diff: retain original file names

When diffing non-regular files, like /dev/null,
pipes, and similar, diff will generate a temp
file to diff against. This is the right thing
to do, but the temp file leaks into the diff.

This patch retains the original file name all
the way through to diff output.

sys/src/cmd/diff/diff.h

@@ -23,8 +23,8 @@ void *emalloc(unsigned);
 void *erealloc(void *, unsigned);
 void diff(char *, char *, int);
 void diffdir(char *, char *, int);
-void diffreg(char *, char *);
+void diffreg(char *, char *, char *, char *);
-Biobuf *prepare(int, char *);
+Biobuf *prepare(int, char *, char *);
 void panic(int, char *, ...);
 void check(Biobuf *, Biobuf *);
 void change(int, int, int, int);

sys/src/cmd/diff/diffio.c

@@ -104,7 +104,7 @@ readhash(Biobuf *bp, char *buf)
 }
 
 Biobuf *
-prepare(int i, char *arg)
+prepare(int i, char *arg, char *orig)
 {
 	Line *p;
 	int j, h;
@@ -143,11 +143,10 @@ prepare(int i, char *arg)
 	file[i] = p;
 	input[i] = bp;			/*fix*/
 	if (i == 0) {			/*fix*/
-		file1 = arg;
+		file1 = orig;
 		firstchange = 0;
-	}
+	} else
-	else
+		file2 = orig;
-		file2 = arg;
 	return bp;
 }
 

sys/src/cmd/diff/diffreg.c

@@ -363,16 +363,16 @@ cmp(Biobuf* b1, Biobuf* b2)
 }
 
 void
-diffreg(char *f, char *t)
+diffreg(char *f, char *fo, char *t, char *to)
 {
 	Biobuf *b0, *b1;
 	int k;
 
 	binary = 0;
-	b0 = prepare(0, f);
+	b0 = prepare(0, f, fo);
 	if (!b0)
 		return;
-	b1 = prepare(1, t);
+	b1 = prepare(1, t, to);
 	if (!b1) {
 		Bterm(b0);
 		return;

sys/src/cmd/diff/main.c

@@ -149,7 +149,7 @@ diff(char *f, char *t, int level)
 			Bprint(&stdout, "Common subdirectories: %s and %s\n", fp, tp);
 	}
 	else if (REGULAR_FILE(fsb) && REGULAR_FILE(tsb))
-		diffreg(fp, tp);
+		diffreg(fp, f, tp, t);
 	else {
 		if (REGULAR_FILE(fsb)) {
 			if ((p = utfrrune(f, '/')) == 0)
@@ -157,14 +157,14 @@ diff(char *f, char *t, int level)
 			else
 				p++;
 			if (mkpathname(tb, tp, p) == 0)
-				diffreg(fp, tb);
+				diffreg(fp, f, tb, t);
 		} else {
 			if ((p = utfrrune(t, '/')) == 0)
 				p = t;
 			else
 				p++;
 			if (mkpathname(fb, fp, p) == 0)
-				diffreg(fb, tp);
+				diffreg(fb, f, tp, t);
 		}
 	}
 	free(fsb);