Remove Freshness from DependencyQueue

Ever since the inception of Cargo and the advent of incremental
compilation at the crate level via Cargo, Cargo has tracked whether it
needs to recompile something at a unit level in its "dependency queue"
which manages when items are ready for execution. Over time we've fixed
lots and lots of bugs related to incremental compilation, and perhaps
one of the most impactful realizations was that the model Cargo started
with fundamentally doesn't handle interrupting Cargo halfway through and
resuming the build later.

The previous model relied upon implicitly propagating "dirtiness" based
on whether the one of the dependencies of a build was rebuilt or not.
This information is not available, however, if Cargo is interrupted and
resumed (or performs a subset of steps and then later performs more).
We've fixed this in a number of places historically but the purpose of
this commit is to put a nail in this coffin once and for all.

Implicit propagation of whether a unit is fresh or dirty is no longer
present at all. Instead Cargo should always know, irrespective of it's
in-memory state, whether a unit needs to be recompiled or not. This
commit actually turns up a few bugs in the test suite, so later commits
will be targeted at fixing this.

Note that this required a good deal of work on the `fingerprint` module
to fix some longstanding bugs (like #6780) and some serious hoops had to
be jumped through for others (like #6779). While these were fallout from
this change they weren't necessarily the primary motivation, but rather
to help make `fingerprints` a bit more straightforward in what's an
already confusing system!

Closes #6780

src/cargo/core/compiler/custom_build.rs

@@ -8,10 +8,10 @@ use std::sync::{Arc, Mutex};
 use crate::core::PackageId;
 use crate::util::errors::{CargoResult, CargoResultExt};
 use crate::util::machine_message;
+use crate::util::Cfg;
 use crate::util::{self, internal, paths, profile};
-use crate::util::{Cfg, Freshness};
 
-use super::job::Work;
+use super::job::{Freshness, Job, Work};
 use super::{fingerprint, Context, Kind, TargetConfig, Unit};
 
 /// Contains the parsed output of a custom build script.
@@ -80,32 +80,19 @@ pub struct BuildDeps {
 /// prepare work for. If the requirement is specified as both the target and the
 /// host platforms it is assumed that the two are equal and the build script is
 /// only run once (not twice).
-pub fn prepare<'a, 'cfg>(
-    cx: &mut Context<'a, 'cfg>,
-    unit: &Unit<'a>,
-) -> CargoResult<(Work, Work, Freshness)> {
+pub fn prepare<'a, 'cfg>(cx: &mut Context<'a, 'cfg>, unit: &Unit<'a>) -> CargoResult<Job> {
     let _p = profile::start(format!(
         "build script prepare: {}/{}",
         unit.pkg,
         unit.target.name()
     ));
 
     let key = (unit.pkg.package_id(), unit.kind);
-    let overridden = cx.build_script_overridden.contains(&key);
-    let (work_dirty, work_fresh) = if overridden {
-        (Work::noop(), Work::noop())
-    } else {
-        build_work(cx, unit)?
-    };
 
-    if cx.bcx.build_config.build_plan {
-        Ok((work_dirty, work_fresh, Freshness::Dirty))
+    if cx.build_script_overridden.contains(&key) {
+        fingerprint::prepare_target(cx, unit, false)
     } else {
-        // Now that we've prep'd our work, build the work needed to manage the
-        // fingerprint and then start returning that upwards.
-        let (freshness, dirty, fresh) = fingerprint::prepare_build_cmd(cx, unit)?;
-
-        Ok((work_dirty.then(dirty), work_fresh.then(fresh), freshness))
+        build_work(cx, unit)
     }
 }
 
@@ -125,7 +112,7 @@ fn emit_build_output(output: &BuildOutput, package_id: PackageId) {
     });
 }
 
-fn build_work<'a, 'cfg>(cx: &mut Context<'a, 'cfg>, unit: &Unit<'a>) -> CargoResult<(Work, Work)> {
+fn build_work<'a, 'cfg>(cx: &mut Context<'a, 'cfg>, unit: &Unit<'a>) -> CargoResult<Job> {
     assert!(unit.mode.is_run_custom_build());
     let bcx = &cx.bcx;
     let dependencies = cx.dep_targets(unit);
@@ -261,21 +248,19 @@ fn build_work<'a, 'cfg>(cx: &mut Context<'a, 'cfg>, unit: &Unit<'a>) -> CargoRes
     let json_messages = bcx.build_config.json_messages();
     let extra_verbose = bcx.config.extra_verbose();
 
-    // Check to see if the build script has already run, and if it has, keep
-    // track of whether it has told us about some explicit dependencies.
-    let prev_script_out_dir = paths::read_bytes(&root_output_file)
-        .and_then(|bytes| util::bytes2path(&bytes))
-        .unwrap_or_else(|_| script_out_dir.clone());
-
-    let prev_output = BuildOutput::parse_file(
-        &output_file,
-        &pkg_name,
-        &prev_script_out_dir,
-        &script_out_dir,
-    )
-    .ok();
-    let deps = BuildDeps::new(&output_file, prev_output.as_ref());
-    cx.build_explicit_deps.insert(*unit, deps);
+    // TODO: no duplicate
+        let prev_script_out_dir = paths::read_bytes(&root_output_file)
+            .and_then(|bytes| util::bytes2path(&bytes))
+            .unwrap_or_else(|_| script_out_dir.clone());
+
+    // TODO: no duplicate
+        let prev_output = BuildOutput::parse_file(
+            &output_file,
+            &unit.pkg.to_string(),
+            &prev_script_out_dir,
+            &script_out_dir,
+        )
+        .ok();
 
     fs::create_dir_all(&script_dir)?;
     fs::create_dir_all(&script_out_dir)?;
@@ -392,7 +377,17 @@ fn build_work<'a, 'cfg>(cx: &mut Context<'a, 'cfg>, unit: &Unit<'a>) -> CargoRes
         Ok(())
     });
 
-    Ok((dirty, fresh))
+    let mut job = if cx.bcx.build_config.build_plan {
+        Job::new(Work::noop(), Freshness::Dirty)
+    } else {
+        fingerprint::prepare_target(cx, unit, false)?
+    };
+    if job.freshness() == Freshness::Dirty {
+        job.before(dirty);
+    } else {
+        job.before(fresh);
+    }
+    Ok(job)
 }
 
 impl BuildState {
@@ -637,22 +632,20 @@ pub fn build_map<'b, 'cfg>(cx: &mut Context<'b, 'cfg>, units: &[Unit<'b>]) -> Ca
             return Ok(&out[unit]);
         }
 
-        {
-            let key = unit
-                .pkg
-                .manifest()
-                .links()
-                .map(|l| (l.to_string(), unit.kind));
-            let build_state = &cx.build_state;
-            if let Some(output) = key.and_then(|k| build_state.overrides.get(&k)) {
-                let key = (unit.pkg.package_id(), unit.kind);
-                cx.build_script_overridden.insert(key);
-                build_state
-                    .outputs
-                    .lock()
-                    .unwrap()
-                    .insert(key, output.clone());
-            }
+        let key = unit
+            .pkg
+            .manifest()
+            .links()
+            .map(|l| (l.to_string(), unit.kind));
+        let build_state = &cx.build_state;
+        if let Some(output) = key.and_then(|k| build_state.overrides.get(&k)) {
+            let key = (unit.pkg.package_id(), unit.kind);
+            cx.build_script_overridden.insert(key);
+            build_state
+                .outputs
+                .lock()
+                .unwrap()
+                .insert(key, output.clone());
         }
 
         let mut ret = BuildScripts::default();
@@ -661,6 +654,10 @@ pub fn build_map<'b, 'cfg>(cx: &mut Context<'b, 'cfg>, units: &[Unit<'b>]) -> Ca
             add_to_link(&mut ret, unit.pkg.package_id(), unit.kind);
         }
 
+        if unit.mode.is_run_custom_build() {
+            parse_previous_explicit_deps(cx, unit)?;
+        }
+
         // We want to invoke the compiler deterministically to be cache-friendly
         // to rustc invocation caching schemes, so be sure to generate the same
         // set of build script dependency orderings via sorting the targets that
@@ -694,4 +691,29 @@ pub fn build_map<'b, 'cfg>(cx: &mut Context<'b, 'cfg>, units: &[Unit<'b>]) -> Ca
             scripts.to_link.push((pkg, kind));
         }
     }
+
+    fn parse_previous_explicit_deps<'a, 'cfg>(cx: &mut Context<'a, 'cfg>, unit: &Unit<'a>) -> CargoResult<()> {
+        let script_out_dir = cx.files().build_script_out_dir(unit);
+        let script_run_dir = cx.files().build_script_run_dir(unit);
+        let root_output_file = script_run_dir.join("root-output");
+        let output_file = script_run_dir.join("output");
+
+        // Check to see if the build script has already run, and if it has, keep
+        // track of whether it has told us about some explicit dependencies.
+        let prev_script_out_dir = paths::read_bytes(&root_output_file)
+            .and_then(|bytes| util::bytes2path(&bytes))
+            .unwrap_or_else(|_| script_out_dir.clone());
+
+        let prev_output = BuildOutput::parse_file(
+            &output_file,
+            &unit.pkg.to_string(),
+            &prev_script_out_dir,
+            &script_out_dir,
+        )
+        .ok();
+
+        let deps = BuildDeps::new(&output_file, prev_output.as_ref());
+        cx.build_explicit_deps.insert(*unit, deps);
+        Ok(())
+    }
 }