Fix a flaky test relying on nondeterminsm

When updating a source with multiple packages, the registry will lazily discover
both the precise and imprecise versions of the source at some point. Previously
the source would be updated depending on which was discovered first, but this
commit adds logic to understand that if an imprecise version is discovered after
a precise version then the imprecise version should be favored (because it will
always trigger an update).

This needs to understand, however, that if `cargo update --precise` is used that
those sources should not be updated again, so the sources treated in
`add_sources` are considered "special" in the sense that they're locked and will
not be updated again.

src/cargo/core/registry.rs

@@ -41,13 +41,39 @@ pub struct PackageRegistry<'a> {
     // A list of sources which are considered "overrides" which take precedent
     // when querying for packages.
     overrides: Vec<SourceId>,
+
+    // Note that each SourceId does not take into account its `precise` field
+    // when hashing or testing for equality. When adding a new `SourceId`, we
+    // want to avoid duplicates in the `SourceMap` (to prevent re-updating the
+    // same git repo twice for example), but we also want to ensure that the
+    // loaded source is always updated.
+    //
+    // Sources with a `precise` field normally don't need to be updated because
+    // their contents are already on disk, but sources without a `precise` field
+    // almost always need to be updated. If we have a cached `Source` for a
+    // precise `SourceId`, then when we add a new `SourceId` that is not precise
+    // we want to ensure that the underlying source is updated.
+    //
+    // This is basically a long-winded way of saying that we want to know
+    // precisely what the keys of `sources` are, so this is a mapping of key to
+    // what exactly the key is.
+    source_ids: HashMap<SourceId, (SourceId, Kind)>,
+
     locked: HashMap<SourceId, HashMap<String, Vec<(PackageId, Vec<PackageId>)>>>,
 }
 
+#[deriving(PartialEq, Eq)]
+enum Kind {
+    Override,
+    Locked,
+    Normal,
+}
+
 impl<'a> PackageRegistry<'a> {
     pub fn new<'a>(config: &'a mut Config<'a>) -> PackageRegistry<'a> {
         PackageRegistry {
             sources: SourceMap::new(),
+            source_ids: HashMap::new(),
             overrides: vec!(),
             config: config,
             locked: HashMap::new(),
@@ -82,22 +108,43 @@ impl<'a> PackageRegistry<'a> {
     }
 
     fn ensure_loaded(&mut self, namespace: &SourceId) -> CargoResult<()> {
-        if self.sources.contains(namespace) { return Ok(()); }
+        match self.source_ids.find(namespace) {
+            // We've previously loaded this source, and we've already locked it,
+            // so we're not allowed to change it even if `namespace` has a
+            // slightly different precise version listed.
+            Some(&(_, Locked)) => return Ok(()),
 
-        try!(self.load(namespace, false));
+            // If the previous source was not a precise source, then we can be
+            // sure that it's already been updated if we've already loaded it.
+            Some(&(ref previous, _)) if previous.get_precise().is_none() => {
+                return Ok(())
+            }
+
+            // If the previous source has the same precise version as we do,
+            // then we're done, otherwise we need to need to move forward
+            // updating this source.
+            Some(&(ref previous, _)) => {
+                if previous.get_precise() == namespace.get_precise() {
+                    return Ok(())
+                }
+            }
+            None => {}
+        }
+
+        try!(self.load(namespace, Normal));
         Ok(())
     }
 
     pub fn add_sources(&mut self, ids: &[SourceId]) -> CargoResult<()> {
         for id in ids.iter() {
-            try!(self.load(id, false));
+            try!(self.load(id, Locked));
         }
         Ok(())
     }
 
     pub fn add_overrides(&mut self, ids: Vec<SourceId>) -> CargoResult<()> {
         for id in ids.iter() {
-            try!(self.load(id, true));
+            try!(self.load(id, Override));
         }
         Ok(())
     }
@@ -114,7 +161,7 @@ impl<'a> PackageRegistry<'a> {
         sub_vec.push((id, deps));
     }
 
-    fn load(&mut self, source_id: &SourceId, is_override: bool) -> CargoResult<()> {
+    fn load(&mut self, source_id: &SourceId, kind: Kind) -> CargoResult<()> {
         (|| {
             let mut source = source_id.load(self.config);
 
@@ -123,12 +170,13 @@ impl<'a> PackageRegistry<'a> {
             try!(source.update());
             drop(p);
 
-            if is_override {
+            if kind == Override {
                 self.overrides.push(source_id.clone());
             }
 
             // Save off the source
             self.sources.insert(source_id, source);
+            self.source_ids.insert(source_id.clone(), (source_id.clone(), kind));
 
             Ok(())
         }).chain_error(|| human(format!("Unable to update {}", source_id)))

tests/test_cargo_compile_git_deps.rs

@@ -696,16 +696,19 @@ test!(update_with_shared_deps {
     timer::sleep(Duration::milliseconds(1000));
 
     // By default, not transitive updates
+    println!("dep1 update");
     assert_that(p.process(cargo_dir().join("cargo")).arg("update").arg("dep1"),
                 execs().with_stdout(""));
 
     // Specifying a precise rev to the old rev shouldn't actually update
     // anything because we already have the rev in the db.
+    println!("bar precise update");
     assert_that(p.process(cargo_dir().join("cargo")).arg("update").arg("bar")
                  .arg("--precise").arg(old_head.to_string()),
                 execs().with_stdout(""));
 
     // Updating aggressively should, however, update the repo.
+    println!("dep1 aggressive update");
     assert_that(p.process(cargo_dir().join("cargo")).arg("update").arg("dep1")
                  .arg("--aggressive"),
                 execs().with_stdout(format!("{} git repository `{}`",
@@ -713,6 +716,7 @@ test!(update_with_shared_deps {
                                             git_project.url())));
 
     // Make sure we still only compile one version of the git repo
+    println!("build");
     assert_that(p.process(cargo_dir().join("cargo")).arg("build"),
                 execs().with_stdout(format!("\
 {compiling} bar v0.5.0 ({git}#[..])