tree edcc1e440e36ac29ac90250356ff4e9fa3e50d8c
parent ead57c3004fea4dede45a4005d7789eef7d18749
author David Benjamin <davidben@google.com> 1628101735 -0400
committer Adam Langley <agl@google.com> 1628188624 +0000

Avoid double-expanding variables in CMake.

CMake's language is rather fragile and unsound. For the most part, it is
a shell script with more parentheses. That is, it simply expands command
arguments into a list of strings and then evaluates it, complete with
shell-style differences between "${FOO}" and ${FOO}.

The if() command is special and internally also expands variables. That
is why things like if(FOO STREQUAL "BAR") work. CMake interprets "FOO"
as a variable if it can find a variable, or a string otherwise. In
addition to getting very confused on typos, it means that
if("${FOO}" STREQUAL "BAR") will double-expand, and it will do strange
things if BAR is a variable.

CMP0054 patches this (which we set by minimum version) so that if() only
expands if the token was unquoted. This fixes
if("${FOO}" STREQUAL "BAR"). However, if(${FOO} STREQUAL "BAR")
continues to double-expand FOO.

We had a mix of all three of FOO, ${FOO}, and "${FOO}". It's not clear
which is the canonical spelling at this point, but CMake own files
(mostly) use FOO, as do most of our lines, so I've standardized on that.
It's a little unsatisfying if we typo a variable, but I suppose ${FOO}
also silently ignores unset variables.

Bug: 423
Change-Id: Ib6baa27f4065eed159e8fb28820b71a0c99e0db0
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/48705
Reviewed-by: Adam Langley <agl@google.com>