[PATCH V2] ui: add new config flag for interface selection

[Laurent Charignon]

# HG changeset patch
# User Laurent Charignon <lcharignon at fb.com>
# Date 1454635156 28800
#      Thu Feb 04 17:19:16 2016 -0800
# Branch stable
# Node ID 229eebf1a275b253f6b8a2ea509b52ccce3e3f83
# Parent  b163d0993d788fb7c5a55a8a052b1115ba7b66e6
ui: add new config flag for interface selection

This patch introduces a new config flag ui.interface to select the interface
for interactive commands. It currently only applies to chunks selection.
The config can be overridden on a per feature basis with the flag
ui.interface.<feature>.

features for the moment can only be 'chunkselector', moving forward we expect
to have 'histedit' and other commands there.

If an incorrect value is given to ui.interface we print a warning and use the
default interface: text. If HGPLAIN is specified we also use the default
interface: text.

diff --git a/mercurial/help/config.txt b/mercurial/help/config.txt
--- a/mercurial/help/config.txt
+++ b/mercurial/help/config.txt
@@ -1587,6 +1587,17 @@
 ``interactive``
     Allow to prompt the user. (default: True)
 
+``interface``
+    Select the default interface for interactive features (default: text).
+    Possible values are 'text' and 'curses'.
+
+``interface.chunkselector``
+    Select the interface for chunkselection.
+    Possible values are 'text' and 'crecord'.
+    This config overrides the interface specified by ui.interface.
+    If ui.interface and ui.interface.chunkselector aren't set, we use the text
+    interface.
+
 ``logtemplate``
     Template string for commands that print changesets.
 
diff --git a/mercurial/ui.py b/mercurial/ui.py
--- a/mercurial/ui.py
+++ b/mercurial/ui.py
@@ -699,6 +699,63 @@
             return False
         return util.isatty(fh)
 
+    def interface(self, feature):
+        '''what interface to use for interactive console features?
+
+        The interface is controlled by the value of `ui.interface` but also by
+        the value of feature-specific configuration. For example:
+
+        ui.interface.histedit = text
+        ui.interface.chunkselector = crecord
+
+        Here the features are "histedit" and "chunkselector".
+
+        The configuration above means that the default interfaces for commands
+        is curses, the interface for histedit is text and the interface for
+        selecting chunk is crecord (a curses interface).
+
+        Consider the following exemple:
+        ui.interface = curses
+        ui.interface.histedit = text
+
+        Then histedit will use the text interface and chunkselector will use
+        the default curses interface (crecord at the moment).
+        '''
+        if self.plain():
+            return "text"
+
+        alloweddefaultinterfaces = ("text", "curses")
+        defaultfeaturesinterfaces = {
+            "chunkselector": {
+                "text": "text",
+                "curses": "crecord"
+            }
+        }
+
+        # Default interface
+        defaultinterface = "text"
+        i = self.config("ui", "interface", None)
+        if i is not None:
+            if i not in alloweddefaultinterfaces:
+                self.warn(_("invalid value for ui.interface: %s") % i)
+                self.warn(_("(using default interface instead %s)")
+                          % defaultinterface)
+            else:
+                defaultinterface = i
+
+        # Feature-specific interface
+        if feature not in defaultfeaturesinterfaces.keys():
+            # This is a programming error, not a user facing error, it is
+            # ok to Abort here as we should never hit this case
+            raise ValueError("Unknown feature requested %s" % feature)
+
+        f = self.config("ui", "interface.%s" % feature, None)
+        if f is None:
+            return defaultfeaturesinterfaces[feature][defaultinterface]
+        else:
+            return f
+
+
     def interactive(self):
         '''is interactive input allowed?
 
diff --git a/tests/test-commit-interactive-curses.t b/tests/test-commit-interactive-curses.t
--- a/tests/test-commit-interactive-curses.t
+++ b/tests/test-commit-interactive-curses.t
@@ -223,3 +223,34 @@
   hello world
 
 
+Check ui.interface logic for the chunkselector
+
+The default interface is text
+  $ chunkselectorinterface() {
+  > python <<EOF
+  > from mercurial import hg, ui, parsers;\
+  > repo = hg.repository(ui.ui(), ".");\
+  > print repo.ui.interface("chunkselector")
+  > EOF
+  > }
+  $ chunkselectorinterface
+  text
+
+The default curses interface is crecord
+  $ cat <<EOF >> $HGRCPATH
+  > [ui]
+  > interface = curses
+  > EOF
+  $ chunkselectorinterface
+  crecord
+
+It is possible to override the default interface with a feature specific
+interface
+  $ cat <<EOF >> $HGRCPATH
+  > [ui]
+  > interface = text
+  > interface.chunkselector = crecord
+  > EOF
+
+  $ chunkselectorinterface
+  crecord