)
         # We never fallback if the user-specified option is no good, so
         # stop returning options.
@@ -132,6 +132,9 @@ class Dependency:
         s = '<{0} {1}: {2}>'
         return s.format(self.__class__.__name__, self.name, self.is_found)
 
+    def is_built(self) -> bool:
+        return False
+
     def get_compile_args(self) -> T.List[str]:
         if self.include_type == 'system':
             converted = []
@@ -261,6 +264,11 @@ class InternalDependency(Dependency):
                 setattr(result, k, copy.deepcopy(v, memo))
         return result
 
+    def is_built(self) -> bool:
+        if self.sources or self.libraries or self.whole_libraries:
+            return True
+        return any(d.is_built() for d in self.ext_deps)
+
     def get_pkgconfig_variable(self, variable_name: str, kwargs: T.Dict[str, T.Any]) -> str:
         raise DependencyException('Method "get_pkgconfig_variable()" is '
                                   'invalid for an internal dependency')
@@ -665,7 +673,6 @@ class PkgConfigDependency(ExternalDependency):
             env['PKG_CONFIG_LIBDIR'] = new_pkg_config_libdir
             mlog.debug('PKG_CONFIG_LIBDIR: ' + new_pkg_config_libdir)
 
-
     def _call_pkgbin(self, args, env=None):
         # Always copy the environment since we're going to modify it
         # with pkg-config variables
diff --git a/mesonbuild/interpreter.py b/mesonbuild/interpreter.py
index 5337984..83acc01 100644
--- a/mesonbuild/interpreter.py
+++ b/mesonbuild/interpreter.py
@@ -1120,14 +1120,18 @@ class CompilerHolder(InterpreterObject):
             return endl
         if endl is None:
             endl = ''
-        tpl = msg_many if len(deps) > 1 else msg_single
         names = []
         for d in deps:
+            if isinstance(d, dependencies.InternalDependency):
+                continue
             if isinstance(d, dependencies.ExternalLibrary):
                 name = '-l' + d.name
             else:
                 name = d.name
             names.append(name)
+        if not names:
+            return None
+        tpl = msg_many if len(names) > 1 else msg_single
         return tpl.format(', '.join(names)) + endl
 
     @noPosargs
@@ -1165,16 +1169,15 @@ class CompilerHolder(InterpreterObject):
     def determine_dependencies(self, kwargs, endl=':'):
         deps = kwargs.get('dependencies', None)
         if deps is not None:
-            deps = listify(deps)
             final_deps = []
-            for d in deps:
-                try:
-                    d = d.held_object
-                except Exception:
-                    pass
-                if isinstance(d, InternalDependency) or not isinstance(d, Dependency):
-                    raise InterpreterException('Dependencies must be external dependencies')
-                final_deps.append(d)
+            while deps:
+                next_deps = []
+                for d in unholder(listify(deps)):
+                    if not isinstance(d, Dependency) or d.is_built():
+                        raise InterpreterException('Dependencies must be external dependencies')
+                    final_deps.append(d)
+                    next_deps.extend(d.ext_deps)
+                deps = next_deps
             deps = final_deps
         return deps, self._dep_msg(deps, endl)
 
diff --git a/test cases/linuxlike/2 external library/meson.build b/test cases/linuxlike/2 external library/meson.build
index fbe661a..3188ebf 100644
--- a/test cases/linuxlike/2 external library/meson.build
+++ b/test cases/linuxlike/2 external library/meson.build
@@ -18,6 +18,12 @@ int main(void) {
 '''
 
 assert(cc.links(linkcode, args : '-lz', name : 'Test link against zlib'), 'Linking test failed.')
+d1 = declare_dependency(compile_args: '-DSOMETHING', link_args: '-lz')
+assert(cc.links(linkcode, dependencies : d1,
+                name : 'Test link against zlib via declare_dependency'), 'Linking test failed.')
+d2 = declare_dependency(dependencies: d1)
+assert(cc.links(linkcode, dependencies : d2,
+                name : 'Test link against zlib via indirect declare_dependency'), 'Linking test failed.')
 assert(not cc.links(nolinkcode, name : 'Failing link'), 'Linking succeeded when it should have failed.')
 
 e = executable('zprog', 'prog.c', dependencies : zlib)