Fix support for crate_type w.r.t. output file extension

examples/hello_lib/BUILD

@@ -16,6 +16,15 @@ rust_library(
     ],
 )
 
+rust_library(
+    name = "hello_dylib",
+    srcs = [
+        "src/greeter.rs",
+        "src/lib.rs",
+    ],
+    crate_type = "dylib",
+)
+
 rust_test(
     name = "hello_lib_test",
     deps = [":hello_lib"],

rust/rust.bzl

@@ -60,6 +60,27 @@ LIBRARY_CRATE_TYPES = [
     "staticlib",
 ]
 
+LIBRARY_AND_PLATFORM_TO_EXTENSION = {
+    ("dylib", "linux"): ".so",
+    ("dylib", "darwin"): ".dylib",
+    ("dylib", "windows"): ".dll",
+    ("cdylib", "linux"): ".so",
+    ("cdylib", "darwin"): ".dylib",
+    ("cdylib", "windows"): ".dll",
+    ("staticlib", "linux"): ".a",
+    ("staticlib", "darwin"): ".a",
+    ("staticlib", "windows"): ".lib",
+    ("bin", "linux"): "",
+    ("bin", "darwin"): "",
+    ("bin", "windows"): ".exe",
+    ("lib", "linux"): ".rlib",
+    ("lib", "darwin"): ".rlib",
+    ("lib", "windows"): ".rlib",
+    ("rlib", "linux"): ".rlib",
+    ("rlib", "darwin"): ".rlib",
+    ("rlib", "windows"): ".rlib",
+}
+
 # Used by rust_doc
 HTML_MD_FILETYPE = FileType([
     ".html",
@@ -203,6 +224,20 @@ def _get_features_flags(features):
     features_flags += ["--cfg feature=\\\"%s\\\"" % feature]
   return features_flags
 
+def _get_crate_type_and_target_outputs(name, crate_type, platform):
+  crate_type = crate_type or "rlib"
+  platform = platform or "linux"
+  extension = LIBRARY_AND_PLATFORM_TO_EXTENSION[crate_type, platform]
+
+  if crate_type == "bin":
+    return {
+        "rust_lib": "%{{name}}{}".format(extension)
+    }
+  else:
+    return {
+        "rust_lib": "lib%{{name}}{}".format(extension)
+    }
+
 def _get_dirname(short_path):
   return short_path[0:short_path.rfind('/')]
 
@@ -659,12 +694,13 @@ _rust_toolchain_attrs = {
         single_file = True,
     ),
     "_crosstool": attr.label(
-        default = Label("//tools/defaults:crosstool")
+        default = Label("//tools/defaults:crosstool"),
     ),
 }
 
 _rust_library_attrs = {
     "crate_type": attr.string(),
+    "platform": attr.string(),
 }
 
 rust_library = rule(
@@ -673,10 +709,9 @@ rust_library = rule(
                  _rust_library_attrs.items() +
                  _rust_toolchain_attrs.items()),
     fragments = ["cpp"],
-    outputs = {
-        "rust_lib": "lib%{name}.rlib",
-    },
+    outputs = _get_crate_type_and_target_outputs,
 )
+
 """Builds a Rust library crate.
 
 Args:
@@ -781,6 +816,7 @@ rust_binary = rule(
     executable = True,
     fragments = ["cpp"],
 )
+
 """Builds a Rust binary crate.
 
 Args:
@@ -905,6 +941,7 @@ rust_test = rule(
     fragments = ["cpp"],
     test = True,
 )
+
 """Builds a Rust test crate.
 
 Args:
@@ -1067,6 +1104,7 @@ rust_bench_test = rule(
     fragments = ["cpp"],
     test = True,
 )
+
 """Builds a Rust benchmark test.
 
 **Warning**: This rule is currently experimental. [Rust Benchmark
@@ -1200,6 +1238,7 @@ rust_doc = rule(
         "rust_doc_zip": "%{name}-docs.zip",
     },
 )
+
 """Generates code documentation.
 
 Args:
@@ -1258,6 +1297,7 @@ rust_doc_test = rule(
     executable = True,
     test = True,
 )
+
 """Runs Rust documentation tests.
 
 Args: