dirstate: speed up read and write
read:
- single call to len(st)
- fewer assignments for position tracking
- don't split apart tuple from unpack
- use a literal for the unpack spec
write:
- localize variables and functions
- avoid copied function call
- use % for string concatenation
% file replaced with directory
adding a
% should fail - would corrupt dirstate
abort: file 'a' in dirstate clashes with 'a/a'
% directory replaced with file
adding a/a
% should fail - would corrupt dirstate
abort: directory 'a' already in dirstate
% directory replaced with file
adding b/c/d
% should fail - would corrupt dirstate
abort: directory 'b' already in dirstate