[src/trunk]: src/usr.bin/make make: document interaction between cmdline and ...

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

details:   https://anonhg.NetBSD.org/src/rev/c933aee7e5a9
branches:  trunk
changeset: 952975:c933aee7e5a9
user:      rillig <rillig%NetBSD.org@localhost>
date:      Mon Feb 22 21:14:15 2021 +0000

description:
make: document interaction between cmdline and global variables

Make prevents global variables from being or becoming visible when a
command line variable of the same name is already defined.

There is a double safety net here.  Even if the call to Var_DeleteExpand
were removed, there would be no noticeable effect, other than one less
line in the debug log.

No functional change.

diffstat:

 usr.bin/make/var.c |  14 ++++++++++++--
 1 files changed, 12 insertions(+), 2 deletions(-)

diffs (42 lines):

diff -r 0cb30e00fa40 -r c933aee7e5a9 usr.bin/make/var.c
--- a/usr.bin/make/var.c        Mon Feb 22 20:45:46 2021 +0000
+++ b/usr.bin/make/var.c        Mon Feb 22 21:14:15 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: var.c,v 1.831 2021/02/16 19:46:15 rillig Exp $ */
+/*     $NetBSD: var.c,v 1.832 2021/02/22 21:14:15 rillig Exp $ */
 
 /*
  * Copyright (c) 1988, 1989, 1990, 1993
@@ -140,7 +140,7 @@
 #include "metachar.h"
 
 /*     "@(#)var.c      8.3 (Berkeley) 3/19/94" */
-MAKE_RCSID("$NetBSD: var.c,v 1.831 2021/02/16 19:46:15 rillig Exp $");
+MAKE_RCSID("$NetBSD: var.c,v 1.832 2021/02/22 21:14:15 rillig Exp $");
 
 typedef enum VarFlags {
        VFL_NONE        = 0,
@@ -945,6 +945,14 @@
        if (scope == SCOPE_GLOBAL) {
                v = VarFind(name, SCOPE_CMDLINE, FALSE);
                if (v != NULL) {
+                       /*
+                        * When there is a variable of the same name in the
+                        * command line scope, the global variable would not
+                        * be visible anywhere.  Therefore there is no point
+                        * in setting it at all.
+                        *
+                        * See 'scope == SCOPE_CMDLINE' below.
+                        */
                        if (v->flags & VFL_FROM_CMD) {
                                DEBUG3(VAR, "%s:%s = %s ignored!\n",
                                    scope->name, name, val);
@@ -966,6 +974,8 @@
                         * This var would normally prevent the same name being
                         * added to SCOPE_GLOBAL, so delete it from there if
                         * needed. Otherwise -V name may show the wrong value.
+                        *
+                        * See 'scope == SCOPE_GLOBAL' above.
                         */
                        /* XXX: name is expanded for the second time */
                        Var_DeleteExpand(SCOPE_GLOBAL, name);