Auto merge of #4239 - Keruspe:master, r=alexcrichton

hash '__CARGO_DEFAULT_LIB_METADATA' in metadata for rustc

We already have __CARGO_DEFAULT_LIB_METADATA to force adding the hash of some metadata in the libraries file name when building rust.
For now, we only check if it is set or not.
This patch makes also use of its value to compute the hash. This way we'll be able to pass in the channel we're building to avoid hash collisions between channels.

Author: bors

src/cargo/ops/cargo_rustc/context.rs

@@ -442,16 +442,17 @@ impl<'a, 'cfg> Context<'a, 'cfg> {
         // Note, though, that the compiler's build system at least wants
         // path dependencies (eg libstd) to have hashes in filenames. To account for
         // that we have an extra hack here which reads the
-        // `__CARGO_DEFAULT_METADATA` environment variable and creates a
+        // `__CARGO_DEFAULT_LIB_METADATA` environment variable and creates a
         // hash in the filename if that's present.
         //
         // This environment variable should not be relied on! It's
         // just here for rustbuild. We need a more principled method
         // doing this eventually.
+        let __cargo_default_lib_metadata = env::var("__CARGO_DEFAULT_LIB_METADATA");
         if !unit.profile.test &&
             (unit.target.is_dylib() || unit.target.is_cdylib()) &&
             unit.pkg.package_id().source_id().is_path() &&
-            !env::var("__CARGO_DEFAULT_LIB_METADATA").is_ok() {
+            !__cargo_default_lib_metadata.is_ok() {
             return None;
         }
 
@@ -491,6 +492,12 @@ impl<'a, 'cfg> Context<'a, 'cfg> {
             rustc.verbose_version.hash(&mut hasher);
         }
 
+        // Seed the contents of __CARGO_DEFAULT_LIB_METADATA to the hasher if present.
+        // This should be the release channel, to get a different hash for each channel.
+        if let Ok(ref channel) = __cargo_default_lib_metadata {
+            channel.hash(&mut hasher);
+        }
+
         Some(Metadata(hasher.finish()))
     }
 

tests/build.rs

@@ -859,7 +859,7 @@ suffix = env::consts::DLL_SUFFIX,
     assert_that(p.cargo("clean"), execs().with_status(0));
 
     // If you set the env-var, then we expect metadata on libbar
-    assert_that(p.cargo("build").arg("-v").env("__CARGO_DEFAULT_LIB_METADATA", "1"),
+    assert_that(p.cargo("build").arg("-v").env("__CARGO_DEFAULT_LIB_METADATA", "stable"),
                 execs().with_status(0).with_stderr(&format!("\
 [COMPILING] bar v0.0.1 ({url}/bar)
 [RUNNING] `rustc --crate-name bar bar[/]src[/]lib.rs --crate-type dylib \