vfs: make rename avoid ambiguity of file stat if needed In some cases below, renaming from backup is used to restore original contents of a file. If renaming keeps ctime, mtime and size of a file, restoring is overlooked, and old contents cached before restoring isn't invalidated as expected. - failure of transaction before closing (only from '.hg/journal.dirstate') - rollback of previous transaction (from '.hg/undo.*') - failure in dirstateguard scope (from '.hg/dirstate.SUFFIX') To avoid such problem, this patch makes vfs.rename() avoid ambiguity of file stat, if needed. Ambiguity check is executed, only if: - checkambig=True is specified (not all renaming needs ambiguity check), and - destination file exists before renaming This patch is a part of preparation for "Exact Cache Validation Plan": https://www.mercurial-scm.org/wiki/ExactCacheValidationPlan

vfs: make atomictempfile avoid ambiguity of file stat if needed This patch is a part of preparation for "Exact Cache Validation Plan": https://www.mercurial-scm.org/wiki/ExactCacheValidationPlan

util: make atomictempfile avoid ambiguity of file stat if needed Ambiguity check is executed at close(), only if: - atomictempfile is created with checkambig=True, and - target file exists before renaming This restriction avoids performance decrement by needless examination of file stat (for example, filelog doesn't need exact cache validation, even though it uses atomictempfile to write changes out). See description of filestat class for detail about why the logic in this patch works as expected. This patch is a part of preparation for "Exact Cache Validation Plan": https://www.mercurial-scm.org/wiki/ExactCacheValidationPlan