Add @use member usage and load error tests

spec/core_functions/function_exists.hrx

@@ -0,0 +1,201 @@
+<===> global/input.scss
+@function global-function() {@return null}
+
+a {b: function-exists(global-function)}
+
+<===> global/output.css
+a {
+  b: true;
+}
+
+<===>
+================================================================================
+<===> local/options.yml
+---
+:todo:
+- libsass # sass/libsass#2831
+
+<===> local/input.scss
+a {
+  @function local-function() {@return null}
+  b: function-exists(local-function);
+}
+
+<===> local/output.css
+a {
+  b: true;
+}
+
+<===>
+================================================================================
+<===> dash_insensitive/input.scss
+@function global-function() {@return null}
+
+a {b: function-exists(global_function)}
+
+<===> dash_insensitive/output.css
+a {
+  b: true;
+}
+
+<===>
+================================================================================
+<===> through_import/input.scss
+@import "other";
+a {b: function-exists(global-function)}
+
+<===> through_import/other.scss
+@function global-function() {@return null}
+
+<===> through_import/output.css
+a {
+  b: true;
+}
+
+<===>
+================================================================================
+<===> through_use/options.yml
+---
+:todo:
+- libsass # sass/libsass#2807
+:ignore_for:
+- ruby-sass
+
+<===> through_use/input.scss
+@use "other" as *;
+a {b: function-exists(global-function)}
+
+<===> through_use/other.scss
+@function global-function() {@return null}
+
+<===> through_use/output.css
+a {
+  b: true;
+}
+
+<===>
+================================================================================
+<===> non_existent/input.scss
+a {
+  b: function-exists(non-existent);
+}
+
+<===> non_existent/output.css
+a {
+  b: false;
+}
+
+<===>
+================================================================================
+<===> keyword/input.scss
+a {b: function-exists($name: foo)}
+
+<===> keyword/output.css
+a {
+  b: false;
+}
+
+<===>
+================================================================================
+<===> error/argument/type/input.scss
+a {b: function-exists(12px)}
+
+<===> error/argument/type/error
+Error: $name: 12px is not a string.
+  ,
+1 | a {b: function-exists(12px)}
+  |       ^^^^^^^^^^^^^^^^^^^^^
+  '
+  /sass/spec/core_functions/function_exists/error/argument/type/input.scss 1:7  root stylesheet
+
+<===> error/argument/type/error-ruby-sass
+Error: $name: 12px is not a string for `function-exists'
+        on line 1 of /sass/spec/core_functions/function_exists/error/argument/type/input.scss
+  Use --trace for backtrace.
+
+<===> error/argument/type/error-libsass
+Error: $name: 12px is not a string for `function-exists'
+        on line 1:7 of /sass/spec/core_functions/function_exists/error/argument/type/input.scss, in function `function-exists`
+        from line 1:7 of /sass/spec/core_functions/function_exists/error/argument/type/input.scss
+>> a {b: function-exists(12px)}
+
+   ------^
+
+<===>
+================================================================================
+<===> error/argument/too_few/input.scss
+a {b: function-exists()}
+
+<===> error/argument/too_few/error
+Error: Missing argument $name.
+  ,
+1 | a {b: function-exists()}
+  |       ^^^^^^^^^^^^^^^^^
+  '
+  /sass/spec/core_functions/function_exists/error/argument/too_few/input.scss 1:7  root stylesheet
+
+<===> error/argument/too_few/error-ruby-sass
+Error: wrong number of arguments (0 for 1) for `function-exists'
+        on line 1 of /sass/spec/core_functions/function_exists/error/argument/too_few/input.scss
+  Use --trace for backtrace.
+
+<===> error/argument/too_few/error-libsass
+Error: Function function-exists is missing argument $name.
+        on line 1 of /sass/spec/core_functions/function_exists/error/argument/too_few/input.scss
+>> a {b: function-exists()}
+
+   ------^
+
+<===>
+================================================================================
+<===> error/argument/too_many/input.scss
+a {b: function-exists(foo, bar)}
+
+<===> error/argument/too_many/error
+Error: Only 1 argument allowed, but 2 were passed.
+  ,
+1 | a {b: function-exists(foo, bar)}
+  |       ^^^^^^^^^^^^^^^^^^^^^^^^^
+  '
+  /sass/spec/core_functions/function_exists/error/argument/too_many/input.scss 1:7  root stylesheet
+
+<===> error/argument/too_many/error-ruby-sass
+Error: wrong number of arguments (2 for 1) for `function-exists'
+        on line 1 of /sass/spec/core_functions/function_exists/error/argument/too_many/input.scss
+  Use --trace for backtrace.
+
+<===> error/argument/too_many/error-libsass
+Error: wrong number of arguments (2 for 1) for `function-exists'
+        on line 1:7 of /sass/spec/core_functions/function_exists/error/argument/too_many/input.scss
+>> a {b: function-exists(foo, bar)}
+
+   ------^
+
+<===>
+================================================================================
+<===> conflict/options.yml
+---
+:todo:
+- libsass # sass/libsass#2807
+:ignore_for:
+- ruby-sass
+
+<===> conflict/input.scss
+@use "other1" as *;
+@use "other2" as *;
+
+a {b: function-exists(member)}
+
+<===> conflict/other1.scss
+@function member() {@return from other1}
+
+<===> conflict/other2.scss
+@function member() {@return from other2}
+
+<===> conflict/error
+Error: Multiple global modules have a function named "member".
+  ,
+4 | a {b: function-exists(member)}
+  |       ^^^^^^^^^^^^^^^^^^^^^^^
+  '
+  /sass/spec/core_functions/function_exists/conflict/input.scss 4:7  root stylesheet