Move transpose to util module

src/app.rs

@@ -20,6 +20,7 @@ use errors::*;
 use inputfile::InputFile;
 use line_range::LineRange;
 use style::{OutputComponent, OutputComponents, OutputWrap};
+use util::transpose;
 
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub enum PagingMode {
@@ -74,12 +75,6 @@ fn is_truecolor_terminal() -> bool {
         .unwrap_or(false)
 }
 
-/// Helper function that might appear in Rust stable at some point
-/// (https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.transpose)
-fn transpose<T>(opt: Option<Result<T>>) -> Result<Option<T>> {
-    opt.map_or(Ok(None), |res| res.map(Some))
-}
-
 pub struct App {
     pub matches: ArgMatches<'static>,
     interactive_output: bool,

src/main.rs

@@ -36,6 +36,7 @@ mod preprocessor;
 mod printer;
 mod style;
 mod terminal;
+mod util;
 
 use std::collections::HashSet;
 use std::io;

src/util.rs

@@ -0,0 +1,27 @@
+/// Helper function that might appear in Rust stable at some point
+/// (https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.transpose)
+pub fn transpose<T, E>(opt: Option<Result<T, E>>) -> Result<Option<T>, E> {
+    opt.map_or(Ok(None), |res| res.map(Some))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::transpose;
+
+    #[derive(Debug, PartialEq)]
+    struct TestError;
+
+    type TestResult<T> = Result<T, TestError>;
+
+    #[test]
+    fn basic() {
+        let a: Option<TestResult<i32>> = Some(Ok(2));
+        assert_eq!(Ok(Some(2)), transpose(a));
+
+        let b: Option<TestResult<i32>> = Some(Err(TestError));
+        assert_eq!(Err(TestError), transpose(b));
+
+        let c: Option<TestResult<i32>> = None;
+        assert_eq!(Ok(None), transpose(c));
+    }
+}