Fix crash when toolchain is missing

Add a MissingCompiler class returned by compiler detecting methods
intead of None - accessing such an object raises a DependencyException

Fixes #10586

Co-authored-by: duckflyer <duckflyer@gmail.com>

7 files changed, 23 insertions, 13 deletions

diff --git a/mesonbuild/dependencies/__init__.py b/mesonbuild/dependencies/__init__.py
index bbf31ad..b6fdb18 100644
--- a/mesonbuild/dependencies/__init__.py
+++ b/mesonbuild/dependencies/__init__.py
@@ -15,7 +15,7 @@
 from .boost import BoostDependency
 from .cuda import CudaDependency
 from .hdf5 import hdf5_factory
-from .base import Dependency, InternalDependency, ExternalDependency, NotFoundDependency
+from .base import Dependency, InternalDependency, ExternalDependency, NotFoundDependency, MissingCompiler
 from .base import (
         ExternalLibrary, DependencyException, DependencyMethods,
         BuiltinDependency, SystemDependency, get_leaf_external_dependencies)
@@ -52,6 +52,7 @@ __all__ = [
     'ExternalLibrary',
     'DependencyException',
     'DependencyMethods',
+    'MissingCompiler',
 
     'CMakeDependency',
     'ConfigToolDependency',
diff --git a/mesonbuild/dependencies/base.py b/mesonbuild/dependencies/base.py
index d901ef9..e78a420 100644
--- a/mesonbuild/dependencies/base.py
+++ b/mesonbuild/dependencies/base.py
@@ -46,6 +46,19 @@ class DependencyException(MesonException):
     '''Exceptions raised while trying to find dependencies'''
 
 
+class MissingCompiler:
+    """Represent a None Compiler - when no tool chain is found.
+    replacing AttributeError with DependencyException"""
+
+    def __getattr__(self, item: str) -> T.Any:
+        if item.startswith('__'):
+            raise AttributeError()
+        raise DependencyException('no toolchain found')
+
+    def __bool__(self) -> bool:
+        return False
+
+
 class DependencyMethods(Enum):
     # Auto means to use whatever dependency checking mechanisms in whatever order meson thinks is best.
     AUTO = 'auto'
@@ -361,7 +374,7 @@ class ExternalDependency(Dependency, HasNativeKwarg):
         HasNativeKwarg.__init__(self, kwargs)
         self.clib_compiler = detect_compiler(self.name, environment, self.for_machine, self.language)
 
-    def get_compiler(self) -> 'Compiler':
+    def get_compiler(self) -> T.Union['MissingCompiler', 'Compiler']:
         return self.clib_compiler
 
     def get_partial_dependency(self, *, compile_args: bool = False,
@@ -573,7 +586,7 @@ def process_method_kw(possible: T.Iterable[DependencyMethods], kwargs: T.Dict[st
     return methods
 
 def detect_compiler(name: str, env: 'Environment', for_machine: MachineChoice,
-                    language: T.Optional[str]) -> T.Optional['Compiler']:
+                    language: T.Optional[str]) -> T.Union['MissingCompiler', 'Compiler']:
     """Given a language and environment find the compiler used."""
     compilers = env.coredata.compilers[for_machine]
 
@@ -591,7 +604,7 @@ def detect_compiler(name: str, env: 'Environment', for_machine: MachineChoice,
                 return compilers[lang]
             except KeyError:
                 continue
-    return None
+    return MissingCompiler()
 
 
 class SystemDependency(ExternalDependency):
diff --git a/mesonbuild/dependencies/cuda.py b/mesonbuild/dependencies/cuda.py
index d9b69c5..608d4f7 100644
--- a/mesonbuild/dependencies/cuda.py
+++ b/mesonbuild/dependencies/cuda.py
@@ -283,7 +283,7 @@ class CudaDependency(SystemDependency):
         return candidates
 
     def get_link_args(self, language: T.Optional[str] = None, raw: bool = False) -> T.List[str]:
-        args = []
+        args: T.List[str] = []
         if self.libdir:
             args += self.clib_compiler.get_linker_search_args(self.libdir)
         for lib in self.requested_modules:
diff --git a/mesonbuild/dependencies/dev.py b/mesonbuild/dependencies/dev.py
index 606bb4f..b345387 100644
--- a/mesonbuild/dependencies/dev.py
+++ b/mesonbuild/dependencies/dev.py
@@ -499,11 +499,6 @@ class ZlibSystemDependency(SystemDependency):
             self.is_found = True
             self.link_args = ['-lz']
         else:
-            # Without a clib_compiler we can't find zlib, so just give up.
-            if self.clib_compiler is None:
-                self.is_found = False
-                return
-
             if self.clib_compiler.get_argument_syntax() == 'msvc':
                 libs = ['zlib1' 'zlib']
             else:
diff --git a/mesonbuild/dependencies/misc.py b/mesonbuild/dependencies/misc.py
index a5b1f41..e5f92b3 100644
--- a/mesonbuild/dependencies/misc.py
+++ b/mesonbuild/dependencies/misc.py
@@ -145,7 +145,7 @@ class ThreadDependency(SystemDependency):
         self.is_found = True
         # Happens if you are using a language with threads
         # concept without C, such as plain Cuda.
-        if self.clib_compiler is None:
+        if not self.clib_compiler:
             self.compile_args = []
             self.link_args = []
         else:
diff --git a/mesonbuild/dependencies/mpi.py b/mesonbuild/dependencies/mpi.py
index 2354767..a99a4cc 100644
--- a/mesonbuild/dependencies/mpi.py
+++ b/mesonbuild/dependencies/mpi.py
@@ -40,7 +40,7 @@ def mpi_factory(env: 'Environment',
 
     candidates: T.List['DependencyGenerator'] = []
     compiler = detect_compiler('mpi', env, for_machine, language)
-    if compiler is None:
+    if not compiler:
         return []
     compiler_is_intel = compiler.get_id() in {'intel', 'intel-cl'}
 
diff --git a/mesonbuild/dependencies/qt.py b/mesonbuild/dependencies/qt.py
index e1e9e07..c6162ed 100644
--- a/mesonbuild/dependencies/qt.py
+++ b/mesonbuild/dependencies/qt.py
@@ -33,6 +33,7 @@ if T.TYPE_CHECKING:
     from ..compilers import Compiler
     from ..envconfig import MachineInfo
     from ..environment import Environment
+    from ..dependencies import MissingCompiler
 
 
 def _qt_get_private_includes(mod_inc_dir: str, module: str, mod_version: str) -> T.List[str]:
@@ -122,7 +123,7 @@ class _QtBase:
     """Mixin class for shared components between PkgConfig and Qmake."""
 
     link_args: T.List[str]
-    clib_compiler: 'Compiler'
+    clib_compiler: T.Union['MissingCompiler', 'Compiler']
     env: 'Environment'
     libexecdir: T.Optional[str] = None