Merge branch 'jt/diff-color-move-fix'

A handful of bugfixes and an improvement to "diff --color-moved".

* jt/diff-color-move-fix:
  diff: define block by number of alphanumeric chars
  diff: respect MIN_BLOCK_LENGTH for last block
  diff: avoid redundantly clearing a flag

Author: gitster

Documentation/diff-options.txt

@@ -254,13 +254,11 @@ plain::
 	moved line, but it is not very useful in a review to determine
 	if a block of code was moved without permutation.
 zebra::
-	Blocks of moved code are detected greedily. The detected blocks are
+	Blocks of moved text of at least 20 alphanumeric characters
+	are detected greedily. The detected blocks are
 	painted using either the 'color.diff.{old,new}Moved' color or
 	'color.diff.{old,new}MovedAlternative'. The change between
-	the two colors indicates that a new block was detected. If there
-	are fewer than 3 adjacent moved lines, they are not marked up
-	as moved, but the regular colors 'color.diff.{old,new}' will be
-	used.
+	the two colors indicates that a new block was detected.
 dimmed_zebra::
 	Similar to 'zebra', but additional dimming of uninteresting parts
 	of moved code is performed. The bordering lines of two adjacent

diff.c

@@ -855,6 +855,38 @@ static int shrink_potential_moved_blocks(struct moved_entry **pmb,
 	return rp + 1;
 }
 
+/*
+ * If o->color_moved is COLOR_MOVED_PLAIN, this function does nothing.
+ *
+ * Otherwise, if the last block has fewer alphanumeric characters than
+ * COLOR_MOVED_MIN_ALNUM_COUNT, unset DIFF_SYMBOL_MOVED_LINE on all lines in
+ * that block.
+ *
+ * The last block consists of the (n - block_length)'th line up to but not
+ * including the nth line.
+ *
+ * NEEDSWORK: This uses the same heuristic as blame_entry_score() in blame.c.
+ * Think of a way to unify them.
+ */
+static void adjust_last_block(struct diff_options *o, int n, int block_length)
+{
+	int i, alnum_count = 0;
+	if (o->color_moved == COLOR_MOVED_PLAIN)
+		return;
+	for (i = 1; i < block_length + 1; i++) {
+		const char *c = o->emitted_symbols->buf[n - i].line;
+		for (; *c; c++) {
+			if (!isalnum(*c))
+				continue;
+			alnum_count++;
+			if (alnum_count >= COLOR_MOVED_MIN_ALNUM_COUNT)
+				return;
+		}
+	}
+	for (i = 1; i < block_length + 1; i++)
+		o->emitted_symbols->buf[n - i].flags &= ~DIFF_SYMBOL_MOVED_LINE;
+}
+
 /* Find blocks of moved code, delegate actual coloring decision to helper */
 static void mark_color_as_moved(struct diff_options *o,
 				struct hashmap *add_lines,
@@ -890,20 +922,13 @@ static void mark_color_as_moved(struct diff_options *o,
 		}
 
 		if (!match) {
-			if (block_length < COLOR_MOVED_MIN_BLOCK_LENGTH &&
-			    o->color_moved != COLOR_MOVED_PLAIN) {
-				for (i = 0; i < block_length + 1; i++) {
-					l = &o->emitted_symbols->buf[n - i];
-					l->flags &= ~DIFF_SYMBOL_MOVED_LINE;
-				}
-			}
+			adjust_last_block(o, n, block_length);
 			pmb_nr = 0;
 			block_length = 0;
 			continue;
 		}
 
 		l->flags |= DIFF_SYMBOL_MOVED_LINE;
-		block_length++;
 
 		if (o->color_moved == COLOR_MOVED_PLAIN)
 			continue;
@@ -933,11 +958,17 @@ static void mark_color_as_moved(struct diff_options *o,
 			}
 
 			flipped_block = (flipped_block + 1) % 2;
+
+			adjust_last_block(o, n, block_length);
+			block_length = 0;
 		}
 
+		block_length++;
+
 		if (flipped_block)
 			l->flags |= DIFF_SYMBOL_MOVED_LINE_ALT;
 	}
+	adjust_last_block(o, n, block_length);
 
 	free(pmb);
 }

diff.h

@@ -195,7 +195,7 @@ struct diff_options {
 		COLOR_MOVED_ZEBRA_DIM = 3,
 	} color_moved;
 	#define COLOR_MOVED_DEFAULT COLOR_MOVED_ZEBRA
-	#define COLOR_MOVED_MIN_BLOCK_LENGTH 3
+	#define COLOR_MOVED_MIN_ALNUM_COUNT 20
 };
 
 void diff_emit_submodule_del(struct diff_options *o, const char *line);