fix: ignore fixer tool configurations that are missing patterns

This is to prevent a crash under the same circumstances.

This is also to avoid data loss due to accidental application of a fixer tool
to all files, if the matching logic somehow changed to that effect. Affecting
all files until otherwise configured would be dangerous, and not very useful.

We shouldn't abort because there may be other fixers, and it may still be
useful to run them without having to adjust configuration. A user might not
feel confident in changing configs, for example.

Differential Revision: https://phab.mercurial-scm.org/D6693

hgext/fix.py

@@ -705,6 +705,14 b' def getfixers(ui):'
             setattr(fixers[name], pycompat.sysstr('_' + key),
                     attrs.get(key, default))
         fixers[name]._priority = int(fixers[name]._priority)
+        # 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
+        # default.
+        if fixers[name]._pattern is None:
+            ui.warn(
+                _('fixer tool has no pattern configuration: %s\n') % (name,))
+            del fixers[name]
     return collections.OrderedDict(
         sorted(fixers.items(), key=lambda item: item[1]._priority,
                reverse=True))
@@ -722,7 +730,8 b' class Fixer(object):'
 
     def affects(self, opts, fixctx, path):
         """Should this fixer run on the file at the given path and context?"""
-        return scmutil.match(fixctx, [self._pattern], opts)(path)
+        return (self._pattern is not None and
+                scmutil.match(fixctx, [self._pattern], opts)(path))
 
     def shouldoutputmetadata(self):
         """Should the stdout of this fixer start with JSON and a null byte?"""

tests/test-fix.t

@@ -1242,6 +1242,26 b' three revisions instead of two.'
 
   $ cd ..
 
+Tools configured without a pattern are ignored. It would be too dangerous to
+run them on all files, because this might happen while testing a configuration
+that also deletes all of the file content. There is no reasonable subset of the
+files to use as a default. Users should be explicit about what files are
+affected by a tool. This test also confirms that we don't crash when the
+pattern config is missing, and that we only warn about it once.
+
+  $ hg init nopatternconfigured
+  $ cd nopatternconfigured
+
+  $ printf "foo" > foo
+  $ printf "bar" > bar
+  $ hg add -q
+  $ hg fix --debug --working-dir --config "fix.nopattern:command=echo fixed"
+  fixer tool has no pattern configuration: nopattern
+  $ cat foo bar
+  foobar (no-eol)
+
+  $ 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.