cargo: make filenames predictable

source_id changes based on innocuous things like the path of the work
directory.  This breaks sstate badly, because two builds with the same
inputs will produce different, incompatible outputs.  Removing source_id
from the hash calculation makes the value stable enough for sstate.

Author: srwalter

recipes-devtools/cargo/cargo.inc

@@ -10,6 +10,7 @@ DEPENDS = "openssl zlib libgit2 curl ca-certificates libssh2"
 
 SRC_URI = "\
 	http://static-rust-lang-org.s3.amazonaws.com/cargo-dist/${CARGO_SNAPSHOT} \
+	file://0001-Don-t-hash-source_id.patch \
 "
 
 B = "${S}"

recipes-devtools/cargo/cargo/0001-Don-t-hash-source_id.patch

@@ -0,0 +1,27 @@
+From a65784be8fdbc7dffa6d568bcc364cb67655ebfe Mon Sep 17 00:00:00 2001
+From: Steven Walter <[email protected]>
+Date: Fri, 27 Jan 2017 11:24:57 -0500
+Subject: [PATCH] Don't hash source_id
+
+This makes hashes reproducible when building directly in the source as
+well as from a registry. Reproducible file names are necessary for
+linking against externally built crates.
+---
+ src/cargo/core/package_id.rs | 1 -
+ 1 file changed, 1 deletion(-)
+
+diff --git a/src/cargo/core/package_id.rs b/src/cargo/core/package_id.rs
+index b29b8ca..7691d38 100644
+--- a/src/cargo/core/package_id.rs
++++ b/src/cargo/core/package_id.rs
+@@ -66,7 +66,6 @@ impl Hash for PackageId {
+     fn hash<S: hash::Hasher>(&self, state: &mut S) {
+         self.inner.name.hash(state);
+         self.inner.version.hash(state);
+-        self.inner.source_id.hash(state);
+     }
+ }
+ 
+-- 
+2.7.4
+