bugfix: ignore Apple's "gcc" by default (#17589)

Apple's gcc is really clang. We previously ignored it by default but
there was a regression in #17110.

Originally we checked for all clang versions with this, but I know of
none other than `gcc` on macos that actually do this, so limiting to
`apple-clang` should be ok.

- [x] Fix check for `apple-clang` in `gcc.py` to use version detection
  from `spack.compilers.apple_clang`

3 files changed, 51 insertions, 29 deletions

diff --git a/lib/spack/spack/compilers/apple_clang.py b/lib/spack/spack/compilers/apple_clang.py
index 8ef58550ea..63e0a9c42f 100644
--- a/lib/spack/spack/compilers/apple_clang.py
+++ b/lib/spack/spack/compilers/apple_clang.py
@@ -23,7 +23,12 @@ class AppleClang(spack.compilers.clang.Clang):
         ver = 'unknown'
         match = re.search(
             # Apple's LLVM compiler has its own versions, so suffix them.
-            r'^Apple (?:LLVM|clang) version ([^ )]+)', output
+            r'^Apple (?:LLVM|clang) version ([^ )]+)',
+            output,
+            # Multi-line, since 'Apple clang' may not be on the first line
+            # in particular, when run as gcc, it seems to output
+            # "Configured with: --prefix=..." as the first line
+            re.M,
         )
         if match:
             ver = match.group(match.lastindex)
diff --git a/lib/spack/spack/compilers/gcc.py b/lib/spack/spack/compilers/gcc.py
index 98809eea25..8a19e7d1b5 100644
--- a/lib/spack/spack/compilers/gcc.py
+++ b/lib/spack/spack/compilers/gcc.py
@@ -5,13 +5,13 @@
 
 import re
 
-import spack.compilers.clang
+import spack.compiler
+import spack.compilers.apple_clang as apple_clang
 
-from spack.compiler import Compiler, UnsupportedCompilerFlag
 from spack.version import ver
 
 
-class Gcc(Compiler):
+class Gcc(spack.compiler.Compiler):
     # Subclasses use possible names of C compiler
     cc_names = ['gcc']
 
@@ -64,10 +64,8 @@ class Gcc(Compiler):
     @property
     def cxx11_flag(self):
         if self.version < ver('4.3'):
-            raise UnsupportedCompilerFlag(self,
-                                          "the C++11 standard",
-                                          "cxx11_flag",
-                                          " < 4.3")
+            raise spack.compiler.UnsupportedCompilerFlag(
+                self, "the C++11 standard", "cxx11_flag", " < 4.3")
         elif self.version < ver('4.7'):
             return "-std=c++0x"
         else:
@@ -76,10 +74,8 @@ class Gcc(Compiler):
     @property
     def cxx14_flag(self):
         if self.version < ver('4.8'):
-            raise UnsupportedCompilerFlag(self,
-                                          "the C++14 standard",
-                                          "cxx14_flag",
-                                          "< 4.8")
+            raise spack.compiler.UnsupportedCompilerFlag(
+                self, "the C++14 standard", "cxx14_flag", "< 4.8")
         elif self.version < ver('4.9'):
             return "-std=c++1y"
         elif self.version < ver('6.0'):
@@ -90,10 +86,8 @@ class Gcc(Compiler):
     @property
     def cxx17_flag(self):
         if self.version < ver('5.0'):
-            raise UnsupportedCompilerFlag(self,
-                                          "the C++17 standard",
-                                          "cxx17_flag",
-                                          "< 5.0")
+            raise spack.compiler.UnsupportedCompilerFlag(
+                self, "the C++17 standard", "cxx17_flag", "< 5.0")
         elif self.version < ver('6.0'):
             return "-std=c++1z"
         else:
@@ -102,19 +96,15 @@ class Gcc(Compiler):
     @property
     def c99_flag(self):
         if self.version < ver('4.5'):
-            raise UnsupportedCompilerFlag(self,
-                                          "the C99 standard",
-                                          "c99_flag",
-                                          "< 4.5")
+            raise spack.compiler.UnsupportedCompilerFlag(
+                self, "the C99 standard", "c99_flag", "< 4.5")
         return "-std=c99"
 
     @property
     def c11_flag(self):
         if self.version < ver('4.7'):
-            raise UnsupportedCompilerFlag(self,
-                                          "the C11 standard",
-                                          "c11_flag",
-                                          "< 4.7")
+            raise spack.compiler.UnsupportedCompilerFlag(
+                self, "the C11 standard", "c11_flag", "< 4.7")
         return "-std=c11"
 
     @property
@@ -152,10 +142,10 @@ class Gcc(Compiler):
 
             7.2.0
         """
-        # Skip any gcc versions that are actually clang, like Apple's gcc.
-        # Returning "unknown" makes them not detected by default.
-        # Users can add these manually to compilers.yaml at their own risk.
-        if spack.compilers.clang.Clang.default_version(cc) != 'unknown':
+        # Apple's gcc is actually apple clang, so skip it. Returning
+        # "unknown" ensures this compiler is not detected by default.
+        # Users can add it manually to compilers.yaml at their own risk.
+        if apple_clang.AppleClang.default_version(cc) != 'unknown':
             return 'unknown'
 
         version = super(Gcc, cls).default_version(cc)
diff --git a/lib/spack/spack/test/cmd/compiler.py b/lib/spack/spack/test/cmd/compiler.py
index 0476275a5f..f496727081 100644
--- a/lib/spack/spack/test/cmd/compiler.py
+++ b/lib/spack/spack/test/cmd/compiler.py
@@ -64,7 +64,7 @@ def test_compiler_find_without_paths(no_compilers_yaml, working_env, tmpdir):
     with tmpdir.as_cwd():
         with open('gcc', 'w') as f:
             f.write("""\
-#!/bin/bash
+#!/bin/sh
 echo "0.0.0"
 """)
         os.chmod('gcc', 0o700)
@@ -75,6 +75,33 @@ echo "0.0.0"
     assert 'gcc' in output
 
 
+@pytest.mark.regression('17589')
+def test_compiler_find_no_apple_gcc(no_compilers_yaml, working_env, tmpdir):
+    with tmpdir.as_cwd():
+        # make a script to emulate apple gcc's version args
+        with open('gcc', 'w') as f:
+            f.write("""\
+#!/bin/sh
+if [ "$1" = "-dumpversion" ]; then
+    echo "4.2.1"
+elif [ "$1" = "--version" ]; then
+    echo "Configured with: --prefix=/dummy"
+    echo "Apple clang version 11.0.0 (clang-1100.0.33.16)"
+    echo "Target: x86_64-apple-darwin18.7.0"
+    echo "Thread model: posix"
+    echo "InstalledDir: /dummy"
+else
+    echo "clang: error: no input files"
+fi
+""")
+        os.chmod('gcc', 0o700)
+
+    os.environ['PATH'] = str(tmpdir)
+    output = compiler('find', '--scope=site')
+
+    assert 'gcc' not in output
+
+
 def test_compiler_remove(mutable_config, mock_packages):
     args = spack.util.pattern.Bunch(
         all=True, compiler_spec='gcc@4.5.0', add_paths=[], scope=None