Bugfix/install missing compiler from buildcache (#17536)

Ensure compilers installed from buildcache are registered.

lib/spack/spack/installer.py

@@ -1057,6 +1057,9 @@ def _install_task(self, task, **kwargs):
         if use_cache and \
                 _install_from_cache(pkg, cache_only, explicit, unsigned):
             self._update_installed(task)
+            if task.compiler:
+                spack.compilers.add_compilers_to_config(
+                    spack.compilers.find_compilers([pkg.spec.prefix]))
             return
 
         pkg.run_tests = (tests is True or tests and pkg.name in tests)

lib/spack/spack/test/cmd/install.py

@@ -29,6 +29,9 @@
 install = SpackCommand('install')
 env = SpackCommand('env')
 add = SpackCommand('add')
+mirror = SpackCommand('mirror')
+uninstall = SpackCommand('uninstall')
+buildcache = SpackCommand('buildcache')
 
 
 @pytest.fixture()
@@ -733,6 +736,40 @@ def test_compiler_bootstrap(
     install('a%gcc@2.0')
 
 
+def test_compiler_bootstrap_from_binary_mirror(
+        install_mockery_mutable_config, mock_packages, mock_fetch,
+        mock_archive, mutable_config, monkeypatch, tmpdir):
+    """Make sure installing compiler from buildcache registers compiler"""
+
+    # Create a temp mirror directory for buildcache usage
+    mirror_dir = tmpdir.join('mirror_dir')
+    mirror_url = 'file://{0}'.format(mirror_dir.strpath)
+
+    # Install a compiler, because we want to put it in a buildcache
+    install('gcc@2.0')
+
+    # Put installed compiler in the buildcache
+    buildcache('create', '-u', '-a', '-f', '-d', mirror_dir.strpath, 'gcc@2.0')
+
+    # Now uninstall the compiler
+    uninstall('-y', 'gcc@2.0')
+
+    monkeypatch.setattr(spack.concretize.Concretizer,
+                        'check_for_compiler_existence', False)
+    spack.config.set('config:install_missing_compilers', True)
+    assert CompilerSpec('gcc@2.0') not in compilers.all_compiler_specs()
+
+    # Configure the mirror where we put that buildcache w/ the compiler
+    mirror('add', 'test-mirror', mirror_url)
+
+    # Now make sure that when the compiler is installed from binary mirror,
+    # it also gets configured as a compiler.  Test succeeds if it does not
+    # raise an error
+    install('--no-check-signature', '--cache-only', '--only',
+            'dependencies', 'b%gcc@2.0')
+    install('--no-cache', '--only', 'package', 'b%gcc@2.0')
+
+
 @pytest.mark.regression('16221')
 def test_compiler_bootstrap_already_installed(
         install_mockery_mutable_config, mock_packages, mock_fetch,