[src/trunk]: src/usr.bin/make/unit-tests tests/make: test hash code collision...

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

details:   https://anonhg.NetBSD.org/src/rev/5318108d16e5
branches:  trunk
changeset: 359845:5318108d16e5
user:      rillig <rillig%NetBSD.org@localhost>
date:      Thu Jan 27 10:42:02 2022 +0000

description:
tests/make: test hash code collisions of variable names

In HashEntry_KeyEquals, the line 'return false' was not covered by any
tests before.  Since it is an edge case that two variable names (or
other keys) have the same 32-bit hash code and still differ, better test
for that edge case explicitly since a bug in this place would be rare
and hard to find.

diffstat:

 usr.bin/make/unit-tests/varname.mk |  44 +++++++++++++++++++++++++++++++++++++-
 1 files changed, 43 insertions(+), 1 deletions(-)

diffs (56 lines):

diff -r 11df6a625379 -r 5318108d16e5 usr.bin/make/unit-tests/varname.mk
--- a/usr.bin/make/unit-tests/varname.mk        Thu Jan 27 10:34:55 2022 +0000
+++ b/usr.bin/make/unit-tests/varname.mk        Thu Jan 27 10:42:02 2022 +0000
@@ -1,4 +1,4 @@
-# $NetBSD: varname.mk,v 1.8 2020/11/02 22:59:48 rillig Exp $
+# $NetBSD: varname.mk,v 1.9 2022/01/27 10:42:02 rillig Exp $
 #
 # Tests for special variables, such as .MAKE or .PARSEDIR.
 # And for variable names in general.
@@ -41,4 +41,46 @@
 
 .MAKEFLAGS: -d0
 
+# All variable names of a scope are stored in the same hash table, using a
+# simple hash function.  Ensure that HashEntry_KeyEquals handles collisions
+# correctly and that the correct variable is looked up.  The strings "0x" and
+# "1Y" have the same hash code, as 31 * '0' + 'x' == 31 * '1' + 'Y'.
+V.0x=  0x
+V.1Y=  1Y
+.if ${V.0x} != "0x" || ${V.1Y} != "1Y"
+.  error
+.endif
+
+# The string "ASDZguv", when used as a prefix of a variable name, keeps the
+# hash code unchanged, its own hash code is 0.
+ASDZguvV.0x=   0x
+ASDZguvV.1Y=   1Y
+.if ${ASDZguvV.0x} != "0x"
+.  error
+.elif ${ASDZguvV.1Y} != "1Y"
+.  error
+.endif
+
+# Ensure that variables with the same hash code whose name is a prefix of the
+# other can be accessed.  In this case, the shorter variable name is defined
+# first to make it appear later in the bucket of the hash table.
+ASDZguv=       once
+ASDZguvASDZguv=        twice
+.if ${ASDZguv} != "once"
+.  error
+.elif ${ASDZguvASDZguv} != "twice"
+.  error
+.endif
+
+# Ensure that variables with the same hash code whose name is a prefix of the
+# other can be accessed.  In this case, the longer variable name is defined
+# first to make it appear later in the bucket of the hash table.
+ASDZguvASDZguv.param=  twice
+ASDZguv.param=         once
+.if ${ASDZguv.param} != "once"
+.  error
+.elif ${ASDZguvASDZguv.param} != "twice"
+.  error
+.endif
+
 all: