diff mercurial/filemerge.py @ 39125:cded904f7acc

filemerge: add config knob to check capabilities of internal merge tools

For historical reason, Mercurial assumes capabilities of internal
merge tools as below while examining rules to decide merge tool,
regardless of actual capabilities of them.

    =============== ====== ========
    specified via   binary symlinks
    =============== ====== ========
    --tool          o      o
    HGMERGE         o      o
    merge-patterns  o (*)  x (*)
    ui.merge        x (*)  x (*)
    =============== ====== ========

This causes:

  - unintentional internal merge tool is chosen for binary files via
    merge-patterns section of configuration file

  - explicit configuration of internal merge tool for symlinks is
    ignored unintentionally

But on the other hand, simple "check capability strictly" might break
backward compatibility (e.g. existing merge automations), because it
changes the result of merge tool selection.

Therefore, this patch adds config knob "merge.strict-capability-check"
to control whether capabilities of internal merge tools should be
checked strictly or not.

If this configuration is true, capabilities of internal merge tools
are checked strictly in (*) cases above.

--- a/mercurial/filemerge.py	Wed Aug 15 22:24:38 2018 +0900
+++ b/mercurial/filemerge.py	Wed Aug 15 22:24:50 2018 +0900
@@ -137,6 +137,8 @@
     return procutil.findexe(util.expandpath(exe))
 
 def _picktool(repo, ui, path, binary, symlink, changedelete):
+    strictcheck = ui.configbool('merge', 'strict-capability-check')
+
     def hascapability(tool, capability, strict=False):
         if strict and tool in internals:
             if internals[tool].capabilities.get(capability):
@@ -155,9 +157,9 @@
                 ui.warn(_("couldn't find merge tool %s\n") % tmsg)
             else: # configured but non-existing tools are more silent
                 ui.note(_("couldn't find merge tool %s\n") % tmsg)
-        elif symlink and not hascapability(tool, "symlink"):
+        elif symlink and not hascapability(tool, "symlink", strictcheck):
             ui.warn(_("tool %s can't handle symlinks\n") % tmsg)
-        elif binary and not hascapability(tool, "binary"):
+        elif binary and not hascapability(tool, "binary", strictcheck):
             ui.warn(_("tool %s can't handle binary\n") % tmsg)
         elif changedelete and not supportscd(tool):
             # the nomerge tools are the only tools that support change/delete
@@ -192,9 +194,13 @@
             return (hgmerge, hgmerge)
 
     # then patterns
+
+    # whether binary capability should be checked strictly
+    binarycap = binary and strictcheck
+
     for pat, tool in ui.configitems("merge-patterns"):
         mf = match.match(repo.root, '', [pat])
-        if mf(path) and check(tool, pat, symlink, False, changedelete):
+        if mf(path) and check(tool, pat, symlink, binarycap, changedelete):
             if binary and not hascapability(tool, "binary", strict=True):
                 ui.warn(_("warning: check merge-patterns configurations,"
                           " if %r for binary file %r is unintentional\n"