merge-ort: allow rename detection to be disabled

When merge-ort was written, I did not at first allow rename detection to
be disabled, because I suspected that most folks disabling rename
detection were doing so solely for performance reasons.  Since I put a
lot of working into providing dramatic speedups for rename detection
performance as used by the merge machinery, I wanted to know if there
were still real world repositories where rename detection was
problematic from a performance perspective.  We have had years now to
collect such information, and while we never received one, waiting
longer with the option disabled seems unlikely to help surface such
issues at this point.  Also, there has been at least one request to
allow rename detection to be disabled for behavioral rather than
performance reasons, so let's start heeding the config and command line
settings.

Signed-off-by: Elijah Newren <[email protected]>

Author: newren

Documentation/merge-strategies.adoc

@@ -82,6 +82,11 @@ find-renames[=<n>];;
 rename-threshold=<n>;;
 	Deprecated synonym for `find-renames=<n>`.
 
+no-renames;;
+	Turn off rename detection. This overrides the `merge.renames`
+	configuration variable.
+	See also linkgit:git-diff[1] `--no-renames`.
+
 subtree[=<path>];;
 	This option is a more advanced form of 'subtree' strategy, where
 	the strategy makes a guess on how two trees must be shifted to
@@ -107,7 +112,7 @@ For a path that is a submodule, the same caution as 'ort' applies to this
 strategy.
 +
 The 'recursive' strategy takes the same options as 'ort'.  However,
-there are three additional options that 'ort' ignores (not documented
+there are two additional options that 'ort' ignores (not documented
 above) that are potentially useful with the 'recursive' strategy:
 
 patience;;
@@ -121,11 +126,6 @@ diff-algorithm=[patience|minimal|histogram|myers];;
 	specifically uses `diff-algorithm=histogram`, while `recursive`
 	defaults to the `diff.algorithm` config setting.
 
-no-renames;;
-	Turn off rename detection. This overrides the `merge.renames`
-	configuration variable.
-	See also linkgit:git-diff[1] `--no-renames`.
-
 resolve::
 	This can only resolve two heads (i.e. the current branch
 	and another branch you pulled from) using a 3-way merge

merge-ort.c

@@ -3448,6 +3448,11 @@ static int detect_and_process_renames(struct merge_options *opt)
 
 	if (!possible_renames(renames))
 		goto cleanup;
+	if (opt->detect_renames == 0) {
+		renames->redo_after_renames = 0;
+		renames->cached_pairs_valid_side = 0;
+		goto cleanup;
+	}
 
 	trace2_region_enter("merge", "regular renames", opt->repo);
 	detection_run |= detect_regular_renames(opt, MERGE_SIDE1);