From 03f0068e52c3d32a25348dccacba797301610106 Mon Sep 17 00:00:00 2001
From: Thomas Leonard <talex5@gmail.com>
Date: Tue, 8 May 2012 11:59:08 +0100
Subject: [PATCH] Better message when forcing a version means not using that
 interface at all

---
 tests/Source.xml               |  1 +
 tests/testsolver.py            |  2 +-
 zeroinstall/injector/solver.py | 25 +++++++++++++++----------
 3 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/tests/Source.xml b/tests/Source.xml
index 13b7076..e21b1a4 100644
--- a/tests/Source.xml
+++ b/tests/Source.xml
@@ -22,6 +22,7 @@
   </group>
 
   <implementation id='old' version='0.1' arch='*-src' compile:command='make'>
+    <requires interface='http://foo/Compiler.xml'/>
     <manifest-digest sha1='666'/>
     <archive href='foo' size='10'/>
   </implementation>
diff --git a/tests/testsolver.py b/tests/testsolver.py
index 0f7a17b..81c9657 100755
--- a/tests/testsolver.py
+++ b/tests/testsolver.py
@@ -106,7 +106,7 @@ class TestSolver(BaseTest):
 		justify(foo_binary_uri, foo_src_impls["impossible"],
 				'''There is no possible selection using Binary 3.\nCan't find all required implementations:\n- <Interface http://foo/Binary.xml> -> impossible\n- <Interface http://foo/Compiler.xml> -> None''')
 		justify(compiler.uri, compiler_impls["sha1=999"],
-				'''Compiler 5 is selectable, but using it would produce a less optimal solution overall.\n\nSelecting Compiler 5 would cause these changes:\n\nhttp://foo/Binary.xml: 1.0 -> 0.1''')
+				'''Compiler 5 is selectable, but using it would produce a less optimal solution overall.\n\nThe changes would be:\n\nhttp://foo/Binary.xml: 1.0 to 0.1''')
 
 	def testRecursive(self):
 		iface_cache = self.config.iface_cache
diff --git a/zeroinstall/injector/solver.py b/zeroinstall/injector/solver.py
index 9a123f5..599140d 100644
--- a/zeroinstall/injector/solver.py
+++ b/zeroinstall/injector/solver.py
@@ -734,7 +734,7 @@ class SATSolver(Solver):
 		wanted = "{iface} {version}".format(iface = iface.get_name(), version = impl.get_version())
 
 		# Could a selection involving impl even be valid?
-		if not s.ready:
+		if not s.ready or iface.uri not in s.selections.selections:
 			reasons = s.details.get(iface, [])
 			for (rid, rstr) in reasons:
 				if rid.id == impl.id and rstr is not None:
@@ -742,9 +742,10 @@ class SATSolver(Solver):
 							wanted = wanted,
 							reason = rstr)
 
-			return _("There is no possible selection using {wanted}.\n{reason}").format(
-				wanted = wanted,
-				reason = s.get_failure_reason())
+			if not s.ready:
+				return _("There is no possible selection using {wanted}.\n{reason}").format(
+					wanted = wanted,
+					reason = s.get_failure_reason())
 
 		actual_selection = self.selections.get(iface, None)
 		if actual_selection is not None:
@@ -782,25 +783,29 @@ class SATSolver(Solver):
 								actual = actual_selection.get_version(),
 								why = _ranking_component_reason[i])
 
+		used_impl = iface.uri in s.selections.selections
+
 		# Impl is selectable and ranked higher than the selected version. Selecting it would cause
 		# a problem elsewhere.
 		changes = []
 		for old_iface, old_sel in self.selections.selections.iteritems():
-			if old_iface == iface.uri: continue
+			if old_iface == iface.uri and used_impl: continue
 			new_sel = s.selections.selections.get(old_iface, None)
 			if new_sel is None:
 				changes.append(_("{interface}: no longer used").format(interface = old_iface))
 			elif old_sel.version != new_sel.version:
-				changes.append(_("%s: %s -> %s") % (old_iface, old_sel.version, new_sel.version))
+				changes.append(_("{interface}: {old} to {new}").format(interface = old_iface, old = old_sel.version, new = new_sel.version))
 			elif old_sel.id != new_sel.id:
-				changes.append(_("%s: %s -> %s") % (old_iface, old_sel.id, new_sel.id))
+				changes.append(_("{interface}: {old} to {new}").format(interface = old_iface, old = old_sel.id, new = new_sel.id))
 
 		if changes:
-			changes_text = '\n\n' + _('Selecting {wanted} would cause these changes:').format(
-					wanted = wanted) + '\n\n' + '\n'.join(changes)
+			changes_text = '\n\n' + _('The changes would be:') + '\n\n' + '\n'.join(changes)
 		else:
 			changes_text = ''
 
-		return _("{wanted} is selectable, but using it would produce a less optimal solution overall.").format(wanted = wanted) + changes_text
+		if used_impl:
+			return _("{wanted} is selectable, but using it would produce a less optimal solution overall.").format(wanted = wanted) + changes_text
+		else:
+			return _("If {wanted} were the only option, the best available solution wouldn't use it.").format(wanted = wanted) + changes_text
 
 DefaultSolver = SATSolver
-- 
2.11.4.GIT