Auto merge of #14137 - Xaeroxe:checksum-freshness, r=weihanglo

initial version of checksum based freshness

Implementation for #14136 and resolves #6529

This PR implements the use of checksums in cargo fingerprints as an alternative to using mtimes. This is most useful on systems with poor mtime implementations.

This has a dependency on rust-lang/rust#126930. It's expected this will increase the time it takes to declare a build to be fresh. Still this loss in performance may be preferable to the issues the ecosystem has had with the use of mtimes for determining freshness.

Cargo.toml

@@ -23,6 +23,7 @@ anstream = "0.6.15"
 anstyle = "1.0.8"
 anyhow = "1.0.86"
 base64 = "0.22.1"
+blake3 = "1.5.2"
 bytesize = "1.3"
 cargo = { path = "" }
 cargo-credential = { version = "0.4.2", path = "credential/cargo-credential" }
@@ -148,6 +149,7 @@ anstream.workspace = true
 anstyle.workspace = true
 anyhow.workspace = true
 base64.workspace = true
+blake3.workspace = true
 bytesize.workspace = true
 cargo-credential.workspace = true
 cargo-platform.workspace = true
@@ -197,6 +199,7 @@ shell-escape.workspace = true
 supports-hyperlinks.workspace = true
 tar.workspace = true
 tempfile.workspace = true
+thiserror.workspace = true
 time.workspace = true
 toml.workspace = true
 toml_edit.workspace = true

crates/cargo-test-support/src/lib.rs

@@ -1582,3 +1582,82 @@ where
     let thread = std::thread::spawn(|| f());
     thread_wait_timeout(n, thread)
 }
+
+// Helper for testing dep-info files in the fingerprint dir.
+#[track_caller]
+pub fn assert_deps(project: &Project, fingerprint: &str, test_cb: impl Fn(&Path, &[(u8, &str)])) {
+    let mut files = project
+        .glob(fingerprint)
+        .map(|f| f.expect("unwrap glob result"))
+        // Filter out `.json` entries.
+        .filter(|f| f.extension().is_none());
+    let info_path = files
+        .next()
+        .unwrap_or_else(|| panic!("expected 1 dep-info file at {}, found 0", fingerprint));
+    assert!(files.next().is_none(), "expected only 1 dep-info file");
+    let dep_info = fs::read(&info_path).unwrap();
+    let dep_info = &mut &dep_info[..];
+    let deps = (0..read_usize(dep_info))
+        .map(|_| {
+            let ty = read_u8(dep_info);
+            let path = std::str::from_utf8(read_bytes(dep_info)).unwrap();
+            let checksum_present = read_bool(dep_info);
+            if checksum_present {
+                // Read out the checksum info without using it
+                let _file_len = read_u64(dep_info);
+                let _checksum = read_bytes(dep_info);
+            }
+            (ty, path)
+        })
+        .collect::<Vec<_>>();
+    test_cb(&info_path, &deps);
+
+    fn read_usize(bytes: &mut &[u8]) -> usize {
+        let ret = &bytes[..4];
+        *bytes = &bytes[4..];
+
+        u32::from_le_bytes(ret.try_into().unwrap()) as usize
+    }
+
+    fn read_u8(bytes: &mut &[u8]) -> u8 {
+        let ret = bytes[0];
+        *bytes = &bytes[1..];
+        ret
+    }
+
+    fn read_bool(bytes: &mut &[u8]) -> bool {
+        read_u8(bytes) != 0
+    }
+
+    fn read_u64(bytes: &mut &[u8]) -> u64 {
+        let ret = &bytes[..8];
+        *bytes = &bytes[8..];
+
+        u64::from_le_bytes(ret.try_into().unwrap())
+    }
+
+    fn read_bytes<'a>(bytes: &mut &'a [u8]) -> &'a [u8] {
+        let n = read_usize(bytes);
+        let ret = &bytes[..n];
+        *bytes = &bytes[n..];
+        ret
+    }
+}
+
+pub fn assert_deps_contains(project: &Project, fingerprint: &str, expected: &[(u8, &str)]) {
+    assert_deps(project, fingerprint, |info_path, entries| {
+        for (e_kind, e_path) in expected {
+            let pattern = glob::Pattern::new(e_path).unwrap();
+            let count = entries
+                .iter()
+                .filter(|(kind, path)| kind == e_kind && pattern.matches(path))
+                .count();
+            if count != 1 {
+                panic!(
+                    "Expected 1 match of {} {} in {:?}, got {}:\n{:#?}",
+                    e_kind, e_path, info_path, count, entries
+                );
+            }
+        }
+    })
+}

deny.toml

@@ -94,6 +94,7 @@ allow = [
     "MIT",
     "MIT-0",
     "Apache-2.0",
+    "BSD-2-Clause",
     "BSD-3-Clause",
     "MPL-2.0",
     "Unicode-DFS-2016",

src/cargo/core/compiler/build_runner/mod.rs

@@ -16,7 +16,7 @@ use jobserver::Client;
 
 use super::build_plan::BuildPlan;
 use super::custom_build::{self, BuildDeps, BuildScriptOutputs, BuildScripts};
-use super::fingerprint::Fingerprint;
+use super::fingerprint::{Checksum, Fingerprint};
 use super::job_queue::JobQueue;
 use super::layout::Layout;
 use super::lto::Lto;
@@ -50,6 +50,8 @@ pub struct BuildRunner<'a, 'gctx> {
     pub fingerprints: HashMap<Unit, Arc<Fingerprint>>,
     /// Cache of file mtimes to reduce filesystem hits.
     pub mtime_cache: HashMap<PathBuf, FileTime>,
+    /// Cache of file checksums to reduce filesystem reads.
+    pub checksum_cache: HashMap<PathBuf, Checksum>,
     /// A set used to track which units have been compiled.
     /// A unit may appear in the job graph multiple times as a dependency of
     /// multiple packages, but it only needs to run once.
@@ -113,6 +115,7 @@ impl<'a, 'gctx> BuildRunner<'a, 'gctx> {
             build_script_outputs: Arc::new(Mutex::new(BuildScriptOutputs::default())),
             fingerprints: HashMap::new(),
             mtime_cache: HashMap::new(),
+            checksum_cache: HashMap::new(),
             compiled: HashSet::new(),
             build_scripts: HashMap::new(),
             build_explicit_deps: HashMap::new(),

src/cargo/core/compiler/fingerprint/dirty_reason.rs

@@ -34,6 +34,9 @@ pub enum DirtyReason {
         old: String,
         new: String,
     },
+    ChecksumUseChanged {
+        old: bool,
+    },
     DepInfoOutputChanged {
         old: PathBuf,
         new: PathBuf,
@@ -183,6 +186,16 @@ impl DirtyReason {
             DirtyReason::PrecalculatedComponentsChanged { .. } => {
                 s.dirty_because(unit, "the precalculated components changed")
             }
+            DirtyReason::ChecksumUseChanged { old } => {
+                if *old {
+                    s.dirty_because(
+                        unit,
+                        "the prior compilation used checksum freshness and this one does not",
+                    )
+                } else {
+                    s.dirty_because(unit, "checksum freshness requested, prior compilation did not use checksum freshness")
+                }
+            }
             DirtyReason::DepInfoOutputChanged { .. } => {
                 s.dirty_because(unit, "the dependency info output changed")
             }
@@ -222,6 +235,20 @@ impl DirtyReason {
                             format_args!("the file `{}` is missing", file.display()),
                         )
                     }
+                    StaleItem::UnableToReadFile(file) => {
+                        let file = file.strip_prefix(root).unwrap_or(&file);
+                        s.dirty_because(
+                            unit,
+                            format_args!("the file `{}` could not be read", file.display()),
+                        )
+                    }
+                    StaleItem::FailedToReadMetadata(file) => {
+                        let file = file.strip_prefix(root).unwrap_or(&file);
+                        s.dirty_because(
+                            unit,
+                            format_args!("couldn't read metadata for file `{}`", file.display()),
+                        )
+                    }
                     StaleItem::ChangedFile {
                         stale,
                         stale_mtime,
@@ -235,6 +262,41 @@ impl DirtyReason {
                             format_args!("the file `{}` has changed ({after})", file.display()),
                         )
                     }
+                    StaleItem::ChangedChecksum {
+                        source,
+                        stored_checksum,
+                        new_checksum,
+                    } => {
+                        let file = source.strip_prefix(root).unwrap_or(&source);
+                        s.dirty_because(
+                            unit,
+                            format_args!(
+                                "the file `{}` has changed (checksum didn't match, {stored_checksum} != {new_checksum})",
+                                file.display(),
+                            ),
+                        )
+                    }
+                    StaleItem::FileSizeChanged {
+                        path,
+                        old_size,
+                        new_size,
+                    } => {
+                        let file = path.strip_prefix(root).unwrap_or(&path);
+                        s.dirty_because(
+                            unit,
+                            format_args!(
+                                "file size changed ({old_size} != {new_size}) for `{}`",
+                                file.display()
+                            ),
+                        )
+                    }
+                    StaleItem::MissingChecksum(path) => {
+                        let file = path.strip_prefix(root).unwrap_or(&path);
+                        s.dirty_because(
+                            unit,
+                            format_args!("the checksum for file `{}` is missing", file.display()),
+                        )
+                    }
                     StaleItem::ChangedEnv { var, .. } => s.dirty_because(
                         unit,
                         format_args!("the environment variable {var} changed"),