Add source_file() and source_directory()

syntax/just.vim

@@ -229,7 +229,7 @@ syn match justFunctionCall "\v\w+%(\s|\\\n)*\(@=" transparent contains=justBuilt
 
 " error() is intentionally not included in this list
 syn keyword justBuiltInFunction
-   \ absolute_path append arch blake3 blake3_file cache_directory canonicalize capitalize choose clean config_directory config_local_directory data_directory data_local_directory encode_uri_component env env_var env_var_or_default executable_directory extension file_name file_stem home_directory invocation_directory invocation_directory_native join just_executable justfile justfile_directory just_pid kebabcase lowercamelcase lowercase num_cpus os os_family parent_directory path_exists prepend quote replace replace_regex semver_matches sha256 sha256_file shell shoutykebabcase shoutysnakecase snakecase titlecase trim trim_end trim_end_match trim_end_matches trim_start trim_start_match trim_start_matches uppercamelcase uppercase uuid without_extension
+   \ absolute_path append arch blake3 blake3_file cache_directory canonicalize capitalize choose clean config_directory config_local_directory data_directory data_local_directory encode_uri_component env env_var env_var_or_default executable_directory extension file_name file_stem home_directory invocation_directory invocation_directory_native join just_executable justfile justfile_directory just_pid kebabcase lowercamelcase lowercase num_cpus os os_family parent_directory path_exists prepend quote replace replace_regex semver_matches sha256 sha256_file shell shoutykebabcase shoutysnakecase snakecase source_directory source_file titlecase trim trim_end trim_end_match trim_end_matches trim_start trim_start_match trim_start_matches uppercamelcase uppercase uuid without_extension
    \ contained
 
 syn match justUserDefinedError "\v%(assert|error)%(%(\s|\\\n)*\()@="

tests/cases/expressions.html

@@ -33,3 +33,5 @@
 _true <span class="Operator">:=</span> <span class="Exception">assert</span>(<span class="String">'1'</span> <span class="Operator">!=</span> <span class="String">'0'</span>, <span class="String">'1 is not 0'</span>)
 
 shell_command <span class="Operator">:=</span> <span class="Function">shell</span>(<span class="String">'echo "$@"'</span>, _true, random1)
+
+this_source <span class="Operator">:=</span> <span class="Function">source_directory</span>() <span class="Operator">+</span> <span class="String">"</span><span class="Special">\n</span><span class="String"> -&gt; "</span> <span class="Operator">+</span> <span class="Function">source_file</span>()

tests/cases/expressions.just

@@ -33,3 +33,5 @@ shell_expanded5 := x'''
 _true := assert('1' != '0', '1 is not 0')
 
 shell_command := shell('echo "$@"', _true, random1)
+
+this_source := source_directory() + "\n -> " + source_file()