Supply crate metadata to rustc and uniqueify --extern'ed crates

rust/rust.bzl

@@ -198,7 +198,10 @@ def _find_crate_root_src(srcs, file_names=["lib.rs"]):
       return src
   fail("No %s source file found." % " or ".join(file_names), "srcs")
 
-def _determine_lib_name(name, crate_type, toolchain):
+def _determine_output_hash(lib_rs):
+  return repr(hash(lib_rs.path))
+
+def _determine_lib_name(name, crate_type, toolchain, lib_hash=""):
   extension = None
   if crate_type in ("dylib", "cdylib", "proc-macro"):
     extension = toolchain.dylib_ext
@@ -216,8 +219,9 @@ def _determine_lib_name(name, crate_type, toolchain):
          + "please file an issue!") % crate_type)
 
 
-  return "lib{name}{extension}".format(name=name,
-                                       extension=extension)
+  return "lib{name}-{lib_hash}{extension}".format(name=name,
+                                                  lib_hash=lib_hash,
+                                                  extension=extension)
 
 def _crate_root_src(ctx, file_names=["lib.rs"]):
   if ctx.file.crate_root == None:
@@ -236,10 +240,14 @@ def _rust_library_impl(ctx):
   # Find toolchain
   toolchain = _find_toolchain(ctx)
 
+  # Determine unique hash for this rlib
+  output_hash = _determine_output_hash(lib_rs);
+
   # Output library
   rust_lib_name = _determine_lib_name(ctx.attr.name,
                                       ctx.attr.crate_type,
-                                      toolchain);
+                                      toolchain,
+                                      output_hash)
   rust_lib = ctx.actions.declare_file(rust_lib_name)
   output_dir = rust_lib.dirname
 
@@ -257,6 +265,7 @@ def _rust_library_impl(ctx):
       crate_type = ctx.attr.crate_type,
       src = lib_rs,
       output_dir = output_dir,
+      output_hash = output_hash,
       depinfo = depinfo)
 
   # Compile action.

rust/toolchain.bzl

@@ -6,7 +6,7 @@ ZIP_PATH = "/usr/bin/zip"
 
 # Utility methods that use the toolchain provider.
 def build_rustc_command(ctx, toolchain, crate_name, crate_type, src, output_dir,
-                         depinfo, rust_flags=[]):
+                         depinfo, output_hash=None, rust_flags=[]):
   """
   Constructs the rustc command used to build the current target.
   """
@@ -26,6 +26,10 @@ def build_rustc_command(ctx, toolchain, crate_name, crate_type, src, output_dir,
   # Construct features flags
   features_flags = _get_features_flags(ctx.attr.crate_features)
 
+  extra_filename = ""
+  if output_hash:
+    extra_filename = "-%s" % output_hash
+
   return " ".join(
       ["set -e;"] +
       depinfo.setup_cmd +
@@ -37,6 +41,9 @@ def build_rustc_command(ctx, toolchain, crate_name, crate_type, src, output_dir,
           "--crate-name %s" % crate_name,
           "--crate-type %s" % crate_type,
           "-C opt-level=3",
+          # Disambiguate this crate from similarly named ones
+          "-C metadata=%s" % extra_filename,
+          "-C extra-filename='%s'" % extra_filename,
           "--codegen ar=%s" % ar,
           "--codegen linker=%s" % cc,
           "--codegen link-args='%s'" % ' '.join(cpp_fragment.link_options),

test/BUILD

@@ -12,11 +12,11 @@ load(
 )
 
 rule_test(
-    name ="hello_lib_rule_test",
-    generates = ["libhello_lib.rlib"],
+    name = "hello_lib_rule_test",
+    generates = ["libhello_lib--1343350674.rlib"],
     provides = {
-        "rust_lib": "/libhello_lib.rlib>\\?$",
-        "transitive_libs": "^\\[\\]$"
+        "rust_lib": "/libhello_lib--1343350674.rlib>\\?$",
+        "transitive_libs": "^\\[\\]$",
     },
     rule = "@examples//hello_lib:hello_lib",
 )
@@ -29,7 +29,6 @@ rule_test(
 
 rule_test(
     name = "greeting_rule_test",
-    generates = ["libhello_lib.rlib"],
+    generates = ["libhello_lib--1343350674.rlib"],
     rule = "@examples//hello_lib:hello_lib",
 )
-

test/conflicting_deps/BUILD

@@ -0,0 +1,22 @@
+package(default_visibility = ["//visibility:public"])
+
+load(
+    "//rust:rust.bzl",
+    "rust_library",
+    "rust_test",
+)
+
+rust_library(
+    name = "conflicting_deps",
+    srcs = ["src/lib.rs"],
+    deps = [
+        "//test/conflicting_deps/first_crate:example_name_conflict"
+    ],
+)
+
+rust_test(
+    name = "conflicting_deps_test",
+    deps = [
+        ":conflicting_deps",
+    ],
+)

test/conflicting_deps/first_crate/BUILD

@@ -0,0 +1,15 @@
+package(default_visibility = ["//visibility:public"])
+
+load(
+    "//rust:rust.bzl",
+    "rust_library",
+)
+
+rust_library(
+    name = "example_name_conflict",
+    srcs = ["src/lib.rs"],
+    deps = [
+        "//test/conflicting_deps/first_crate/second_crate:example_name_conflict"
+    ],
+)
+

test/conflicting_deps/first_crate/second_crate/BUILD

@@ -0,0 +1,12 @@
+package(default_visibility = ["//visibility:public"])
+
+load(
+    "//rust:rust.bzl",
+    "rust_library",
+)
+
+rust_library(
+    name = "example_name_conflict",
+    srcs = ["src/lib.rs"],
+    deps = [],
+)

test/conflicting_deps/first_crate/second_crate/src/lib.rs

@@ -0,0 +1,5 @@
+// This crate's name conflicts with its dependent but this should work OK.
+
+pub fn example_conflicting_symbol() -> String {
+    "[from second_crate]".to_owned()
+}

test/conflicting_deps/first_crate/src/lib.rs

@@ -0,0 +1,10 @@
+// This crate's name conflicts with its dependency but this should work OK.
+
+extern crate example_name_conflict;
+
+pub fn example_conflicting_symbol() -> String {
+    format!(
+        "[from first_crate] -> {}",
+        example_name_conflict::example_conflicting_symbol()
+    )
+}

test/conflicting_deps/src/lib.rs

@@ -0,0 +1,22 @@
+extern crate example_name_conflict;
+
+// This crate depends on a pair of dependencies (transitively) that have the same name. This should
+// work OK.
+
+pub fn example_conflicting_symbol() -> String {
+    format!(
+        "[from main lib] -> {}",
+        example_name_conflict::example_conflicting_symbol()
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn symbols_all_resolve_correctly() {
+        assert_eq!(
+            ::example_conflicting_symbol(),
+            "[from main lib] -> [from first_crate] -> [from second_crate]".to_owned()
+        );
+    }
+}