trydiff: simplify checking for additions

In the body of the loop in trydiff(), there are conditions like:

  addedset or (f in modifiedset and to is None)

The second half of that expression is to account for the fact that
merge-in additions appear as additions. By instead fixing up the sets
of modified and added files to compensate for this fact, we can
simplify the body of the loop. It also fixes one case where the
addedset was checked without the additional check (the "have we
already reported a copy above?" case in the code, also see fixed test
case).

The similar condition with 'removedset' in it seems to have served no
purpose even before this change, so it could have been simplified even
before.

mercurial/patch.py

@@ -1796,6 +1796,12 b' def trydiff(repo, revs, ctx1, ctx2, modi'
         revs = None
 
     modifiedset, addedset, removedset = set(modified), set(added), set(removed)
+    # Fix up modified and added, since merged-in additions appear as
+    # modifications during merges
+    for f in modifiedset.copy():
+        if f not in ctx1:
+            addedset.add(f)
+            modifiedset.remove(f)
     for f in sorted(modified + added + removed):
         to = None
         tn = None
@@ -1807,7 +1813,7 b' def trydiff(repo, revs, ctx1, ctx2, modi'
             tn = getfilectx(f, ctx2).data()
         a, b = f, f
         if opts.git or losedatafn:
-            if f in addedset or (f in modifiedset and to is None):
+            if f in addedset:
                 mode = gitmode[ctx2.flags(f)]
                 if f in copy or f in copyto:
                     if opts.git:
@@ -1843,7 +1849,7 b' def trydiff(repo, revs, ctx1, ctx2, modi'
                 if not opts.git and not tn:
                     # regular diffs cannot represent new empty file
                     losedatafn(f)
-            elif f in removedset or (f in modifiedset and tn is None):
+            elif f in removedset:
                 if opts.git:
                     # have we already reported a copy above?
                     if ((f in copy and copy[f] in addedset

tests/test-shelve.t

@@ -238,12 +238,6 b' ensure that we have a merge with unresol'
   diff --git a/b/b b/b.rename/b
   rename from b/b
   rename to b.rename/b
-  diff --git a/b/b b/b/b
-  deleted file mode 100644
-  --- a/b/b
-  +++ /dev/null
-  @@ -1,1 +0,0 @@
-  -b
   diff --git a/c b/c.copy
   copy from c
   copy to c.copy