fix: add :enabled sub-config for fixer tools

This allows distributing opt-in fixer tool configurations in .hgrc
files. This may be useful for adding default configs in core, or for
orgranizations that want to provide configs to their users.

Tools are still enabled by default because it would be confusing to add a
config and find that it has no effect until you add enabled=true.

Differential Revision: https://phab.mercurial-scm.org/D6975

hgext/fix.py

@@ -173,6 +173,7 b' FIXER_ATTRS = {'
     'priority': 0,
     'metadata': 'false',
     'skipclean': 'true',
+    'enabled': 'true',
 }
 
 for key, default in FIXER_ATTRS.items():
@@ -726,6 +727,7 b' def getfixers(ui):'
         fixers[name]._priority = int(fixers[name]._priority)
         fixers[name]._metadata = stringutil.parsebool(fixers[name]._metadata)
         fixers[name]._skipclean = stringutil.parsebool(fixers[name]._skipclean)
+        fixers[name]._enabled = stringutil.parsebool(fixers[name]._enabled)
         # Don't use a fixer if it has no pattern configured. It would be
         # dangerous to let it affect all files. It would be pointless to let it
         # affect no files. There is no reasonable subset of files to use as the
@@ -734,6 +736,9 b' def getfixers(ui):'
             ui.warn(
                 _('fixer tool has no pattern configuration: %s\n') % (name,))
             del fixers[name]
+        elif not fixers[name]._enabled:
+            ui.debug('ignoring disabled fixer tool: %s\n' % (name,))
+            del fixers[name]
     return collections.OrderedDict(
         sorted(fixers.items(), key=lambda item: item[1]._priority,
                reverse=True))

tests/test-fix.t

@@ -1341,6 +1341,22 b' pattern config is missing, and that we o'
 
   $ cd ..
 
+Tools can be disabled. Disabled tools do nothing but print a debug message.
+
+  $ hg init disabled
+  $ cd disabled
+
+  $ printf "foo\n" > foo
+  $ hg add -q
+  $ hg fix --debug --working-dir --config "fix.disabled:command=echo fixed" \
+  >                              --config "fix.disabled:pattern=foo" \
+  >                              --config "fix.disabled:enabled=false"
+  ignoring disabled fixer tool: disabled
+  $ cat foo
+  foo
+
+  $ cd ..
+
 Test that we can configure a fixer to affect all files regardless of the cwd.
 The way we invoke matching must not prohibit this.