Auto merge of #6493 - ehuss:fix-fingerprint-patch, r=alexcrichton

Fix fingerprint calculation for patched deps.

If you have A→B→C where B and C are in a registry, and you `[patch]` C, the fingerprint calculation wasn't working correctly when C changes. The following sequence illustrates the problem:

1. Do a build from scratch.
2. Touch a file in C.
3. Build again. Everything rebuilds as expected.
4. Build again. You would expect this to be all fresh, but it rebuilds A.

The problem is the hash-busting doesn't propagate up to parents from dependencies. Normal targets normally aren't a problem because they have a `LocalFingerprint::MtimeBased` style local value which always recomputes the hash. However, registry dependencies have a `Precalculated` style local value which never recomputes the hash.

The solution here is to always recompute the hash. This shouldn't be too expensive, and is only done when writing the fingerprint, which should only happen when the target is dirty. I'm not entirely certain why the caching logic was added in #4125.

Fixes rust-lang/rust#57142

src/cargo/core/compiler/fingerprint.rs

@@ -236,7 +236,6 @@ impl Fingerprint {
     }
 
     fn update_local(&self, root: &Path) -> CargoResult<()> {
-        let mut hash_busted = false;
         for local in self.local.iter() {
             match *local {
                 LocalFingerprint::MtimeBased(ref slot, ref path) => {
@@ -246,12 +245,9 @@ impl Fingerprint {
                 }
                 LocalFingerprint::EnvBased(..) | LocalFingerprint::Precalculated(..) => continue,
             }
-            hash_busted = true;
         }
 
-        if hash_busted {
-            *self.memoized_hash.lock().unwrap() = None;
-        }
+        *self.memoized_hash.lock().unwrap() = None;
         Ok(())
     }
 

tests/testsuite/freshness.rs

@@ -4,7 +4,7 @@ use std::io::prelude::*;
 use crate::support::paths::CargoPathExt;
 use crate::support::registry::Package;
 use crate::support::sleep_ms;
-use crate::support::{basic_manifest, project};
+use crate::support::{basic_manifest, is_coarse_mtime, project};
 
 #[test]
 fn modifying_and_moving() {
@@ -1252,3 +1252,60 @@ fn reuse_panic_pm() {
         )
         .run();
 }
+
+#[test]
+fn bust_patched_dep() {
+    Package::new("registry1", "0.1.0").publish();
+    Package::new("registry2", "0.1.0")
+        .dep("registry1", "0.1.0")
+        .publish();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.0.1"
+
+            [dependencies]
+            registry2 = "0.1.0"
+
+            [patch.crates-io]
+            registry1 = { path = "reg1new" }
+        "#,
+        )
+        .file("src/lib.rs", "")
+        .file("reg1new/Cargo.toml", &basic_manifest("registry1", "0.1.0"))
+        .file("reg1new/src/lib.rs", "")
+        .build();
+
+    p.cargo("build").run();
+
+    File::create(&p.root().join("reg1new/src/lib.rs")).unwrap();
+    if is_coarse_mtime() {
+        sleep_ms(1000);
+    }
+
+    p.cargo("build")
+        .with_stderr(
+            "\
+[COMPILING] registry1 v0.1.0 ([..])
+[COMPILING] registry2 v0.1.0
+[COMPILING] foo v0.0.1 ([..])
+[FINISHED] [..]
+",
+        )
+        .run();
+
+    p.cargo("build -v")
+        .with_stderr(
+            "\
+[FRESH] registry1 v0.1.0 ([..])
+[FRESH] registry2 v0.1.0
+[FRESH] foo v0.0.1 ([..])
+[FINISHED] [..]
+",
+        )
+        .run();
+}