Bug 1629789 - Suppress `fix-stacks` errors on web platform tests. r=erahm,jgraham

Because the web platform test harness doesn't recognize them and annotates them
with `CRITICAL`, which is disconcerting, even though those errors are typically
not harmful.

Differential Revision: https://phabricator.services.mozilla.com/D71485

testing/mozbase/mozrunner/mozrunner/utils.py

@@ -224,7 +224,7 @@ def test_environment(xrePath, env=None, crashreporter=True, debugger=False,
     return env
 
 
-def get_stack_fixer_function(utilityPath, symbolsPath):
+def get_stack_fixer_function(utilityPath, symbolsPath, hideErrors=False):
     """
     Return a stack fixing function, if possible, to use on output lines.
 
@@ -254,7 +254,7 @@ def get_stack_fixer_function(utilityPath, symbolsPath):
 
         def stack_fixer_function(line):
             return stack_fixer_module.fixSymbols(
-                line, slowWarning=True, breakpadSymsDir=symbolsPath)
+                line, slowWarning=True, breakpadSymsDir=symbolsPath, hide_errors=hideErrors)
 
     elif mozinfo.isLinux or mozinfo.isMac or mozinfo.isWin:
         # Run each line through fix_stacks.py. This method is preferred for
@@ -262,7 +262,7 @@ def get_stack_fixer_function(utilityPath, symbolsPath):
         stack_fixer_module = import_stack_fixer_module('fix_stacks')
 
         def stack_fixer_function(line):
-            return stack_fixer_module.fixSymbols(line, slowWarning=True)
+            return stack_fixer_module.fixSymbols(line, slowWarning=True, hide_errors=hideErrors)
 
     else:
         return None

testing/web-platform/tests/tools/wptrunner/wptrunner/browsers/firefox.py

@@ -428,8 +428,11 @@ class OutputHandler(object):
 
         self.symbols_path = symbols_path
         if stackfix_dir:
+            # We hide errors because they cause disconcerting `CRITICAL`
+            # warnings in web platform test output.
             self.stack_fixer = get_stack_fixer_function(stackfix_dir,
-                                                        self.symbols_path)
+                                                        self.symbols_path,
+                                                        hideErrors=True)
         else:
             self.stack_fixer = None
         self.asan = asan

tools/rb/fix_stacks.py

@@ -21,7 +21,7 @@ line_re = re.compile("#\d+: .+\[.+ \+0x[0-9A-Fa-f]+\]")
 fix_stacks = None
 
 
-def fixSymbols(line, jsonMode=False, slowWarning=False, breakpadSymsDir=None):
+def fixSymbols(line, jsonMode=False, slowWarning=False, breakpadSymsDir=None, hide_errors=False):
     global fix_stacks
 
     result = line_re.search(line)
@@ -59,7 +59,10 @@ def fixSymbols(line, jsonMode=False, slowWarning=False, breakpadSymsDir=None):
             args.append('-b')
             args.append(breakpadSymsDir + "," + fileid_exe)
 
-        fix_stacks = Popen(args, stdin=PIPE, stdout=PIPE, stderr=None)
+        # Sometimes we need to prevent errors from going to stderr.
+        stderr = open(os.devnull) if hide_errors else None
+
+        fix_stacks = Popen(args, stdin=PIPE, stdout=PIPE, stderr=stderr)
 
         if slowWarning:
             print("Initializing stack-fixing for the first stack frame, this may take a while...")