build: raise CompilerNotFoundError for null runtime

When the null runtime detects a missing compiler via is_supported(),
raise a specific CompilerNotFoundError instead of the generic
UnsupportedArchitectureToolchainCombination. This gives the user an
actionable error message naming the missing compiler and suggesting
to install it or use a container-based runtime.

Before:
  E: Unsupported architecture/toolchain combination: sparc64/gcc

After:
  E: Compiler not found: sparc64-linux-gnu-gcc
  Install the compiler or use a container-based runtime (e.g. --runtime=docker/podman)

Signed-off-by: Ben Copeland <ben.copeland@linaro.org>

Author: bhcopeland

test/test_build.py

@@ -889,10 +889,15 @@ def test_errors(self, build):
 
 class TestUnsupportedToolchainArchitectureCombination:
     def test_exception(self, linux, mocker):
-        mocker.patch("tuxmake.runtime.NullRuntime.is_supported", return_value=False)
+        mocker.patch("tuxmake.runtime.Runtime.is_supported", return_value=False)
         with pytest.raises(
             tuxmake.exceptions.UnsupportedArchitectureToolchainCombination
         ):
+            Build(tree=linux, target_arch="arc", toolchain="clang", runtime="docker")
+
+    def test_null_runtime_compiler_not_found(self, linux, mocker):
+        mocker.patch("tuxmake.runtime.NullRuntime.is_supported", return_value=False)
+        with pytest.raises(tuxmake.exceptions.CompilerNotFoundError):
             Build(tree=linux, target_arch="arc", toolchain="clang")
 
 

tuxmake/build.py

@@ -22,6 +22,7 @@
 from tuxmake.runtime import Runtime, DockerRuntime
 from tuxmake.runtime import Terminated
 from tuxmake.metadata import MetadataCollector
+from tuxmake.exceptions import CompilerNotFoundError
 from tuxmake.exceptions import DecodeStacktraceMissingVariable
 from tuxmake.exceptions import EnvironmentCheckFailed
 from tuxmake.exceptions import KorgGccPreparationFailed
@@ -246,6 +247,9 @@ def __init__(
         self.runtime.set_image(get_image(self))
 
         if not self.runtime.is_supported(self.target_arch, self.toolchain):
+            if self.runtime.name == "null":
+                compiler = self.toolchain.compiler(self.target_arch)
+                raise CompilerNotFoundError(compiler)
             raise UnsupportedArchitectureToolchainCombination(
                 f"{self.target_arch}/{self.toolchain}"
             )

tuxmake/exceptions.py

@@ -115,5 +115,12 @@ class KorgGccDownloadAllToolchainFailed(TuxMakeUserError):
     msg = "Korg GCC download all toochains failed"
 
 
+class CompilerNotFoundError(TuxMakeUserError):
+    msg = (
+        "Compiler not found: {name}\n"
+        "Install the compiler or use a container-based runtime (e.g. --runtime=docker/podman)"
+    )
+
+
 class DecodeStacktraceMissingVariable(TuxMakeUserError):
     msg = "Missing environment variable: {name}"