changeset_printer: change flush() to accept ctx instead of rev

Because flush() is the function to write data buffered by show(ctx),
flush(ctx) is more consistent than flush(rev). This makes sure that
buffered header and hunk are always keyed by ctx.rev().

This patch will allow us to give an integer to the wdir while keeping
wctx.rev() -> None.

mercurial/cmdutil.py

@@ -1119,7 +1119,8 b' class changeset_printer(object):'
         self.lastheader = None
         self.footer = None
 
-    def flush(self, rev):
+    def flush(self, ctx):
+        rev = ctx.rev()
         if rev in self.header:
             h = self.header[rev]
             if h != self.lastheader:
@@ -2156,7 +2157,7 b' def displaygraph(ui, dag, displayer, sho'
         lines = displayer.hunk.pop(rev).split('\n')
         if not lines[-1]:
             del lines[-1]
-        displayer.flush(rev)
+        displayer.flush(ctx)
         edges = edgefn(type, char, lines, seen, rev, parents)
         for type, char, lines, coldata in edges:
             graphmod.ascii(ui, state, type, char, lines, coldata)

mercurial/commands.py

@@ -4627,7 +4627,7 b' def log(ui, repo, *pats, **opts):'
         else:
             revmatchfn = None
         displayer.show(ctx, copies=copies, matchfn=revmatchfn)
-        if displayer.flush(rev):
+        if displayer.flush(ctx):
             count += 1
 
     displayer.close()