fix: add suboption for configuring execution order of tools

This could be accomplished by using wrapper scripts, but that would diminish
the usefulness of the incremental formatting logic. Configuring execution order
along with other things in the hgrc is probably more convenient anyway.

This change highlights some awkwardness with suboptions and default values,
which should be addressed separately.

Differential Revision: https://phab.mercurial-scm.org/D5237

hgext/fix.py

@@ -54,6 +54,24 b' will also cause :hg:`fix` to exit with a'
   [fix]
   failure = abort
 
+When multiple tools are configured to affect a file, they execute in an order
+defined by the :priority suboption. The priority suboption has a default value
+of zero for each tool. Tools are executed in order of descending priority. The
+execution order of tools with equal priority is unspecified. For example, you
+could use the 'sort' and 'head' utilities to keep only the 10 smallest numbers
+in a text file by ensuring that 'sort' runs before 'head'::
+
+  [fix]
+  sort:command = sort --numeric-sort
+  head:command = head --lines=10
+  sort:pattern = numbers.txt
+  head:pattern = numbers.txt
+  sort:priority = 2
+  head:priority = 1
+
+To account for changes made by each tool, the line numbers used for incremental
+formatting are recomputed before executing the next tool. So, each tool may see
+different values for the arguments added by the :linerange suboption.
 """
 
 from __future__ import absolute_import
@@ -100,10 +118,16 b' configtable = {}'
 configitem = registrar.configitem(configtable)
 
 # Register the suboptions allowed for each configured fixer.
-FIXER_ATTRS = ('command', 'linerange', 'fileset', 'pattern')
+FIXER_ATTRS = {
+    'command': None,
+    'linerange': None,
+    'fileset': None,
+    'pattern': None,
+    'priority': 0,
+}
 
-for key in FIXER_ATTRS:
-    configitem('fix', '.*(:%s)?' % key, default=None, generic=True)
+for key, default in FIXER_ATTRS.items():
+    configitem('fix', '.*(:%s)?' % key, default=default, generic=True)
 
 # A good default size allows most source code files to be fixed, but avoids
 # letting fixer tools choke on huge inputs, which could be surprising to the
@@ -602,18 +626,21 b' def getfixers(ui):'
     Each value is a Fixer object with methods that implement the behavior of the
     fixer's config suboptions. Does not validate the config values.
     """
-    result = {}
+    fixers = {}
     for name in fixernames(ui):
-        result[name] = Fixer()
+        fixers[name] = Fixer()
         attrs = ui.configsuboptions('fix', name)[1]
         if 'fileset' in attrs and 'pattern' not in attrs:
             ui.warn(_('the fix.tool:fileset config name is deprecated; '
                       'please rename it to fix.tool:pattern\n'))
             attrs['pattern'] = attrs['fileset']
-        for key in FIXER_ATTRS:
-            setattr(result[name], pycompat.sysstr('_' + key),
-                    attrs.get(key, ''))
-    return result
+        for key, default in FIXER_ATTRS.items():
+            setattr(fixers[name], pycompat.sysstr('_' + key),
+                    attrs.get(key, default))
+        fixers[name]._priority = int(fixers[name]._priority)
+    return collections.OrderedDict(
+        sorted(fixers.items(), key=lambda item: item[1]._priority,
+               reverse=True))
 
 def fixernames(ui):
     """Returns the names of [fix] config options that have suboptions"""

tests/test-fix.t

@@ -165,6 +165,26 b' Help text for fix.'
     [fix]
     failure = abort
   
+  When multiple tools are configured to affect a file, they execute in an order
+  defined by the :priority suboption. The priority suboption has a default value
+  of zero for each tool. Tools are executed in order of descending priority. The
+  execution order of tools with equal priority is unspecified. For example, you
+  could use the 'sort' and 'head' utilities to keep only the 10 smallest numbers
+  in a text file by ensuring that 'sort' runs before 'head':
+  
+    [fix]
+    sort:command = sort --numeric-sort
+    head:command = head --lines=10
+    sort:pattern = numbers.txt
+    head:pattern = numbers.txt
+    sort:priority = 2
+    head:priority = 1
+  
+  To account for changes made by each tool, the line numbers used for
+  incremental formatting are recomputed before executing the next tool. So, each
+  tool may see different values for the arguments added by the :linerange
+  suboption.
+  
   list of commands:
   
    fix           rewrite file content in changesets or working directory
@@ -1127,3 +1147,51 b' warning.'
   first
 
   $ cd ..
+
+The execution order of tools can be controlled. This example doesn't work if
+you sort after truncating, but the config defines the correct order while the
+definitions are out of order (which might imply the incorrect order given the
+implementation of fix). The goal is to use multiple tools to select the lowest
+5 numbers in the file.
+
+  $ hg init priorityexample
+  $ cd priorityexample
+
+  $ cat >> .hg/hgrc <<EOF
+  > [fix]
+  > head:command = head --lines=5
+  > head:pattern = numbers.txt
+  > head:priority = 1
+  > sort:command = sort --numeric-sort
+  > sort:pattern = numbers.txt
+  > sort:priority = 2
+  > EOF
+
+  $ printf "8\n2\n3\n6\n7\n4\n9\n5\n1\n0\n" > numbers.txt
+  $ hg add -q
+  $ hg fix -w
+  $ cat numbers.txt
+  0
+  1
+  2
+  3
+  4
+
+And of course we should be able to break this by reversing the execution order.
+Test negative priorities while we're at it.
+
+  $ cat >> .hg/hgrc <<EOF
+  > [fix]
+  > head:priority = -1
+  > sort:priority = -2
+  > EOF
+  $ printf "8\n2\n3\n6\n7\n4\n9\n5\n1\n0\n" > numbers.txt
+  $ hg fix -w
+  $ cat numbers.txt
+  2
+  3
+  6
+  7
+  8
+
+  $ cd ..