Untangle caching code

11 files changed, 156 insertions, 662 deletions

diff --git a/dhall/src/lib.rs b/dhall/src/lib.rs
index 87c461b..f9d259c 100644
--- a/dhall/src/lib.rs
+++ b/dhall/src/lib.rs
@@ -13,6 +13,7 @@ pub mod error;
 pub mod operations;
 pub mod semantics;
 pub mod syntax;
+pub mod utils;
 
 use std::fmt::Display;
 use std::path::Path;
@@ -37,8 +38,8 @@ pub struct Resolved(Hir);
 /// A typed expression
 #[derive(Debug, Clone)]
 pub struct Typed {
-    hir: Hir,
-    ty: Type,
+    pub hir: Hir,
+    pub ty: Type,
 }
 
 /// A normalized expression.
diff --git a/dhall/src/semantics/parse.rs b/dhall/src/semantics/parse.rs
index 82396e0..a770c15 100644
--- a/dhall/src/semantics/parse.rs
+++ b/dhall/src/semantics/parse.rs
@@ -1,5 +1,3 @@
-use std::fs::File;
-use std::io::Read;
 use std::path::Path;
 use url::Url;
 
@@ -36,9 +34,8 @@ pub fn parse_binary(data: &[u8]) -> Result<Parsed, Error> {
 }
 
 pub fn parse_binary_file(f: &Path) -> Result<Parsed, Error> {
-    let mut buffer = Vec::new();
-    File::open(f)?.read_to_end(&mut buffer)?;
-    let expr = binary::decode(&buffer)?;
+    let data = crate::utils::read_binary_file(f)?;
+    let expr = binary::decode(&data)?;
     let root = ImportLocation::Local(f.to_owned());
     Ok(Parsed(expr, root))
 }
diff --git a/dhall/src/semantics/resolve/cache.rs b/dhall/src/semantics/resolve/cache.rs
index dd686ea..2abe7a9 100644
--- a/dhall/src/semantics/resolve/cache.rs
+++ b/dhall/src/semantics/resolve/cache.rs
@@ -2,13 +2,10 @@ use std::env;
 use std::io::Write;
 use std::path::{Path, PathBuf};
 
-use crate::error::{CacheError, Error, ErrorKind};
-use crate::parse::parse_binary_file;
-use crate::semantics::{Import, TypedHir};
-use crate::syntax::Hash;
-use crate::syntax::{binary, Expr};
-use crate::Parsed;
-use std::env::VarError;
+use crate::error::{CacheError, Error};
+use crate::parse::parse_binary;
+use crate::semantics::TypedHir;
+use crate::syntax::{binary, Hash};
 use std::ffi::OsStr;
 use std::fs::File;
 
@@ -20,634 +17,99 @@ const ALTERNATE_CACHE_ENV_VAR: &str = "HOME";
 const ALTERNATE_CACHE_ENV_VAR: &str = "LOCALAPPDATA";
 
 #[cfg(any(unix, windows))]
-fn load_cache_dir(
-    env_provider: impl Fn(&str) -> Result<String, VarError> + Copy,
-) -> Result<PathBuf, CacheError> {
-    let env_provider = |s| {
-        env_provider(s)
-            .map(PathBuf::from)
-            .map_err(|_| CacheError::MissingConfiguration)
+fn default_cache_dir() -> Result<PathBuf, CacheError> {
+    let cache_base_path = match env::var(OsStr::new(CACHE_ENV_VAR)) {
+        Ok(path) => PathBuf::from(path),
+        Err(_) => match env::var(OsStr::new(ALTERNATE_CACHE_ENV_VAR)) {
+            Ok(path) => PathBuf::from(path).join(".cache"),
+            Err(_) => return Err(CacheError::MissingConfiguration),
+        },
     };
-    let cache_base_path = env_provider(CACHE_ENV_VAR).or_else(|_| {
-        env_provider(ALTERNATE_CACHE_ENV_VAR).map(|path| path.join(".cache"))
-    })?;
     Ok(cache_base_path.join("dhall"))
 }
+
 #[cfg(not(any(unix, windows)))]
-fn load_cache_dir(
-    _provider: impl Fn(&str) -> Result<String, VarError> + Copy,
-) -> Result<PathBuf, CacheError> {
+fn default_cache_dir() -> Result<PathBuf, CacheError> {
     Err(CacheError::MissingConfiguration)
 }
 
 #[derive(Debug, Clone, PartialEq)]
 pub struct Cache {
-    cache_dir: Option<PathBuf>,
+    cache_dir: PathBuf,
 }
 
 impl Cache {
-    fn new_with_provider(
-        provider: impl Fn(&str) -> Result<String, VarError> + Copy,
-    ) -> Cache {
-        // Should warn that we can't initialize cache on error
-        let cache_dir = load_cache_dir(provider).and_then(|path| {
-            if !path.exists() {
-                std::fs::create_dir_all(path.as_path())
-                    .map(|_| path)
-                    .map_err(|e| CacheError::InitialisationError { cause: e })
-            } else {
-                Ok(path)
-            }
-        });
-        Cache {
-            cache_dir: cache_dir.ok(),
+    pub fn new() -> Result<Cache, Error> {
+        let cache_dir = default_cache_dir()?;
+        if !cache_dir.exists() {
+            std::fs::create_dir_all(&cache_dir)
+                .map_err(|e| CacheError::InitialisationError { cause: e })?;
         }
+        Ok(Cache { cache_dir })
     }
 
-    pub fn new() -> Cache {
-        Cache::new_with_provider(|name| env::var(OsStr::new(name)))
-    }
-}
-
-impl Cache {
-    fn cache_file(&self, import: &Import) -> Option<PathBuf> {
-        self.cache_dir
-            .as_ref()
-            .and_then(|cache_dir| {
-                import.hash.as_ref().map(|hash| (cache_dir, hash))
-            })
-            .map(|(cache_dir, hash)| cache_dir.join(cache_filename(hash)))
+    fn entry_path(&self, hash: &Hash) -> PathBuf {
+        self.cache_dir.join(filename_for_hash(hash))
     }
 
-    fn search_cache_file(&self, import: &Import) -> Option<PathBuf> {
-        self.cache_file(import)
-            .filter(|cache_file| cache_file.exists())
+    pub fn get(&self, hash: &Hash) -> Result<TypedHir, Error> {
+        let path = self.entry_path(hash);
+        let res = read_cache_file(&path, hash);
+        if let Err(_) = res {
+            if path.exists() {
+                // Delete cache file since it's invalid. We ignore the error.
+                let _ = std::fs::remove_file(&path);
+            }
+        }
+        res
     }
 
-    fn search_cache(&self, import: &Import) -> Option<Result<Parsed, Error>> {
-        self.search_cache_file(import)
-            .map(|cache_file| parse_binary_file(cache_file.as_path()))
+    pub fn insert(&self, hash: &Hash, expr: &TypedHir) -> Result<(), Error> {
+        let path = self.entry_path(hash);
+        write_cache_file(&path, expr)
     }
+}
 
-    // Side effect since we don't use the result
-    fn delete_cache(&self, import: &Import) {
-        self.search_cache_file(import)
-            .map(|cache_file| std::fs::remove_file(cache_file.as_path()));
-    }
+/// Read a file from the cache, also checking that its hash is valid.
+fn read_cache_file(path: &Path, hash: &Hash) -> Result<TypedHir, Error> {
+    let data = crate::utils::read_binary_file(path)?;
 
-    // Side effect since we don't use the result
-    fn save_expr(&self, import: &Import, expr: &Expr) {
-        self.cache_file(import)
-            .map(|cache_file| save_expr(cache_file.as_path(), expr));
+    match hash {
+        Hash::SHA256(hash) => {
+            let actual_hash = crate::utils::sha256_hash(&data);
+            if hash[..] != actual_hash[..] {
+                return Err(CacheError::CacheHashInvalid.into());
+            }
+        }
     }
 
-    pub fn caching_import<F, R>(
-        &self,
-        import: &Import,
-        fetcher: F,
-        mut resolver: R,
-    ) -> Result<TypedHir, Error>
-    where
-        F: FnOnce() -> Result<Parsed, Error>,
-        R: FnMut(Parsed) -> Result<TypedHir, Error>,
-    {
-        // Lookup the cache
-        self.search_cache(import)
-            // On cache found
-            .and_then(|cache_result| {
-                // Try to resolve the cache imported content
-                match cache_result.and_then(|parsed| resolver(parsed)).and_then(
-                    |typed_hir| {
-                        check_hash(import.hash.as_ref().unwrap(), typed_hir)
-                    },
-                ) {
-                    // Cache content is invalid (can't be parsed / can't be resolved / content sha invalid )
-                    Err(_) => {
-                        // Delete cache file since it's invalid
-                        self.delete_cache(import);
-                        // Result as there were no cache
-                        None
-                    }
-                    // Cache valid
-                    r => Some(r),
-                }
-            })
-            .unwrap_or_else(|| {
-                // Fetch and resolve as provided
-                let imported = fetcher().and_then(resolver);
-                // Save in cache the result if ok
-                let _ = imported.as_ref().map(|(hir, _)| {
-                    self.save_expr(import, &hir.to_expr_noopts())
-                });
-                imported
-            })
-    }
+    let crate::Typed { hir, ty } =
+        parse_binary(&data)?.skip_resolve()?.typecheck()?;
+    Ok((hir, ty))
 }
 
-fn save_expr(file_path: &Path, expr: &Expr) -> Result<(), Error> {
-    File::create(file_path)?.write_all(binary::encode(expr)?.as_slice())?;
+/// Write a file to the cache.
+fn write_cache_file(path: &Path, expr: &TypedHir) -> Result<(), Error> {
+    let data = binary::encode(&expr.0.to_expr_noopts())?;
+    File::create(path)?.write_all(data.as_slice())?;
     Ok(())
 }
 
-fn check_hash(hash: &Hash, typed_hir: TypedHir) -> Result<TypedHir, Error> {
-    if hash.as_ref()[..] != typed_hir.0.to_expr_alpha().hash()?[..] {
-        Err(Error::new(ErrorKind::Cache(CacheError::CacheHashInvalid)))
-    } else {
-        Ok(typed_hir)
-    }
-}
-
-fn cache_filename<A: AsRef<[u8]>>(v: A) -> String {
-    format!("1220{}", hex::encode(v.as_ref()))
-}
-
-impl AsRef<[u8]> for Hash {
-    fn as_ref(&self) -> &[u8] {
-        match self {
-            Hash::SHA256(sha) => sha.as_slice(),
-        }
+fn filename_for_hash(hash: &Hash) -> String {
+    match hash {
+        Hash::SHA256(sha) => format!("1220{}", hex::encode(&sha)),
     }
 }
 
 #[cfg(test)]
 mod test {
     use super::*;
-    use crate::semantics::parse::parse_str;
-    use crate::syntax::{
-        parse_expr, ExprKind, ImportMode, ImportTarget, NumKind, Span,
-    };
-    use rand::distributions::Alphanumeric;
-    use rand::Rng;
-    use std::env::temp_dir;
-
-    #[cfg(any(unix, windows))]
-    #[test]
-    fn load_cache_dir_should_result_xdg_cache_first() {
-        let actual = load_cache_dir(|var| match var {
-            CACHE_ENV_VAR => Ok("/home/user/custom".to_string()),
-            _ => Err(VarError::NotPresent),
-        });
-        assert_eq!(actual.unwrap(), PathBuf::from("/home/user/custom/dhall"));
-    }
-
-    #[cfg(unix)]
-    #[test]
-    fn load_cache_dir_should_result_alternate() {
-        let actual = load_cache_dir(|var| match var {
-            ALTERNATE_CACHE_ENV_VAR => Ok("/home/user".to_string()),
-            _ => Err(VarError::NotPresent),
-        });
-        assert_eq!(actual.unwrap(), PathBuf::from("/home/user/.cache/dhall"));
-    }
-
-    #[test]
-    fn load_cache_dir_should_result_none() {
-        let actual = load_cache_dir(|_| Err(VarError::NotPresent));
-        assert!(matches!(
-            actual.unwrap_err(),
-            CacheError::MissingConfiguration
-        ));
-    }
-
-    #[test]
-    fn new_with_provider_should_create_cache_folder() {
-        let test_id = rand::thread_rng()
-            .sample_iter(Alphanumeric)
-            .take(36)
-            .collect::<String>();
-        let dir = temp_dir().join(test_id);
-
-        std::fs::create_dir_all(dir.as_path()).unwrap();
-
-        let actual = Cache::new_with_provider(|_| {
-            Ok(dir.clone().to_str().map(String::from).unwrap())
-        });
-        assert_eq!(
-            actual,
-            Cache {
-                cache_dir: Some(dir.join("dhall"))
-            }
-        );
-        assert!(dir.join("dhall").exists());
-        std::fs::remove_dir_all(dir.as_path()).unwrap();
-    }
-
-    #[test]
-    fn new_with_provider_should_return_cache_for_existing_folder() {
-        let test_id = rand::thread_rng()
-            .sample_iter(Alphanumeric)
-            .take(36)
-            .collect::<String>();
-        let dir = temp_dir().join(test_id);
-
-        std::fs::create_dir_all(dir.as_path()).unwrap();
-        File::create(dir.join("dhall")).unwrap();
-
-        assert!(dir.join("dhall").exists());
-
-        let actual = Cache::new_with_provider(|_| {
-            Ok(dir.clone().to_str().map(String::from).unwrap())
-        });
-        assert_eq!(
-            actual,
-            Cache {
-                cache_dir: Some(dir.join("dhall"))
-            }
-        );
-        std::fs::remove_dir_all(dir.as_path()).unwrap();
-    }
-
-    #[test]
-    fn caching_import_should_load_cache() -> Result<(), Error> {
-        let test_id = rand::thread_rng()
-            .sample_iter(Alphanumeric)
-            .take(36)
-            .collect::<String>();
-        let dir = temp_dir().join(test_id);
-
-        std::fs::create_dir_all(dir.as_path())?;
-
-        let cache = Cache::new_with_provider(|_| {
-            Ok(dir.clone().to_str().map(String::from).unwrap())
-        });
-
-        // Create cache file
-        let expr =
-            Expr::new(ExprKind::Num(NumKind::Natural(1)), Span::Artificial);
-        File::create(dir.join("dhall").join("1220d60d8415e36e86dae7f42933d3b0c4fe3ca238f057fba206c7e9fbf5d784fe15"))?
-            .write_all(binary::encode(&expr)?.as_ref())?;
-
-        let import = Import {
-            mode: ImportMode::Code,
-            location: ImportTarget::Missing,
-            hash: Some(Hash::SHA256(hex::decode("d60d8415e36e86dae7f42933d3b0c4fe3ca238f057fba206c7e9fbf5d784fe15").unwrap())),
-        };
-
-        let mut resolve_counter = 0;
-
-        let result = cache.caching_import(
-            &import,
-            || panic!("Should not fetch import"),
-            |parsed| {
-                resolve_counter += 1;
-                let result = parsed.resolve()?.typecheck()?;
-                Ok((result.normalize().to_hir(), result.ty))
-            },
-        );
-
-        assert!(result.is_ok());
-        assert_eq!(resolve_counter, 1);
-
-        std::fs::remove_dir_all(dir.as_path()).unwrap();
-        Ok(())
-    }
-
-    #[test]
-    fn caching_import_should_skip_cache_if_missing_cache_folder(
-    ) -> Result<(), Error> {
-        let cache = Cache::new_with_provider(|_| Err(VarError::NotPresent));
-
-        let import = Import {
-            mode: ImportMode::Code,
-            location: ImportTarget::Missing,
-            hash: Some(Hash::SHA256(hex::decode("d60d8415e36e86dae7f42933d3b0c4fe3ca238f057fba206c7e9fbf5d784fe15").unwrap())),
-        };
-
-        let mut resolve_counter = 0;
-        let mut fetcher_counter = 0;
-
-        let result = cache.caching_import(
-            &import,
-            || {
-                fetcher_counter += 1;
-                parse_str("1")
-            },
-            |parsed| {
-                resolve_counter += 1;
-                let result = parsed.resolve()?.typecheck()?;
-                Ok((result.normalize().to_hir(), result.ty))
-            },
-        );
-
-        assert!(result.is_ok(), "caching_import Should be valid");
-        assert_eq!(resolve_counter, 1);
-        assert_eq!(fetcher_counter, 1);
-        Ok(())
-    }
-
-    #[test]
-    fn caching_import_should_skip_cache_on_no_hash_import() -> Result<(), Error>
-    {
-        let cache = Cache::new_with_provider(|_| Err(VarError::NotPresent));
-
-        let import = Import {
-            mode: ImportMode::Code,
-            location: ImportTarget::Missing,
-            hash: None,
-        };
-
-        let mut resolve_counter = 0;
-        let mut fetcher_counter = 0;
-
-        let result = cache.caching_import(
-            &import,
-            || {
-                fetcher_counter += 1;
-                parse_str("1")
-            },
-            |parsed| {
-                resolve_counter += 1;
-                let result = parsed.resolve()?.typecheck()?;
-                Ok((result.normalize().to_hir(), result.ty))
-            },
-        );
-
-        assert!(result.is_ok(), "caching_import Should be valid");
-        assert_eq!(resolve_counter, 1);
-        assert_eq!(fetcher_counter, 1);
-        Ok(())
-    }
-
-    #[test]
-    fn caching_import_should_fetch_import_if_no_cache() -> Result<(), Error> {
-        let test_id = rand::thread_rng()
-            .sample_iter(Alphanumeric)
-            .take(36)
-            .collect::<String>();
-        let dir = temp_dir().join(test_id);
-
-        std::fs::create_dir_all(dir.as_path())?;
-
-        let cache = Cache::new_with_provider(|_| {
-            Ok(dir.clone().to_str().map(String::from).unwrap())
-        });
-
-        let import = Import {
-            mode: ImportMode::Code,
-            location: ImportTarget::Missing,
-            hash: Some(Hash::SHA256(hex::decode("d60d8415e36e86dae7f42933d3b0c4fe3ca238f057fba206c7e9fbf5d784fe15").unwrap())),
-        };
-
-        let mut fetcher_counter = 0;
-        let mut resolve_counter = 0;
-
-        let result = cache.caching_import(
-            &import,
-            || {
-                fetcher_counter += 1;
-                parse_str("1")
-            },
-            |parsed| {
-                resolve_counter += 1;
-                let result = parsed.resolve()?.typecheck()?;
-                Ok((result.normalize().to_hir(), result.ty))
-            },
-        );
-
-        assert!(result.is_ok(), "caching_import Should be valid");
-        assert_eq!(resolve_counter, 1);
-        assert_eq!(fetcher_counter, 1);
-
-        std::fs::remove_dir_all(dir.as_path()).unwrap();
-        Ok(())
-    }
-
-    #[test]
-    fn caching_import_should_fetch_import_on_cache_parsed_error(
-    ) -> Result<(), Error> {
-        let test_id = rand::thread_rng()
-            .sample_iter(Alphanumeric)
-            .take(36)
-            .collect::<String>();
-        let dir = temp_dir().join(test_id);
-
-        std::fs::create_dir_all(dir.as_path())?;
-
-        let cache = Cache::new_with_provider(|_| {
-            Ok(dir.clone().to_str().map(String::from).unwrap())
-        });
-
-        File::create(dir.join("dhall").join("1220d60d8415e36e86dae7f42933d3b0c4fe3ca238f057fba206c7e9fbf5d784fe15"))?
-            .write_all("Invalid content".as_bytes())?;
-
-        let import = Import {
-            mode: ImportMode::Code,
-            location: ImportTarget::Missing,
-            hash: Some(Hash::SHA256(hex::decode("d60d8415e36e86dae7f42933d3b0c4fe3ca238f057fba206c7e9fbf5d784fe15").unwrap())),
-        };
-
-        let mut fetcher_counter = 0;
-        let mut resolve_counter = 0;
-
-        let result = cache.caching_import(
-            &import,
-            || {
-                fetcher_counter += 1;
-                parse_str("1")
-            },
-            |parsed| {
-                resolve_counter += 1;
-                let result = parsed.resolve()?.typecheck()?;
-                Ok((result.normalize().to_hir(), result.ty))
-            },
-        );
-
-        assert!(result.is_ok(), "caching_import Should be valid");
-        assert_eq!(fetcher_counter, 1, "Should fetch since cache is invalid");
-        assert_eq!(
-            resolve_counter, 1,
-            "Should resolve only 1 time because cache can't be parsed"
-        );
-
-        std::fs::remove_dir_all(dir.as_path()).unwrap();
-        Ok(())
-    }
-
-    #[test]
-    fn caching_import_should_fetch_import_on_cache_resolve_error(
-    ) -> Result<(), Error> {
-        let test_id = rand::thread_rng()
-            .sample_iter(Alphanumeric)
-            .take(36)
-            .collect::<String>();
-        let dir = temp_dir().join(test_id);
-
-        std::fs::create_dir_all(dir.as_path())?;
-
-        let cache = Cache::new_with_provider(|_| {
-            Ok(dir.clone().to_str().map(String::from).unwrap())
-        });
-
-        let expr =
-            Expr::new(ExprKind::Num(NumKind::Natural(2)), Span::Artificial);
-        File::create(dir.join("dhall").join("1220d60d8415e36e86dae7f42933d3b0c4fe3ca238f057fba206c7e9fbf5d784fe15"))?
-            .write_all(binary::encode(&expr)?.as_slice())?;
-
-        let import = Import {
-            mode: ImportMode::Code,
-            location: ImportTarget::Missing,
-            hash: Some(Hash::SHA256(hex::decode("d60d8415e36e86dae7f42933d3b0c4fe3ca238f057fba206c7e9fbf5d784fe15").unwrap())),
-        };
-
-        let mut fetcher_counter = 0;
-        let mut resolve_counter = 0;
-
-        let result = cache.caching_import(
-            &import,
-            || {
-                fetcher_counter += 1;
-                parse_str("1")
-            },
-            |parsed| {
-                resolve_counter += 1;
-                match resolve_counter {
-                    1 => Err(Error::new(ErrorKind::Cache(
-                        CacheError::CacheHashInvalid,
-                    ))),
-                    _ => {
-                        let result = parsed.resolve()?.typecheck()?;
-                        Ok((result.normalize().to_hir(), result.ty))
-                    }
-                }
-            },
-        );
-
-        assert!(result.is_ok(), "caching_import Should be valid");
-        assert_eq!(fetcher_counter, 1, "Should fetch since cache is invalid");
-        assert_eq!(
-            resolve_counter, 2,
-            "Should resolve 2 time (one for cache that fail, one for fetch)"
-        );
-
-        std::fs::remove_dir_all(dir.as_path()).unwrap();
-        Ok(())
-    }
-
-    #[test]
-    fn caching_import_should_fetch_import_on_invalid_hash_cache_content(
-    ) -> Result<(), Error> {
-        let test_id = rand::thread_rng()
-            .sample_iter(Alphanumeric)
-            .take(36)
-            .collect::<String>();
-        let dir = temp_dir().join(test_id);
-
-        std::fs::create_dir_all(dir.as_path())?;
-
-        let cache = Cache::new_with_provider(|_| {
-            Ok(dir.clone().to_str().map(String::from).unwrap())
-        });
-
-        let expr =
-            Expr::new(ExprKind::Num(NumKind::Natural(2)), Span::Artificial);
-        File::create(dir.join("dhall").join("1220d60d8415e36e86dae7f42933d3b0c4fe3ca238f057fba206c7e9fbf5d784fe15"))?
-            .write_all(binary::encode(&expr)?.as_slice())?;
-
-        let import = Import {
-            mode: ImportMode::Code,
-            location: ImportTarget::Missing,
-            hash: Some(Hash::SHA256(hex::decode("d60d8415e36e86dae7f42933d3b0c4fe3ca238f057fba206c7e9fbf5d784fe15").unwrap())),
-        };
-
-        let mut fetcher_counter = 0;
-        let mut resolve_counter = 0;
-
-        let result = cache.caching_import(
-            &import,
-            || {
-                fetcher_counter += 1;
-                parse_str("1")
-            },
-            |parsed| {
-                resolve_counter += 1;
-                let result = parsed.resolve()?.typecheck()?;
-                Ok((result.normalize().to_hir(), result.ty))
-            },
-        );
-
-        assert!(result.is_ok(), "caching_import Should be valid");
-        assert_eq!(fetcher_counter, 1, "Should fetch since cache is invalid");
-        assert_eq!(
-            resolve_counter, 2,
-            "Should resolve 2 time (one for cache, one for fetch)"
-        );
-
-        std::fs::remove_dir_all(dir.as_path()).unwrap();
-        Ok(())
-    }
-
-    #[test]
-    fn caching_import_should_save_import_if_missing() -> Result<(), Error> {
-        let test_id = rand::thread_rng()
-            .sample_iter(Alphanumeric)
-            .take(36)
-            .collect::<String>();
-        let dir = temp_dir().join(test_id);
-
-        std::fs::create_dir_all(dir.as_path())?;
-
-        let cache = Cache::new_with_provider(|_| {
-            Ok(dir.clone().to_str().map(String::from).unwrap())
-        });
-        let import = Import {
-            mode: ImportMode::Code,
-            location: ImportTarget::Missing,
-            hash: Some(Hash::SHA256(hex::decode("d60d8415e36e86dae7f42933d3b0c4fe3ca238f057fba206c7e9fbf5d784fe15").unwrap())),
-        };
-
-        let mut fetcher_counter = 0;
-        let mut resolve_counter = 0;
-
-        let result = cache.caching_import(
-            &import,
-            || {
-                fetcher_counter += 1;
-                parse_str("1")
-            },
-            |parsed| {
-                resolve_counter += 1;
-                let result = parsed.resolve()?.typecheck()?;
-                Ok((result.normalize().to_hir(), result.ty))
-            },
-        );
-
-        assert!(result.is_ok(), "caching_import Should be valid");
-        assert_eq!(fetcher_counter, 1, "Should fetch since cache is mising");
-        assert_eq!(resolve_counter, 1, "Should resolve 1 time");
-
-        let cache_file = dir.join("dhall").join("1220d60d8415e36e86dae7f42933d3b0c4fe3ca238f057fba206c7e9fbf5d784fe15");
-        assert!(cache_file.exists());
-
-        std::fs::remove_dir_all(dir.as_path()).unwrap();
-        Ok(())
-    }
+    use crate::syntax::parse_expr;
 
     #[test]
-    fn cache_filename_should_result_for_hash() {
+    fn filename_for_hash_should_work() {
         let hash =
-            Hash::SHA256(parse_expr("1").unwrap().hash().unwrap().into_vec());
-        assert_eq!("1220d60d8415e36e86dae7f42933d3b0c4fe3ca238f057fba206c7e9fbf5d784fe15".to_string(), cache_filename(hash));
-    }
-
-    #[test]
-    fn check_hash_should_be_ok_for_same_hash() -> Result<(), Error> {
-        let typed = parse_str("1")?.resolve()?.typecheck()?;
-        let hash = Hash::SHA256(parse_expr("1")?.hash()?.into_vec());
-
-        let expected = (typed.normalize().to_hir(), typed.ty);
-        let actual = check_hash(&hash, expected.clone());
-        assert_eq!(actual.unwrap(), expected);
-        Ok(())
-    }
-
-    #[test]
-    fn check_hash_should_be_ok_for_unmatching_hash() -> Result<(), Error> {
-        let typed = parse_str("1")?.resolve()?.typecheck()?;
-        let hash = Hash::SHA256(parse_expr("2")?.hash()?.into_vec());
-
-        let expected = (typed.normalize().to_hir(), typed.ty);
-        let actual = check_hash(&hash, expected);
-        assert!(actual.is_err());
-        Ok(())
+            Hash::SHA256(parse_expr("1").unwrap().sha256_hash().unwrap());
+        assert_eq!("1220d60d8415e36e86dae7f42933d3b0c4fe3ca238f057fba206c7e9fbf5d784fe15".to_string(), filename_for_hash(&hash));
     }
 }
diff --git a/dhall/src/semantics/resolve/env.rs b/dhall/src/semantics/resolve/env.rs
index 4d502ce..06e27a5 100644
--- a/dhall/src/semantics/resolve/env.rs
+++ b/dhall/src/semantics/resolve/env.rs
@@ -2,7 +2,7 @@ use std::collections::HashMap;
 
 use crate::error::{Error, ImportError};
 use crate::semantics::{AlphaVar, Cache, ImportLocation, TypedHir, VarEnv};
-use crate::syntax::{Label, V};
+use crate::syntax::{Hash, Label, V};
 
 /// Environment for resolving names.
 #[derive(Debug, Clone, Default)]
@@ -16,7 +16,7 @@ pub type CyclesStack = Vec<ImportLocation>;
 /// Environment for resolving imports
 #[derive(Debug)]
 pub struct ImportEnv {
-    pub file_cache: Cache,
+    file_cache: Option<Cache>,
     mem_cache: MemCache,
     stack: CyclesStack,
 }
@@ -68,20 +68,36 @@ impl NameEnv {
 impl ImportEnv {
     pub fn new() -> Self {
         ImportEnv {
-            file_cache: Cache::new(),
+            file_cache: Cache::new().ok(),
             mem_cache: Default::default(),
             stack: Default::default(),
         }
     }
 
-    pub fn get_from_cache<'a>(
-        &'a self,
+    pub fn get_from_cache(
+        &mut self,
         location: &ImportLocation,
-    ) -> Option<&'a TypedHir> {
-        self.mem_cache.get(location)
+        hash: Option<&Hash>,
+    ) -> Option<TypedHir> {
+        if let Some(expr) = self.mem_cache.get(location) {
+            return Some(expr.clone());
+        }
+        let hash = hash.as_ref()?;
+        let expr = self.file_cache.as_ref()?.get(hash).ok()?;
+        Some(expr)
     }
 
-    pub fn set_cache(&mut self, location: ImportLocation, expr: TypedHir) {
+    pub fn set_cache(
+        &mut self,
+        location: ImportLocation,
+        hash: Option<&Hash>,
+        expr: TypedHir,
+    ) {
+        if let Some(file_cache) = self.file_cache.as_ref() {
+            if let Some(hash) = hash {
+                let _ = file_cache.insert(hash, &expr);
+            }
+        }
         self.mem_cache.insert(location, expr);
     }
 
diff --git a/dhall/src/semantics/resolve/resolve.rs b/dhall/src/semantics/resolve/resolve.rs
index 8f8a9fe..d6bc4cd 100644
--- a/dhall/src/semantics/resolve/resolve.rs
+++ b/dhall/src/semantics/resolve/resolve.rs
@@ -220,6 +220,32 @@ fn make_aslocation_uniontype() -> Expr {
     mkexpr(ExprKind::UnionType(union))
 }
 
+fn check_hash(
+    import: &Import,
+    typed: &TypedHir,
+    span: Span,
+) -> Result<(), Error> {
+    match (import.mode, &import.hash) {
+        (ImportMode::Code, Some(Hash::SHA256(hash))) => {
+            let actual_hash = typed.0.to_expr_alpha().sha256_hash()?;
+            if hash[..] != actual_hash[..] {
+                mkerr(
+                    ErrorBuilder::new("hash mismatch")
+                        .span_err(span, "hash mismatch")
+                        .note(format!("Expected sha256:{}", hex::encode(hash)))
+                        .note(format!(
+                            "Found    sha256:{}",
+                            hex::encode(actual_hash)
+                        ))
+                        .format(),
+                )?
+            }
+        }
+        _ => {}
+    }
+    Ok(())
+}
+
 fn resolve_one_import(
     env: &mut ImportEnv,
     import: &Import,
@@ -228,44 +254,15 @@ fn resolve_one_import(
 ) -> Result<TypedHir, Error> {
     match import.mode {
         ImportMode::Code => {
-            let (hir, ty) = env.file_cache.clone().caching_import(
-                import,
-                || location.fetch_dhall(),
-                |parsed| {
-                    let typed = resolve_with_env(env, parsed)?.typecheck()?;
-                    let hir = typed.normalize().to_hir();
-                    Ok((hir, typed.ty))
-                },
-            )?;
-            match &import.hash {
-                Some(Hash::SHA256(hash)) => {
-                    let actual_hash = hir.to_expr_alpha().hash()?;
-                    if hash[..] != actual_hash[..] {
-                        mkerr(
-                            ErrorBuilder::new("hash mismatch")
-                                .span_err(span, "hash mismatch")
-                                .note(format!(
-                                    "Expected sha256:{}",
-                                    hex::encode(hash)
-                                ))
-                                .note(format!(
-                                    "Found    sha256:{}",
-                                    hex::encode(actual_hash)
-                                ))
-                                .format(),
-                        )?
-                    }
-                }
-                None => {}
-            }
-            Ok((hir, ty))
+            let parsed = location.fetch_dhall()?;
+            let typed = resolve_with_env(env, parsed)?.typecheck()?;
+            let hir = typed.normalize().to_hir();
+            Ok((hir, typed.ty))
         }
         ImportMode::RawText => {
             let text = location.fetch_text()?;
-            let hir = Hir::new(
-                HirKind::Expr(ExprKind::TextLit(text.into())),
-                Span::Artificial,
-            );
+            let hir =
+                Hir::new(HirKind::Expr(ExprKind::TextLit(text.into())), span);
             Ok((hir, Type::from_builtin(Builtin::Text)))
         }
         ImportMode::Location => {
@@ -399,15 +396,20 @@ fn resolve_with_env(
             let do_sanity_check = import.mode != ImportMode::Location;
             let location =
                 base_location.chain(&import.location, do_sanity_check)?;
-            if let Some(expr) = env.get_from_cache(&location) {
-                return Ok(expr.clone());
+            // If the import is in the in-memory cache, or the hash is in the on-disk cache, return
+            // the cached contents.
+            if let Some(resolved) =
+                env.get_from_cache(&location, import.hash.as_ref())
+            {
+                return Ok(resolved);
             }
-            let expr = env.with_cycle_detection(location.clone(), |env| {
-                resolve_one_import(env, &import, location.clone(), span)
+            let typed = env.with_cycle_detection(location.clone(), |env| {
+                resolve_one_import(env, &import, location.clone(), span.clone())
             })?;
-            // Add the resolved import to the cache
-            env.set_cache(location, expr.clone());
-            Ok(expr)
+            check_hash(&import, &typed, span)?;
+            // Add the resolved import to the caches
+            env.set_cache(location, import.hash.as_ref(), typed.clone());
+            Ok(typed)
         },
     )?;
     Ok(Resolved(resolved))
diff --git a/dhall/src/syntax/ast/expr.rs b/dhall/src/syntax/ast/expr.rs
index b1a978f..eba2735 100644
--- a/dhall/src/syntax/ast/expr.rs
+++ b/dhall/src/syntax/ast/expr.rs
@@ -178,10 +178,9 @@ impl Expr {
     }
 
     // Compute the sha256 hash of the binary form of the expression.
-    pub fn hash(&self) -> Result<Box<[u8]>, Error> {
-        use sha2::Digest;
+    pub fn sha256_hash(&self) -> Result<Box<[u8]>, Error> {
         let data = binary::encode(self)?;
-        Ok(sha2::Sha256::digest(&data).as_slice().into())
+        Ok(crate::utils::sha256_hash(&data))
     }
 }
 
diff --git a/dhall/src/syntax/ast/import.rs b/dhall/src/syntax/ast/import.rs
index c45fe51..69f4021 100644
--- a/dhall/src/syntax/ast/import.rs
+++ b/dhall/src/syntax/ast/import.rs
@@ -52,7 +52,7 @@ pub enum ImportMode {
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub enum Hash {
-    SHA256(Vec<u8>),
+    SHA256(Box<[u8]>),
 }
 
 /// Reference to an external resource
diff --git a/dhall/src/syntax/binary/decode.rs b/dhall/src/syntax/binary/decode.rs
index f4747d3..4ea7d98 100644
--- a/dhall/src/syntax/binary/decode.rs
+++ b/dhall/src/syntax/binary/decode.rs
@@ -290,7 +290,7 @@ fn cbor_value_to_dhall(data: &Value) -> Result<DecodedExpr, DecodeError> {
                     Null => None,
                     Bytes(bytes) => match bytes.as_slice() {
                         [18, 32, rest @ ..] => {
-                            Some(Hash::SHA256(rest.to_vec()))
+                            Some(Hash::SHA256(rest.to_vec().into()))
                         }
                         _ => {
                             return Err(DecodeError::WrongFormatError(format!(
diff --git a/dhall/src/syntax/text/parser.rs b/dhall/src/syntax/text/parser.rs
index 37f28e5..07921b5 100644
--- a/dhall/src/syntax/text/parser.rs
+++ b/dhall/src/syntax/text/parser.rs
@@ -593,7 +593,7 @@ impl DhallParser {
                 input.error(format!("Unknown hashing protocol '{}'", protocol))
             );
         }
-        Ok(Hash::SHA256(hex::decode(hash).unwrap()))
+        Ok(Hash::SHA256(hex::decode(hash).unwrap().into()))
     }
 
     fn import_hashed(
diff --git a/dhall/src/utils.rs b/dhall/src/utils.rs
new file mode 100644
index 0000000..d1e642a
--- /dev/null
+++ b/dhall/src/utils.rs
@@ -0,0 +1,17 @@
+use std::fs::File;
+use std::io::Read;
+use std::path::Path;
+
+use crate::error::Error;
+
+// Compute the sha256 hash of a bitstring.
+pub fn sha256_hash(data: &[u8]) -> Box<[u8]> {
+    use sha2::Digest;
+    sha2::Sha256::digest(data).as_slice().into()
+}
+
+pub fn read_binary_file(path: impl AsRef<Path>) -> Result<Box<[u8]>, Error> {
+    let mut buffer = Vec::new();
+    File::open(path)?.read_to_end(&mut buffer)?;
+    Ok(buffer.into())
+}
diff --git a/dhall/tests/spec.rs b/dhall/tests/spec.rs
index 8d67892..ae53f4a 100644
--- a/dhall/tests/spec.rs
+++ b/dhall/tests/spec.rs
@@ -670,7 +670,7 @@ fn run_test(test: &SpecTest) -> Result<()> {
         }
         SemanticHash => {
             let expr = expr.normalize()?.to_expr_alpha();
-            let hash = hex::encode(expr.hash()?);
+            let hash = hex::encode(expr.sha256_hash()?);
             expected.compare_ui(format!("sha256:{}", hash))?;
         }
         TypeInferenceSuccess => {