[gdb/testsuite] Fix gdb.base/empty-host-env-vars.exp

  On aarch64-linux (debian testing) with test-case
gdb.base/empty-host-env-vars.exp I ran into:
...
(gdb) show index-cache directory^M
The directory of the index cache is "/home/linux/.cache/gdb".^M
(gdb) FAIL: $exp: env_var_name=HOME: show index-cache directory
...

Without changing any environment variables, the value of the index-cache dir
is:
...
$ gdb -q -batch -ex "show index-cache directory"
The directory of the index cache is "/home/linux/.cache/gdb".
...
and the expectation of the test-case is that setting HOME to empty will
produce an empty dir, but what it actually produces is:
...
$ HOME= gdb -q -batch -ex "show index-cache directory"
The directory of the index cache is "/home/linux/.cache/gdb".
...

There's nothing wrong with that behaviour, the dir is simply constructed using
XDG_CACHE_HOME which happens to be explictly set to its default value
$HOME/.cache [1]:
...
$ echo $XDG_CACHE_HOME
/home/linux/.cache
...
and indeed also setting that variable to empty gets us the expected empty dir:
...
$ XDG_CACHE_HOME= HOME= gdb -q -batch -ex "show index-cache directory"
gdb: warning: Couldn't determine a path for the index cache directory.
The directory of the index cache is "".
...

Furthermore, the test-case assumption that setting variables to empty either
produces the original dir or an empty dir is incorrect.

Say that XDG_CACHE_HOME has a non-default value:
...
$ echo $XDG_CACHE_HOME
/home/linux/my-xdg-cache-home
$ gdb -q -batch -ex "show index-cache directory"
The directory of the index cache is "/home/linux/my-xdg-cache-home/gdb".
...
then setting that variable to empty:
...
$ XDG_CACHE_HOME= gdb -q -batch -ex "show index-cache directory"
The directory of the index cache is "/home/linux/.cache/gdb".
...
does change the value of the dir.

Fix this by making the test-case less specific.

While we're at it, factor out regexps re_pre and re_post to make regexps more
readable, and use string_to_regexp to reduce quoting.

Tested on aarch64-linux.

PR testsuite/32132
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32132

[1] https://specifications.freedesktop.org/basedir-spec/latest/index.html#variables
---
 .../gdb.base/empty-host-env-vars.exp          | 32 ++++++-------------
 1 file changed, 9 insertions(+), 23 deletions(-)


base-commit: 5a655b5291b3f56088409d34e9077e98af63de60
  

On 9/1/24 11:15, Tom de Vries wrote:
> On aarch64-linux (debian testing) with test-case
> gdb.base/empty-host-env-vars.exp I ran into:
> ...
> (gdb) show index-cache directory^M
> The directory of the index cache is "/home/linux/.cache/gdb".^M
> (gdb) FAIL: $exp: env_var_name=HOME: show index-cache directory
> ...
> 
> Without changing any environment variables, the value of the index-cache dir
> is:
> ...
> $ gdb -q -batch -ex "show index-cache directory"
> The directory of the index cache is "/home/linux/.cache/gdb".
> ...
> and the expectation of the test-case is that setting HOME to empty will
> produce an empty dir, but what it actually produces is:
> ...
> $ HOME= gdb -q -batch -ex "show index-cache directory"
> The directory of the index cache is "/home/linux/.cache/gdb".
> ...
> 
> There's nothing wrong with that behaviour, the dir is simply constructed using
> XDG_CACHE_HOME which happens to be explictly set to its default value
> $HOME/.cache [1]:
> ...
> $ echo $XDG_CACHE_HOME
> /home/linux/.cache
> ...
> and indeed also setting that variable to empty gets us the expected empty dir:
> ...
> $ XDG_CACHE_HOME= HOME= gdb -q -batch -ex "show index-cache directory"
> gdb: warning: Couldn't determine a path for the index cache directory.
> The directory of the index cache is "".
> ...
> 
> Furthermore, the test-case assumption that setting variables to empty either
> produces the original dir or an empty dir is incorrect.
> 
> Say that XDG_CACHE_HOME has a non-default value:
> ...
> $ echo $XDG_CACHE_HOME
> /home/linux/my-xdg-cache-home
> $ gdb -q -batch -ex "show index-cache directory"
> The directory of the index cache is "/home/linux/my-xdg-cache-home/gdb".
> ...
> then setting that variable to empty:
> ...
> $ XDG_CACHE_HOME= gdb -q -batch -ex "show index-cache directory"
> The directory of the index cache is "/home/linux/.cache/gdb".
> ...
> does change the value of the dir.
> 
> Fix this by making the test-case less specific.
> 
> While we're at it, factor out regexps re_pre and re_post to make regexps more
> readable, and use string_to_regexp to reduce quoting.
> 

Pushed.

Thanks,
- Tom

> Tested on aarch64-linux.
> 
> PR testsuite/32132
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32132
> 
> [1] https://specifications.freedesktop.org/basedir-spec/latest/index.html#variables
> ---
>   .../gdb.base/empty-host-env-vars.exp          | 32 ++++++-------------
>   1 file changed, 9 insertions(+), 23 deletions(-)
> 
> diff --git a/gdb/testsuite/gdb.base/empty-host-env-vars.exp b/gdb/testsuite/gdb.base/empty-host-env-vars.exp
> index e6e9d6e3156..5fab65a3607 100644
> --- a/gdb/testsuite/gdb.base/empty-host-env-vars.exp
> +++ b/gdb/testsuite/gdb.base/empty-host-env-vars.exp
> @@ -21,16 +21,14 @@ require {!is_remote host}
>   
>   set all_env_vars { HOME XDG_CACHE_HOME LOCALAPPDATA XDG_CONFIG_HOME }
>   
> -# Record the initial value of the index-cache directory.
> +set re_pre \
> +    [string_to_regexp {The directory of the index cache is "}]
> +set re_post \
> +    [string_to_regexp {".}]
> +
> +# Show the initial value of the index-cache directory.
>   clean_restart
> -set index_cache_directory ""
> -gdb_test_multiple "show index-cache directory" "" {
> -    -re -wrap "The directory of the index cache is \"(.*)\"\\." {
> -	set index_cache_directory $expect_out(1,string)
> -	set index_cache_directory [string_to_regexp $index_cache_directory]
> -	pass $gdb_test_name
> -    }
> -}
> +gdb_test "show index-cache directory" $re_pre\[^\r\n\]*$re_post
>   
>   foreach_with_prefix env_var_name $all_env_vars {
>       # Restore the original state of the environment variable.
> @@ -38,18 +36,7 @@ foreach_with_prefix env_var_name $all_env_vars {
>   	set env($env_var_name) {}
>   	clean_restart
>   
> -	# Verify that the empty environment variable didn't affect the
> -	# index-cache directory setting, that we still see the initial value.
> -	# "HOME" is different, because if that  one is unset, GDB isn't even
> -	# able to compute the default location.  In that case, we expect it to
> -	# be empty.
> -	if { $env_var_name == "HOME" } {
> -	    gdb_test "show index-cache directory" \
> -		"The directory of the index cache is \"\"\\."
> -	} else {
> -	    gdb_test "show index-cache directory" \
> -		"The directory of the index cache is \"$index_cache_directory\"\\."
> -	}
> +	gdb_test "show index-cache directory" $re_pre\[^\r\n\]*$re_post
>       }
>   }
>   
> @@ -69,7 +56,6 @@ with_test_prefix "all env vars" {
>   
>   	clean_restart
>   
> -	gdb_test "show index-cache directory" \
> -	    "The directory of the index cache is \"\"\\."
> +	gdb_test "show index-cache directory" $re_pre$re_post
>       }
>   }
> 
> base-commit: 5a655b5291b3f56088409d34e9077e98af63de60