[src/trunk]: src/usr.bin/make make(1): document almost duplicate code

[rillig <rillig%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/87f06c742677
branches:  trunk
changeset: 936721:87f06c742677
user:      rillig <rillig%NetBSD.org@localhost>
date:      Sun Aug 02 10:49:53 2020 +0000

description:
make(1): document almost duplicate code

ParseModifierPart and Var_Parse are very similar, but there might be
subtle differences.  Until these differences are documented in the form
of unit tests, merging these code pieces is too dangerous.

diffstat:

 usr.bin/make/var.c |  19 ++++++++++++++-----
 1 files changed, 14 insertions(+), 5 deletions(-)

diffs (60 lines):

diff -r b114a3cf6550 -r 87f06c742677 usr.bin/make/var.c
--- a/usr.bin/make/var.c        Sun Aug 02 10:47:09 2020 +0000
+++ b/usr.bin/make/var.c        Sun Aug 02 10:49:53 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: var.c,v 1.395 2020/08/02 10:47:09 rillig Exp $ */
+/*     $NetBSD: var.c,v 1.396 2020/08/02 10:49:53 rillig Exp $ */
 
 /*
  * Copyright (c) 1988, 1989, 1990, 1993
@@ -69,14 +69,14 @@
  */
 
 #ifndef MAKE_NATIVE
-static char rcsid[] = "$NetBSD: var.c,v 1.395 2020/08/02 10:47:09 rillig Exp $";
+static char rcsid[] = "$NetBSD: var.c,v 1.396 2020/08/02 10:49:53 rillig Exp $";
 #else
 #include <sys/cdefs.h>
 #ifndef lint
 #if 0
 static char sccsid[] = "@(#)var.c      8.3 (Berkeley) 3/19/94";
 #else
-__RCSID("$NetBSD: var.c,v 1.395 2020/08/02 10:47:09 rillig Exp $");
+__RCSID("$NetBSD: var.c,v 1.396 2020/08/02 10:49:53 rillig Exp $");
 #endif
 #endif /* not lint */
 #endif
@@ -1746,7 +1746,6 @@
                                 * allow ampersands to be escaped and replace
                                 * unescaped ampersands with subst->lhs. */
 ) {
-    char *rstr;
     Buffer buf;
 
     Buf_InitZ(&buf, 0);
@@ -1798,6 +1797,15 @@
            continue;
        }
 
+       /* XXX: This whole block is very similar to Var_Parse without
+        * VARE_WANTRES.  There may be subtle edge cases though that are
+        * not yet covered in the unit tests and that are parsed differently,
+        * depending on whether they are evaluated or not.
+        *
+        * This subtle difference is not documented in the manual page,
+        * neither is the difference between parsing :D and :M documented.
+        * No code should ever depend on these details, but who knows. */
+
        const char *varstart = p;       /* Nested variable, only parsed */
        if (p[1] == PROPEN || p[1] == BROPEN) {
            /*
@@ -1832,7 +1840,8 @@
     *pp = ++p;
     if (out_length != NULL)
        *out_length = Buf_Size(&buf);
-    rstr = Buf_Destroy(&buf, FALSE);
+
+    char *rstr = Buf_Destroy(&buf, FALSE);
     if (DEBUG(VAR))
        fprintf(debug_file, "Modifier part: \"%s\"\n", rstr);
     return rstr;