[WIP] File hashing

Author: bjorn3

build_system/hash.rs

@@ -0,0 +1,49 @@
+#[allow(deprecated)]
+use std::hash::SipHasher;
+use std::hash::{Hash, Hasher};
+use std::path::Path;
+
+#[derive(Copy, Clone, Debug)]
+pub(crate) enum IsDirty {
+    Clean,
+    Dirty,
+}
+
+impl IsDirty {
+    pub(crate) fn check_file(file: &Path, expected_hash: u64) -> Self {
+        let contents = std::fs::read(file).unwrap();
+
+        #[allow(deprecated)]
+        let mut hasher = SipHasher::new();
+        contents.hash(&mut hasher);
+        let actual_hash = hasher.finish();
+
+        if actual_hash == expected_hash { IsDirty::Clean } else { IsDirty::Dirty }
+    }
+}
+
+pub(crate) struct HashedFile {
+    contents: Vec<u8>,
+    hash: u64,
+}
+
+impl HashedFile {
+    pub(crate) fn read_file(file: &Path) -> Self {
+        let contents = std::fs::read(file).unwrap();
+
+        #[allow(deprecated)]
+        let mut hasher = SipHasher::new();
+        contents.hash(&mut hasher);
+        let hash = hasher.finish();
+
+        HashedFile { contents, hash }
+    }
+
+    pub(crate) fn write_if_changed(&self, target: &Path) -> IsDirty {
+        let is_dirty = IsDirty::check_file(target, self.hash);
+        if let IsDirty::Dirty = is_dirty {
+            std::fs::write(target, &self.contents).unwrap();
+        }
+        is_dirty
+    }
+}

build_system/main.rs

@@ -13,6 +13,7 @@ mod bench;
 mod build_backend;
 mod build_sysroot;
 mod config;
+mod hash;
 mod path;
 mod prepare;
 mod rustc_info;