3 files changed, 154 insertions, 19 deletions

diff --git a/dhall_syntax/src/core/import.rs b/dhall_syntax/src/core/import.rs
index c328e34..ea42dbc 100644
--- a/dhall_syntax/src/core/import.rs
+++ b/dhall_syntax/src/core/import.rs
@@ -11,10 +11,41 @@ pub enum FilePrefix {
     Home,
 }
 
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct Directory {
+    pub components: Vec<String>,
+}
+
+impl IntoIterator for Directory {
+    type Item = String;
+    type IntoIter = ::std::vec::IntoIter<Self::Item>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.components.into_iter()
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct File {
+    pub directory: Directory,
+    pub file: String,
+}
+
+impl IntoIterator for File {
+    type Item = String;
+    type IntoIter = ::std::vec::IntoIter<Self::Item>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        let mut paths = self.directory.components;
+        paths.push(self.file);
+        paths.into_iter()
+    }
+}
+
 /// The location of import (i.e. local vs. remote vs. environment)
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub enum ImportLocation {
-    Local(FilePrefix, Vec<String>),
+    Local(FilePrefix, File),
     Remote(URL),
     Env(String),
     Missing,
@@ -24,7 +55,7 @@ pub enum ImportLocation {
 pub struct URL {
     pub scheme: Scheme,
     pub authority: String,
-    pub path: Vec<String>,
+    pub path: File,
     pub query: Option<String>,
     pub headers: Option<Box<ImportHashed>>,
 }
@@ -59,3 +90,90 @@ pub struct Import {
     pub mode: ImportMode,
     pub location_hashed: ImportHashed,
 }
+
+pub trait Canonicalize {
+    fn canonicalize(&self) -> Self;
+}
+
+impl Canonicalize for Directory {
+    fn canonicalize(&self) -> Directory {
+        let mut components = Vec::new();
+        let mut dir_components = self.clone().into_iter();
+
+        loop {
+           let component = dir_components.next();
+           match component.as_ref() {
+               // ───────────────────
+               // canonicalize(ε) = ε
+               None => break,
+
+               // canonicalize(directory₀) = directory₁
+               // ───────────────────────────────────────
+               // canonicalize(directory₀/.) = directory₁
+               Some(c) if c == "." => continue,
+
+               Some(c) if c == ".." => match dir_components.next() {
+                   // canonicalize(directory₀) = ε
+                   // ────────────────────────────
+                   // canonicalize(directory₀/..) = /..
+                   None => components.push("..".to_string()),
+
+                   // canonicalize(directory₀) = directory₁/..
+                   // ──────────────────────────────────────────────
+                   // canonicalize(directory₀/..) = directory₁/../..
+                   Some(ref c) if c == ".." => {
+                       components.push("..".to_string());
+                       components.push("..".to_string());
+                   },
+
+                   // canonicalize(directory₀) = directory₁/component
+                   // ───────────────────────────────────────────────  ; If "component" is not
+                   // canonicalize(directory₀/..) = directory₁         ; ".."
+                   Some(_) => continue,
+               },
+
+               // canonicalize(directory₀) = directory₁
+               // ─────────────────────────────────────────────────────────  ; If no other
+               // canonicalize(directory₀/component) = directory₁/component  ; rule matches
+               Some(c) => components.push(c.clone()),
+           }
+        }
+
+        Directory { components: components }
+    }
+}
+
+impl Canonicalize for File {
+    fn canonicalize(&self) -> File {
+        File { directory: self.directory.canonicalize(), file: self.file.clone() }
+    }
+}
+
+impl Canonicalize for ImportLocation {
+    fn canonicalize(&self) -> ImportLocation {
+        match self {
+            ImportLocation::Local(prefix, file) => ImportLocation::Local(*prefix, file.canonicalize()),
+            ImportLocation::Remote(url) => ImportLocation::Remote(URL {
+                    scheme: url.scheme,
+                    authority: url.authority.clone(),
+                    path: url.path.canonicalize(),
+                    query: url.query.clone(),
+                    headers: url.headers.clone().map(|boxed_hash| Box::new(boxed_hash.canonicalize())),
+            }),
+            ImportLocation::Env(name) => ImportLocation::Env(name.to_string()),
+            ImportLocation::Missing => ImportLocation::Missing,
+        }
+    }
+}
+
+impl Canonicalize for ImportHashed {
+    fn canonicalize(&self) -> ImportHashed {
+        ImportHashed { hash: self.hash.clone(), location: self.location.canonicalize() }
+    }
+}
+
+impl Canonicalize for Import {
+    fn canonicalize(&self) -> Import {
+        Import { mode: self.mode, location_hashed: self.location_hashed.canonicalize() }
+    }
+}
diff --git a/dhall_syntax/src/parser.rs b/dhall_syntax/src/parser.rs
index 9d9a374..7675622 100644
--- a/dhall_syntax/src/parser.rs
+++ b/dhall_syntax/src/parser.rs
@@ -146,6 +146,14 @@ fn debug_pair(pair: Pair<Rule>) -> String {
     s
 }
 
+fn to_file(path: Vec<String>) -> Result<File, String> {
+    let mut path = path;
+    let file_name: Option<String> = path.pop();
+    let file = file_name.ok_or("Empty file path was provided")?;
+    let directory = Directory { components: path };
+    Ok(File { directory: directory, file: file })
+}
+
 macro_rules! make_parser {
     (@pattern, rule, $name:ident) => (Rule::$name);
     (@pattern, token_rule, $name:ident) => (Rule::$name);
@@ -589,19 +597,25 @@ make_parser! {
     });
 
     rule!(http_raw<URL>; children!(
-        [scheme(sch), authority(auth), path(p)] => URL {
-            scheme: sch,
-            authority: auth,
-            path: p,
-            query: None,
-            headers: None,
+        [scheme(sch), authority(auth), path(p)] => {
+            let file = to_file(p)?;
+            URL {
+                scheme: sch,
+                authority: auth,
+                path: file,
+                query: None,
+                headers: None,
+            }
         },
-        [scheme(sch), authority(auth), path(p), query(q)] => URL {
-            scheme: sch,
-            authority: auth,
-            path: p,
-            query: Some(q),
-            headers: None,
+        [scheme(sch), authority(auth), path(p), query(q)] => {
+            let file = to_file(p)?;
+            URL {
+                scheme: sch,
+                authority: auth,
+                path: file,
+                query: Some(q),
+                headers: None,
+            }
         },
     ));
 
@@ -655,7 +669,8 @@ make_parser! {
             ImportLocation::Remote(url)
         },
         [local((prefix, p))] => {
-            ImportLocation::Local(prefix, p)
+            let file = to_file(p)?;
+            ImportLocation::Local(prefix, file)
         },
     ));
 
diff --git a/dhall_syntax/src/printer.rs b/dhall_syntax/src/printer.rs
index dbed55d..8503a1e 100644
--- a/dhall_syntax/src/printer.rs
+++ b/dhall_syntax/src/printer.rs
@@ -380,17 +380,19 @@ impl Display for ImportHashed {
                     Absolute => "",
                 };
                 write!(f, "{}/", prefix)?;
-                let path: String = path
-                    .iter()
+                let full_path: String = path
+                    .clone()
+                    .into_iter()
                     .map(|c| fmt_local_path_component(c.as_ref()))
                     .join("/");
-                f.write_str(&path)?;
+                f.write_str(&full_path)?;
             }
             Remote(url) => {
                 write!(f, "{}://{}/", url.scheme, url.authority,)?;
                 let path: String = url
                     .path
-                    .iter()
+                    .clone()
+                    .into_iter()
                     .map(|c| fmt_remote_path_component(c.as_ref()))
                     .join("/");
                 f.write_str(&path)?;