diff --git a/mercurial/diffutil.py b/mercurial/diffutil.py
--- a/mercurial/diffutil.py
+++ b/mercurial/diffutil.py
@@ -30,8 +30,15 @@
     - whitespace: whitespace options like ignoreblanklines and ignorews
     - formatchanging: options that will likely break or cause correctness issues
       with most diff parsers
+
+    For the category settings (whitespace, git, formatchanging), the valid
+    values are True, False, or the string 'noconfig'. If the string 'noconfig'
+    is used, then only values in `opts` are considered, otherwise this returns
+    False (which is the default value for all options besides 'unified', which
+    does not set 'category').
     '''
-    def get(key, name=None, getter=ui.configbool, forceplain=None):
+    def get(key, name=None, getter=ui.configbool, forceplain=None,
+            category=None):
         if opts:
             v = opts.get(key)
             # diffopts flags are either None-default (which is passed
@@ -45,6 +52,8 @@
                 return v
         if forceplain is not None and ui.plain():
             return forceplain
+        if category == 'noconfig':
+            return False
         return getter(section, name or key, untrusted=untrusted)
 
     # core options, expected to be understood by every diff parser
@@ -56,7 +65,7 @@
     buildopts['xdiff'] = ui.configbool('experimental', 'xdiff')
 
     if git:
-        buildopts['git'] = get('git')
+        buildopts['git'] = get('git', category=git)
 
         # since this is in the experimental section, we need to call
         # ui.configbool directory
@@ -88,18 +97,25 @@
                 buildopts['index'] = hlen
 
     if whitespace:
-        buildopts['ignorews'] = get('ignore_all_space', 'ignorews')
-        buildopts['ignorewsamount'] = get('ignore_space_change',
+        getws = lambda *args, **kwargs: get(*args, category=whitespace,
+                                            **kwargs)
+
+        buildopts['ignorews'] = getws('ignore_all_space', 'ignorews')
+        buildopts['ignorewsamount'] = getws('ignore_space_change',
                                           'ignorewsamount')
-        buildopts['ignoreblanklines'] = get('ignore_blank_lines',
+        buildopts['ignoreblanklines'] = getws('ignore_blank_lines',
                                             'ignoreblanklines')
-        buildopts['ignorewseol'] = get('ignore_space_at_eol', 'ignorewseol')
+        buildopts['ignorewseol'] = getws('ignore_space_at_eol', 'ignorewseol')
     if formatchanging:
+        getfc = lambda *args, **kwargs: get(*args, category=formatchanging,
+                                            **kwargs)
+
         buildopts['text'] = opts and opts.get('text')
         binary = None if opts is None else opts.get('binary')
         buildopts['nobinary'] = (not binary if binary is not None
-                                 else get('nobinary', forceplain=False))
-        buildopts['noprefix'] = get('noprefix', forceplain=False)
-        buildopts['worddiff'] = get('word_diff', 'word-diff', forceplain=False)
+                                 else getfc('nobinary', forceplain=False))
+        buildopts['noprefix'] = getfc('noprefix', forceplain=False)
+        buildopts['worddiff'] = getfc('word_diff', 'word-diff',
+                                      forceplain=False)
 
     return mdiff.diffopts(**pycompat.strkwargs(buildopts))