Partially revert dep changes in #5651

Some logic which was tweaked around the dependencies of build script targets was
tweaked slightly in a way that causes cargo to stack overflow by accientally
adding a dependency loop. This commit implements one of the strategies discussed
in #5711 to fix this situation.

The problem here is that when calculating the deps of a build script we need the
build scripts of *other* packages, but the exact profile is somewhat difficult
to guess at the moment we're generating our build script unit. To solve this the
dependencies towards other build scripts' executions is added in a different
pass after all other units have been assembled. At this point we should know for
sure that all build script executions are in the dependency graph, and we just
need to add a few more edges.

Closes #5708

Author: alexcrichton

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

@@ -15,7 +15,7 @@
 //! (for example, with and without tests), so we actually build a dependency
 //! graph of `Unit`s, which capture these properties.
 
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 
 use CargoResult;
 use core::dependency::Kind as DepKind;
@@ -26,8 +26,10 @@ use super::{BuildContext, CompileMode, Kind, Unit};
 pub fn build_unit_dependencies<'a, 'cfg>(
     roots: &[Unit<'a>],
     bcx: &BuildContext<'a, 'cfg>,
-    mut deps: &mut HashMap<Unit<'a>, Vec<Unit<'a>>>,
+    deps: &mut HashMap<Unit<'a>, Vec<Unit<'a>>>,
 ) -> CargoResult<()> {
+    assert!(deps.len() == 0, "can only build unit deps once");
+
     for unit in roots.iter() {
         // Dependencies of tests/benches should not have `panic` set.
         // We check the global test mode to see if we are running in `cargo
@@ -40,34 +42,36 @@ pub fn build_unit_dependencies<'a, 'cfg>(
         } else {
             ProfileFor::Any
         };
-        deps_of(unit, bcx, &mut deps, profile_for)?;
+        deps_of(unit, bcx, deps, profile_for)?;
     }
     trace!("ALL UNIT DEPENDENCIES {:#?}", deps);
 
+    connect_run_custom_build_deps(bcx, deps);
+
     Ok(())
 }
 
-fn deps_of<'a, 'b, 'cfg>(
+fn deps_of<'a, 'cfg>(
     unit: &Unit<'a>,
     bcx: &BuildContext<'a, 'cfg>,
-    deps: &'b mut HashMap<Unit<'a>, Vec<Unit<'a>>>,
+    deps: &mut HashMap<Unit<'a>, Vec<Unit<'a>>>,
     profile_for: ProfileFor,
-) -> CargoResult<&'b [Unit<'a>]> {
+) -> CargoResult<()> {
     // Currently the `deps` map does not include `profile_for`.  This should
     // be safe for now.  `TestDependency` only exists to clear the `panic`
     // flag, and you'll never ask for a `unit` with `panic` set as a
     // `TestDependency`.  `CustomBuild` should also be fine since if the
     // requested unit's settings are the same as `Any`, `CustomBuild` can't
     // affect anything else in the hierarchy.
     if !deps.contains_key(unit) {
-        let unit_deps = compute_deps(unit, bcx, deps, profile_for)?;
+        let unit_deps = compute_deps(unit, bcx, profile_for)?;
         let to_insert: Vec<_> = unit_deps.iter().map(|&(unit, _)| unit).collect();
         deps.insert(*unit, to_insert);
         for (unit, profile_for) in unit_deps {
             deps_of(&unit, bcx, deps, profile_for)?;
         }
     }
-    Ok(deps[unit].as_ref())
+    Ok(())
 }
 
 /// For a package, return all targets which are registered as dependencies
@@ -77,11 +81,10 @@ fn deps_of<'a, 'b, 'cfg>(
 fn compute_deps<'a, 'b, 'cfg>(
     unit: &Unit<'a>,
     bcx: &BuildContext<'a, 'cfg>,
-    deps: &'b mut HashMap<Unit<'a>, Vec<Unit<'a>>>,
     profile_for: ProfileFor,
 ) -> CargoResult<Vec<(Unit<'a>, ProfileFor)>> {
     if unit.mode.is_run_custom_build() {
-        return compute_deps_custom_build(unit, bcx, deps);
+        return compute_deps_custom_build(unit, bcx);
     } else if unit.mode.is_doc() && !unit.mode.is_any_test() {
         // Note: This does not include Doctest.
         return compute_deps_doc(unit, bcx);
@@ -194,39 +197,27 @@ fn compute_deps<'a, 'b, 'cfg>(
 fn compute_deps_custom_build<'a, 'cfg>(
     unit: &Unit<'a>,
     bcx: &BuildContext<'a, 'cfg>,
-    deps: &mut HashMap<Unit<'a>, Vec<Unit<'a>>>,
 ) -> CargoResult<Vec<(Unit<'a>, ProfileFor)>> {
     // When not overridden, then the dependencies to run a build script are:
     //
     // 1. Compiling the build script itself
     // 2. For each immediate dependency of our package which has a `links`
     //    key, the execution of that build script.
-    let deps = deps
-        .iter()
-        .find(|(key, _deps)| key.pkg == unit.pkg && !key.target.is_custom_build())
-        .expect("can't find package deps")
-        .1;
-    Ok(deps.iter()
-        .filter_map(|unit| {
-            if !unit.target.linkable() || unit.pkg.manifest().links().is_none() {
-                return None;
-            }
-            dep_build_script(unit, bcx)
-        })
-        .chain(Some((
-            new_unit(
-                bcx,
-                unit.pkg,
-                unit.target,
-                ProfileFor::CustomBuild,
-                Kind::Host, // build scripts always compiled for the host
-                CompileMode::Build,
-            ),
-            // All dependencies of this unit should use profiles for custom
-            // builds.
-            ProfileFor::CustomBuild,
-        )))
-        .collect())
+    //
+    // We don't have a great way of handling (2) here right now so this is
+    // deferred until after the graph of all unit dependencies has been
+    // constructed.
+    let unit = new_unit(
+        bcx,
+        unit.pkg,
+        unit.target,
+        ProfileFor::CustomBuild,
+        Kind::Host, // build scripts always compiled for the host
+        CompileMode::Build,
+    );
+    // All dependencies of this unit should use profiles for custom
+    // builds.
+    Ok(vec![(unit, ProfileFor::CustomBuild)])
 }
 
 /// Returns the dependencies necessary to document a package
@@ -371,3 +362,74 @@ fn new_unit<'a>(
         mode,
     }
 }
+
+/// Fill in missing dependencies for units of the `RunCustomBuild`
+///
+/// As mentioned above in `compute_deps_custom_build` each build script
+/// execution has two dependencies. The first is compiling the build script
+/// itself (already added) and the second is that all crates the package of the
+/// build script depends on with `links` keys, their build script execution. (a
+/// bit confusing eh?)
+///
+/// Here we take the entire `deps` map and add more dependencies from execution
+/// of one build script to execution of another build script.
+fn connect_run_custom_build_deps<'a>(
+    bcx: &BuildContext,
+    deps: &mut HashMap<Unit<'a>, Vec<Unit<'a>>>,
+) {
+    let mut new_deps = Vec::new();
+
+    {
+        // First up build a reverse dependency map. This is a mapping of all
+        // `RunCustomBuild` known steps to the unit which depends on them. For
+        // example a library might depend on a build script, so this map will
+        // have the build script as the key and the library would be in the
+        // value's set.
+        let mut reverse_deps = HashMap::new();
+        for (unit, deps) in deps.iter() {
+            for dep in deps {
+                if dep.mode == CompileMode::RunCustomBuild {
+                    reverse_deps.entry(dep)
+                        .or_insert(HashSet::new())
+                        .insert(unit);
+                }
+            }
+        }
+
+        // And next we take a look at all build scripts executions listed in the
+        // dependency map. Our job here is to take everything that depends on
+        // this build script (from our reverse map above) and look at the other
+        // package dependencies of these parents.
+        //
+        // If we depend on a linkable target and the build script mentions
+        // `links`, then we depend on that package's build script! Here we use
+        // `dep_build_script` to manufacture an appropriate build script unit to
+        // depend on.
+        for unit in deps.keys().filter(|k| k.mode == CompileMode::RunCustomBuild) {
+            let reverse_deps = match reverse_deps.get(unit) {
+                Some(set) => set,
+                None => continue,
+            };
+
+            let to_add = reverse_deps
+                .iter()
+                .flat_map(|reverse_dep| deps[reverse_dep].iter())
+                .filter(|other| {
+                    other.pkg != unit.pkg &&
+                        other.target.linkable() &&
+                        other.pkg.manifest().links().is_some()
+                })
+                .filter_map(|other| dep_build_script(other, bcx).map(|p| p.0))
+                .collect::<HashSet<_>>();
+
+            if !to_add.is_empty() {
+                new_deps.push((*unit, to_add));
+            }
+        }
+    }
+
+    // And finally, add in all the missing dependencies!
+    for (unit, new_deps) in new_deps {
+        deps.get_mut(&unit).unwrap().extend(new_deps);
+    }
+}

tests/testsuite/build_script.rs

@@ -3080,9 +3080,11 @@ fn panic_abort_with_build_scripts() {
         execs().with_status(0),
     );
 
+    p.root().join("target").rm_rf();
+
     assert_that(
-        p.cargo("test --release"),
-        execs().with_status(0)
+        p.cargo("test --release -v"),
+        execs().with_status(0).with_stderr_does_not_contain("[..]panic[..]"),
     );
 }
 

tests/testsuite/test.rs

@@ -4138,3 +4138,28 @@ fn json_artifact_includes_test_flag() {
         ),
     );
 }
+
+#[test]
+fn test_build_script_links() {
+    let p = project("foo")
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.0.1"
+                links = 'something'
+
+                [lib]
+                test = false
+            "#,
+        )
+        .file("build.rs", "fn main() {}")
+        .file("src/lib.rs", "")
+        .build();
+
+    assert_that(
+        p.cargo("test --no-run"),
+        execs().with_status(0),
+    );
+}