Auto merge of #8755 - ehuss:fingerprint-lto, r=alexcrichton

Add LTO to the metadata filename hash.

There are some rare cases where different cargo commands end up building dependencies with different LTO settings. This adds the LTO value to the filename hash so that the cache does not thrash when switching between these commands.

Fixes #8669

Author: bors

src/cargo/core/compiler/context/compilation_files.rs

@@ -519,6 +519,7 @@ fn compute_metadata(
     // settings like debuginfo and whatnot.
     unit.profile.hash(&mut hasher);
     unit.mode.hash(&mut hasher);
+    cx.lto[unit].hash(&mut hasher);
 
     // Artifacts compiled for the host should have a different metadata
     // piece than those compiled for the target, so make sure we throw in

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

@@ -126,10 +126,10 @@ impl<'a, 'cfg> Context<'a, 'cfg> {
         let mut queue = JobQueue::new(self.bcx);
         let mut plan = BuildPlan::new();
         let build_plan = self.bcx.build_config.build_plan;
+        self.lto = super::lto::generate(&self.bcx)?;
         self.prepare_units()?;
         self.prepare()?;
         custom_build::build_map(&mut self)?;
-        super::lto::generate(&mut self)?;
         self.check_collistions()?;
 
         for unit in &self.bcx.roots {

src/cargo/core/compiler/fingerprint.rs

@@ -72,7 +72,7 @@
 //! -C incremental=… flag                      | ✓           |
 //! mtime of sources                           | ✓[^3]       |
 //! RUSTFLAGS/RUSTDOCFLAGS                     | ✓           |
-//! LTO flags                                  | ✓           |
+//! LTO flags                                  | ✓           | ✓
 //! config settings[^5]                        | ✓           |
 //! is_std                                     |             | ✓
 //!

src/cargo/core/compiler/lto.rs

@@ -1,4 +1,4 @@
-use crate::core::compiler::{CompileMode, Context, CrateType, Unit};
+use crate::core::compiler::{BuildContext, CompileMode, CrateType, Unit};
 use crate::core::profiles;
 use crate::util::interning::InternedString;
 
@@ -40,9 +40,9 @@ pub enum Lto {
     OnlyObject,
 }
 
-pub fn generate(cx: &mut Context<'_, '_>) -> CargoResult<()> {
+pub fn generate(bcx: &BuildContext<'_, '_>) -> CargoResult<HashMap<Unit, Lto>> {
     let mut map = HashMap::new();
-    for unit in cx.bcx.roots.iter() {
+    for unit in bcx.roots.iter() {
         let root_lto = match unit.profile.lto {
             // LTO not requested, no need for bitcode.
             profiles::Lto::Bool(false) | profiles::Lto::Off => Lto::OnlyObject,
@@ -60,10 +60,9 @@ pub fn generate(cx: &mut Context<'_, '_>) -> CargoResult<()> {
                 }
             }
         };
-        calculate(cx, &mut map, unit, root_lto)?;
+        calculate(bcx, &mut map, unit, root_lto)?;
     }
-    cx.lto = map;
-    Ok(())
+    Ok(map)
 }
 
 /// Whether or not any of these crate types need object code.
@@ -87,7 +86,7 @@ fn lto_when_needs_object(crate_types: &[CrateType]) -> Lto {
 }
 
 fn calculate(
-    cx: &Context<'_, '_>,
+    bcx: &BuildContext<'_, '_>,
     map: &mut HashMap<Unit, Lto>,
     unit: &Unit,
     parent_lto: Lto,
@@ -185,8 +184,8 @@ fn calculate(
         }
     };
 
-    for dep in cx.unit_deps(unit) {
-        calculate(cx, map, &dep.unit, merged_lto)?;
+    for dep in &bcx.unit_graph[unit] {
+        calculate(bcx, map, &dep.unit, merged_lto)?;
     }
     Ok(())
 }

tests/testsuite/lto.rs

@@ -778,3 +778,78 @@ fn dylib_rlib_bin() {
     );
     verify_lto(&output, "foo", "--crate-type bin", Lto::Run(None));
 }
+
+#[cargo_test]
+fn fresh_swapping_commands() {
+    // In some rare cases, different commands end up building dependencies
+    // with different LTO settings. This checks that it doesn't cause the
+    // cache to thrash in that scenario.
+    Package::new("bar", "1.0.0").publish();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.1.0"
+
+                [dependencies]
+                bar = "1.0"
+
+                [profile.release]
+                lto = true
+            "#,
+        )
+        .file("src/lib.rs", "pub fn foo() { println!(\"hi!\"); }")
+        .build();
+
+    p.cargo("build --release -v")
+        .with_stderr(
+            "\
+[UPDATING] [..]
+[DOWNLOADING] crates ...
+[DOWNLOADED] bar v1.0.0 [..]
+[COMPILING] bar v1.0.0
+[RUNNING] `rustc --crate-name bar [..]-C linker-plugin-lto[..]
+[COMPILING] foo v0.1.0 [..]
+[RUNNING] `rustc --crate-name foo src/lib.rs [..]-C linker-plugin-lto[..]
+[FINISHED] [..]
+",
+        )
+        .run();
+    p.cargo("test --release -v")
+        .with_stderr_unordered(
+            "\
+[COMPILING] bar v1.0.0
+[RUNNING] `rustc --crate-name bar [..]-C embed-bitcode=no[..]
+[COMPILING] foo v0.1.0 [..]
+[RUNNING] `rustc --crate-name foo src/lib.rs [..]--crate-type lib[..]-C embed-bitcode=no[..]
+[RUNNING] `rustc --crate-name foo src/lib.rs [..]-C embed-bitcode=no[..]--test[..]
+[FINISHED] [..]
+[RUNNING] `[..]/foo[..]`
+[DOCTEST] foo
+[RUNNING] `rustdoc [..]-C embed-bitcode=no[..]
+",
+        )
+        .run();
+
+    p.cargo("build --release -v")
+        .with_stderr(
+            "\
+[FRESH] bar v1.0.0
+[FRESH] foo [..]
+[FINISHED] [..]
+",
+        )
+        .run();
+    p.cargo("test --release -v --no-run -v")
+        .with_stderr(
+            "\
+[FRESH] bar v1.0.0
+[FRESH] foo [..]
+[FINISHED] [..]
+",
+        )
+        .run();
+}