Skip collection of compilers which report an empty version (#6684)

Fixes #6200

For compilers that successfully run a version detection script but
don't actually return a version, Spack was keeping track of the
empty version and then failing when attempting to construct a
compiler spec. This skips any attempt to add a compiler entry when
no version is reported (but logs when a compiler fails to report
a version).

lib/spack/spack/compiler.py

@@ -278,27 +278,11 @@ def _find_matches_in_path(cls, compiler_names, detect_version, *path):
 
                     match = re.match(regex, exe)
                     if match:
-                        key = (full_path,) + match.groups()
+                        key = (full_path,) + match.groups() + (detect_version,)
                         checks.append(key)
 
-        def check(key):
-            try:
-                full_path, prefix, suffix = key
-                version = detect_version(full_path)
-                return (version, prefix, suffix, full_path)
-            except ProcessError as e:
-                tty.debug(
-                    "Couldn't get version for compiler %s" % full_path, e)
-                return None
-            except Exception as e:
-                # Catching "Exception" here is fine because it just
-                # means something went wrong running a candidate executable.
-                tty.debug("Error while executing candidate compiler %s"
-                          % full_path,
-                          "%s: %s" % (e.__class__.__name__, e))
-                return None
-
-        successful = [k for k in parmap(check, checks) if k is not None]
+        successful = [k for k in parmap(_get_versioned_tuple, checks)
+                      if k is not None]
 
         # The 'successful' list is ordered like the input paths.
         # Reverse it here so that the dict creation (last insert wins)
@@ -322,6 +306,28 @@ def __str__(self):
                 str(self.operating_system)))))
 
 
+def _get_versioned_tuple(compiler_check_tuple):
+    full_path, prefix, suffix, detect_version = compiler_check_tuple
+    try:
+        version = detect_version(full_path)
+        if (not version) or (not str(version).strip()):
+            tty.debug(
+                "Couldn't get version for compiler %s" % full_path)
+            return None
+        return (version, prefix, suffix, full_path)
+    except ProcessError as e:
+        tty.debug(
+            "Couldn't get version for compiler %s" % full_path, e)
+        return None
+    except Exception as e:
+        # Catching "Exception" here is fine because it just
+        # means something went wrong running a candidate executable.
+        tty.debug("Error while executing candidate compiler %s"
+                  % full_path,
+                  "%s: %s" % (e.__class__.__name__, e))
+        return None
+
+
 class CompilerAccessError(spack.error.SpackError):
 
     def __init__(self, path):

lib/spack/spack/test/compilers.py

@@ -27,6 +27,7 @@
 
 import spack.spec
 import spack.compilers as compilers
+from spack.compiler import _get_versioned_tuple
 
 
 @pytest.mark.usefixtures('config')
@@ -49,6 +50,19 @@ def test_all_compilers(self):
         assert len(filtered) == 1
 
 
+def test_version_detection_is_empty():
+    no_version = lambda x: None
+    compiler_check_tuple = ('/usr/bin/gcc', '', r'\d\d', no_version)
+    assert not _get_versioned_tuple(compiler_check_tuple)
+
+
+def test_version_detection_is_successful():
+    version = lambda x: '4.9'
+    compiler_check_tuple = ('/usr/bin/gcc', '', r'\d\d', version)
+    assert _get_versioned_tuple(compiler_check_tuple) == (
+        '4.9', '', r'\d\d', '/usr/bin/gcc')
+
+
 def test_compiler_flags_from_config_are_grouped():
     compiler_entry = {
         'spec': 'intel@17.0.2',