Normalize paths in Windows (fix #113) (#116)

While `//?/C:/Users/Someone/config-files` is a valid path, it's not very human friendly.
Such paths are returned from `BaseDirs`. This patch formats them in the traditional way.

src/utils.rs

@@ -1,8 +1,8 @@
 use super::error::{Error, ErrorKind};
 use log::{debug, error};
 use std::ffi::OsStr;
-use std::fmt::Debug;
-use std::path::{Path, PathBuf};
+use std::fmt::{self, Debug};
+use std::path::{Component, Path, PathBuf};
 use std::process::{ExitStatus, Output};
 use which_crate;
 
@@ -68,3 +68,86 @@ pub fn which<T: AsRef<OsStr> + Debug>(binary_name: T) -> Option<PathBuf> {
         }
     }
 }
+
+/// `std::fmt::Display` implementation for `std::path::Path`.
+///
+/// This struct differs from `std::path::Display` in that in Windows it takes care of printing backslashes
+/// instead of slashes and don't print the `\\?` prefix in long paths.
+pub struct HumanizedPath<'a> {
+    path: &'a Path,
+}
+
+impl<'a> From<&'a Path> for HumanizedPath<'a> {
+    fn from(path: &'a Path) -> Self {
+        Self { path }
+    }
+}
+
+impl<'a> fmt::Display for HumanizedPath<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if cfg!(windows) {
+            let mut iterator = self.path.components().peekable();
+
+            while let Some(component) = iterator.next() {
+                let mut print_seperator = iterator.peek().is_some();
+
+                match &component {
+                    Component::Normal(c) if *c == "?" => {
+                        print_seperator = false;
+                    }
+                    Component::RootDir | Component::CurDir => {
+                        print_seperator = false;
+                    }
+                    Component::ParentDir => {
+                        write!(f, "..")?;
+                    }
+                    Component::Prefix(p) => {
+                        write!(f, "{}", p.as_os_str().to_string_lossy())?;
+                        print_seperator = true;
+                    }
+                    Component::Normal(c) => {
+                        write!(f, "{}", c.to_string_lossy())?;
+                    }
+                };
+
+                if print_seperator {
+                    write!(f, "{}", std::path::MAIN_SEPARATOR)?;
+                }
+            }
+        } else {
+            write!(f, "{}", self.path.display())?;
+        }
+
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+#[cfg(windows)]
+mod tests {
+    use super::*;
+
+    fn humanize<P: AsRef<Path>>(path: P) -> String {
+        format!("{}", HumanizedPath::from(path.as_ref()))
+    }
+
+    #[test]
+    fn test_just_drive() {
+        assert_eq!("C:\\", humanize("C:\\"));
+    }
+
+    #[test]
+    fn test_path() {
+        assert_eq!("C:\\hi", humanize("C:\\hi"));
+    }
+
+    #[test]
+    fn test_unc() {
+        assert_eq!("\\\\server\\share\\", humanize("\\\\server\\share"));
+    }
+
+    #[test]
+    fn test_long_path() {
+        assert_eq!("C:\\hi", humanize("//?/C:/hi"));
+    }
+}