dispatch: make "_checkshellalias()" invoke "findcmd()" with "strict=True"

Before this patch, shell alias may be executed by abbreviated command
name unexpectedly, even if abbreviated command name matches also
against the command provided by extension.

For example, "rebate" shell alias is executed by "hg reba", even if
rebase extension (= "rebase" command) is enabled. In this case, "hg
reba" should be aborted because of command name ambiguity.

This patch makes "_checkshellalias()" invoke "cmdutil.findcmd()"
always with "strict=True" (default value).

If abbreviated command name matches against only one shell alias even
after loading extensions, such shell alias will be executed via
"_parse()".

This patch doesn't remove "_checkshellalias()" invocation itself,
because it may prevent shell alias from loading extensions uselessly.

mercurial/dispatch.py

@@ -635,8 +635,7 b' def _checkshellalias(lui, ui, args):'
 
     cmd = args[0]
     try:
-        aliases, entry = cmdutil.findcmd(cmd, cmdtable,
-                                         lui.configbool("ui", "strict"))
+        aliases, entry = cmdutil.findcmd(cmd, cmdtable)
     except (error.AmbiguousCommand, error.UnknownCommand):
         restorecommands()
         return

tests/test-alias.t

@@ -324,6 +324,21 b' shell aliases with escaped $ chars'
   $ hg escaped4 test
   $0 $@
 
+abbreviated name, which matches against both shell alias and the
+command provided extension, should be aborted.
+
+  $ cat >> .hg/hgrc <<EOF
+  > [extensions]
+  > hgext.rebase =
+  > [alias]
+  > rebate = !echo this is rebate
+  > EOF
+  $ hg reba
+  hg: command 'reba' is ambiguous:
+      rebase rebate
+  [255]
+  $ hg rebat
+  this is rebate
 
 invalid arguments