feat(path): Existence predicate

Part of assert-rs#8.

Author: epage

src/predicate/mod.rs

@@ -24,6 +24,7 @@ pub use self::set::{contains, contains_hashable, contains_ord, ContainsPredicate
 
 // specialized primitive `Predicate` types
 pub mod str;
+pub mod path;
 
 // combinators
 mod boolean;

src/predicate/path/existence.rs

@@ -0,0 +1,57 @@
+// Copyright (c) 2018 The predicates-rs Project Developers.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::path;
+
+use Predicate;
+
+/// Predicate that checks if a file is present
+///
+/// This is created by the `predicate::path::exists` and `predicate::path::missing`.
+#[derive(Debug)]
+pub struct ExistencePredicate {
+    exists: bool,
+}
+
+impl Predicate for ExistencePredicate {
+    type Item = path::Path;
+
+    fn eval(&self, path: &path::Path) -> bool {
+        path.exists() == self.exists
+    }
+}
+
+/// Creates a new `Predicate` that ensures the path exists.
+///
+/// # Examples
+///
+/// ```
+/// use std::path::Path;
+/// use predicates::predicate::*;
+///
+/// let predicate_fn = path::exists();
+/// assert_eq!(true, predicate_fn.eval(Path::new("Cargo.toml")));
+/// ```
+pub fn exists() -> ExistencePredicate {
+    ExistencePredicate { exists: true }
+}
+
+/// Creates a new `Predicate` that ensures the path doesn't exist.
+///
+/// # Examples
+///
+/// ```
+/// use std::path::Path;
+/// use predicates::predicate::*;
+///
+/// let predicate_fn = path::missing();
+/// assert_eq!(true, predicate_fn.eval(Path::new("non-existent-file.foo")));
+/// ```
+pub fn missing() -> ExistencePredicate {
+    ExistencePredicate { exists: false }
+}

src/predicate/path/mod.rs

@@ -0,0 +1,14 @@
+// Copyright (c) 2018 The predicates-rs Project Developers.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Path Predicates
+//!
+//! This module contains predicates specifiuc to the file system.
+
+mod existence;
+pub use self::existence::{exists, missing, ExistencePredicate};