Add path_exists() function (#1106)

README.md

@@ -981,6 +981,10 @@ These functions can fail, for example if a path does not have an extension, whic
 
 - `clean(path)` - Simplify `path` by removing extra path separators, intermediate `.` components, and `..` where possible. `clean("foo//bar")` is `foo/bar`, `clean("foo/..")` is `.`, `clean("foo/./bar")` is `foo/bar`.
 
+#### Filesystem Access
+
+- `path_exists(path)` - Returns `true` if the path points at an existing entity and `false` otherwise. Traverses symbolic links, and returns `false` if the path is inaccessible or points to a broken symlink.
+
 ### Command Evaluation Using Backticks
 
 Backticks can be used to store the result of commands:

src/function.rs

@@ -30,6 +30,7 @@ lazy_static! {
     ("os", Nullary(os)),
     ("os_family", Nullary(os_family)),
     ("parent_directory", Unary(parent_directory)),
+    ("path_exists", Unary(path_exists)),
     ("quote", Unary(quote)),
     ("replace", Ternary(replace)),
     ("trim", Unary(trim)),
@@ -210,6 +211,10 @@ fn parent_directory(_context: &FunctionContext, path: &str) -> Result<String, St
     .ok_or_else(|| format!("Could not extract parent directory from `{}`", path))
 }
 
+fn path_exists(_context: &FunctionContext, path: &str) -> Result<String, String> {
+  Ok(Utf8Path::new(path).exists().to_string())
+}
+
 fn quote(_context: &FunctionContext, s: &str) -> Result<String, String> {
   Ok(format!("'{}'", s.replace('\'', "'\\''")))
 }

tests/functions.rs

@@ -382,3 +382,24 @@ fn join_argument_count_error() {
     .status(EXIT_FAILURE)
     .run();
 }
+
+#[test]
+fn test_path_exists_filepath_exist() {
+  Test::new()
+    .tree(tree! {
+      testfile: ""
+    })
+    .justfile("x := path_exists('testfile')")
+    .args(&["--evaluate", "x"])
+    .stdout("true")
+    .run();
+}
+
+#[test]
+fn test_path_exists_filepath_doesnt_exist() {
+  Test::new()
+    .justfile("x := path_exists('testfile')")
+    .args(&["--evaluate", "x"])
+    .stdout("false")
+    .run();
+}