From c3033ca75f7218dd078b5bd0e84e2d7c7414c2dc Mon Sep 17 00:00:00 2001
From: Alex Burka <alex@alexburka.com>
Date: Fri, 27 Oct 2017 12:54:41 -0400
Subject: [PATCH 1/2] imp: make Arg::validator more flexible

Makes the validator functions more flexible by changing the return
type from Result<(), String> to Result<O, E> where O is anything
and E is anything convertible to a String.

This allows, for example, using the same function for validating
and parsing your argument.

Breaking change (albeit tiny) due to function signature change.
---
 src/args/arg.rs | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/src/args/arg.rs b/src/args/arg.rs
index 824c862b574..d827826fdbb 100644
--- a/src/args/arg.rs
+++ b/src/args/arg.rs
@@ -1830,11 +1830,11 @@ impl<'a, 'b> Arg<'a, 'b> {
     /// [`Result`]: https://doc.rust-lang.org/std/result/enum.Result.html
     /// [`Err(String)`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Err
     /// [`Rc`]: https://doc.rust-lang.org/std/rc/struct.Rc.html
-    pub fn validator<F>(mut self, f: F) -> Self
-    where
-        F: Fn(String) -> Result<(), String> + 'static,
+    pub fn validator<F, O, E>(mut self, f: F) -> Self
+        where F: Fn(String) -> Result<O, E> + 'static,
+              E: ToString
     {
-        self.validator = Some(Rc::new(f));
+        self.validator = Some(Rc::new(move |s| f(s).map(|_| ()).map_err(|e| e.to_string())));
         self
     }
 
@@ -1868,11 +1868,10 @@ impl<'a, 'b> Arg<'a, 'b> {
     /// [`Result`]: https://doc.rust-lang.org/std/result/enum.Result.html
     /// [`Err(String)`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Err
     /// [`Rc`]: https://doc.rust-lang.org/std/rc/struct.Rc.html
-    pub fn validator_os<F>(mut self, f: F) -> Self
-    where
-        F: Fn(&OsStr) -> Result<(), OsString> + 'static,
+    pub fn validator_os<F, O>(mut self, f: F) -> Self
+        where F: Fn(&OsStr) -> Result<O, OsString> + 'static
     {
-        self.validator_os = Some(Rc::new(f));
+        self.validator_os = Some(Rc::new(move |s| f(s).map(|_| ())));
         self
     }
 

From c5d79d854e50142e24881f098160a8290e017fd9 Mon Sep 17 00:00:00 2001
From: Alex Burka <aburka@seas.upenn.edu>
Date: Wed, 4 Apr 2018 20:45:22 -0400
Subject: [PATCH 2/2] test validator with custom return type

---
 tests/env.rs | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tests/env.rs b/tests/env.rs
index aded47bd8ca..431a0211734 100644
--- a/tests/env.rs
+++ b/tests/env.rs
@@ -240,6 +240,21 @@ fn validator() {
     assert_eq!(m.value_of("arg").unwrap(), "env");
 }
 
+#[test]
+fn validator_output() {
+    env::set_var("CLP_TEST_ENV", "42");
+
+    let r = App::new("df")
+        .arg(
+            Arg::from_usage("[arg] 'some opt'")
+                .env("CLP_TEST_ENV")
+                .validator(|s| s.parse::<i32>())
+        )
+        .get_matches_from_safe(vec![""]);
+
+    assert_eq!(r.unwrap().value_of("arg").unwrap().parse(), Ok(42));
+}
+
 #[test]
 fn validator_invalid() {
     env::set_var("CLP_TEST_ENV", "env");