diff(1): docuemnt merge3

sys/man/1/diff

@@ -7,6 +7,9 @@ diff \- differential file comparator
 .B -abcefmnruw
 ]
 .I file1 ... file2
+.PP
+.B merge3
+.I left common right
 .SH DESCRIPTION
 .I Diff
 tells what lines must be changed in two files to bring them
@@ -165,6 +168,44 @@ Except in rare circumstances,
 .I diff
 finds a smallest sufficient set of file
 differences.
+.PP
+Merge3 merges the contents of
+.I left
+and
+.I right
+using
+.I common
+as a common reference between the two files.
+Changes between
+.IR left ,
+.I right
+and
+.I common
+are computed.
+Any change which does not conflict is output directly.
+When a change does conflict, that is to say,
+affects the same lines of the output file,
+then the change is output with conflict markers.
+The conflict markers look like this:
+.IP
+.EX
+leading content
+<<<<<<<<<< leftfile
+this is an edit made
+to the left file
+========== original
+this is the initial content
+========== rightfile
+here is something that was
+written into the right file
+>>>>>>>>>>
+trailing content
+.EE
+.PP
+If no conflicts are detected,
+.I merge3
+exits with a nil status,
+otherwise it exits with a status of "conflicted".
 .SH FILES
 .B /tmp/diff[12]
 .SH SOURCE

sys/src/cmd/diff/merge3.c

@@ -155,11 +155,11 @@ merge(Diff *l, Diff *r)
 				Bprint(&stdout, "========== %s\n", r->file2);
 				fetch(r, r->ixnew, rc->newx, rc->newy, r->input[1], "");
 				Bprint(&stdout, ">>>>>>>>>>\n");
+				status = "conflict";
 			}
 			ln = y+1;
 			il++;
 			ir++;
-			status = "conflict";
 		}else if(rc == nil || (lc != nil && lx < rx)){
 			fetch(l, l->ixold, ln, lc->oldx-1, l->input[0], "");
 			fetch(l, l->ixnew, lc->newx, lc->newy, l->input[1], "");