Bug 1546136 - dump cmake logs on command failures; r=firefox-build-system-reviewers,chmanchester

CMake errors can be pretty opaque, especially if CMake is being run
inside the Ninja build process.  Let's try to surface those errors to
make problems easier to debug.

Differential Revision: https://phabricator.services.mozilla.com/D28360

build/build-clang/build-clang.py

@@ -32,7 +32,27 @@ def symlink(source, link_name):
 
 def check_run(args):
     print >> sys.stderr, ' '.join(args)
-    r = subprocess.call(args)
+    p = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    # CMake `message(STATUS)` messages, as appearing in failed source code
+    # compiles, appear on stdout, so we only capture that.
+    (out, _) = p.communicate()
+    r = p.returncode
+    if r != 0:
+        cmake_output_re = re.compile("See also \"(.*/CMakeOutput.log)\"")
+        cmake_error_re = re.compile("See also \"(.*/CMakeError.log)\"")
+        output_match = cmake_output_re.search(out)
+        error_match = cmake_error_re.search(out)
+
+        print >> sys.stderr, out
+
+        def dump_file(log):
+            with open(log, 'rb') as f:
+                print >> sys.stderr, "\nContents of", log, "follow\n"
+                print >> sys.stderr, f.read()
+        if output_match:
+            dump_file(output_match.group(1))
+        if error_match:
+            dump_file(error_match.group(1))
     assert r == 0