Look for ${crate_name}.rs as a crate_root by default. (bazelbuild#137)

README.md

@@ -94,7 +94,7 @@ rust_library(name, srcs, crate_root, crate_type, deps, data, crate_features, rus
         library.</p>
         <p>
           If <code>srcs</code> contains more than one file, then there must be
-          a file either named <code>lib.rs</code>. Otherwise,
+          a file either named <code>lib.rs</code> or <code>${name}.rs</code>. Otherwise,
           <code>crate_root</code> must be set to the source file that is the
           root of the crate to be passed to <code>rustc</code> to build this
           crate.
@@ -111,8 +111,8 @@ rust_library(name, srcs, crate_root, crate_type, deps, data, crate_features, rus
         </p>
         <p>
           If <code>crate_root</code> is not set, then this rule will look for
-          a <code>lib.rs</code> file or the single file in <code>srcs</code>
-          if <code>srcs</code> contains only one file.
+          a <code>lib.rs</code> file, or the single file in <code>srcs</code>
+          if <code>srcs</code> contains only one file, or a <code>${name}.rs</code> file.
         </p>
       </td>
     </tr>
@@ -302,7 +302,7 @@ rust_binary(name, srcs, deps, data, crate_features, rustc_flags, version, out_di
         binary.</p>
         <p>
           If <code>srcs</code> contains more than one file, then there must be
-          a file either named <code>main.rs</code>. Otherwise,
+          a file either named <code>main.rs</code> or <code>${name}.rs</code>. Otherwise,
           <code>crate_root</code> must be set to the source file that is the
           root of the crate to be passed to <code>rustc</code> to build this
           crate.
@@ -319,8 +319,8 @@ rust_binary(name, srcs, deps, data, crate_features, rustc_flags, version, out_di
         </p>
         <p>
           If <code>crate_root</code> is not set, then this rule will look for
-          a <code>main.rs</code> file or the single file in <code>srcs</code>
-          if <code>srcs</code> contains only one file.
+          a <code>main.rs</code> file, or the single file in <code>srcs</code>
+          if <code>srcs</code> contains only one file, or a <code>${name}.rs</code> file.
         </p>
       </td>
     </td>
@@ -512,7 +512,7 @@ rust_test(name, srcs, deps, data, crate_features, rustc_flags, version, out_dir_
         library.</p>
         <p>
           If <code>srcs</code> contains more than one file, then there must be
-          a file either named <code>lib.rs</code>. Otherwise,
+          a file either named <code>lib.rs</code> or <code>${name}.rs</code>. Otherwise,
           <code>crate_root</code> must be set to the source file that is the
           root of the crate to be passed to <code>rustc</code> to build this
           crate.
@@ -529,8 +529,8 @@ rust_test(name, srcs, deps, data, crate_features, rustc_flags, version, out_dir_
         </p>
         <p>
           If <code>crate_root</code> is not set, then this rule will look for
-          a <code>lib.rs</code> file or the single file in <code>srcs</code>
-          if <code>srcs</code> contains only one file.
+          a <code>lib.rs</code> file, or the single file in <code>srcs</code>
+          if <code>srcs</code> contains only one file, or a <code>${name}.rs</code> file.
         </p>
       </td>
     </td>
@@ -728,7 +728,7 @@ rust_test(
 Run the test with `bazel build //hello_lib:hello_lib_test`.
 
 <a name="rust_benchmark"></a>
-## rust\_bench\_test
+## rust\_benchmark
 
 ```python
 rust_benchmark(name, srcs, deps, data, crate_features, rustc_flags, out_dir_tar)
@@ -773,7 +773,7 @@ easy to use a custom Rust toolchain, such as a nightly release.
         library.</p>
         <p>
           If <code>srcs</code> contains more than one file, then there must be
-          a file either named <code>lib.rs</code>. Otherwise,
+          a file either named <code>lib.rs</code> or <code>${name}.rs</code>. Otherwise,
           <code>crate_root</code> must be set to the source file that is the
           root of the crate to be passed to <code>rustc</code> to build this
           crate.
@@ -790,8 +790,8 @@ easy to use a custom Rust toolchain, such as a nightly release.
         </p>
         <p>
           If <code>crate_root</code> is not set, then this rule will look for
-          a <code>lib.rs</code> file or the single file in <code>srcs</code>
-          if <code>srcs</code> contains only one file.
+          a <code>lib.rs</code> file, or the single file in <code>srcs</code>
+          if <code>srcs</code> contains only one file, or a <code>${name}.rs</code> file.
         </p>
       </td>
     </td>

examples/ffi/rust_calling_c/BUILD

@@ -6,7 +6,6 @@ rust_library(
     name = "matrix",
     srcs = [
         "src/ffi.rs",
-        "src/lib.rs",
         "src/matrix.rs",
     ],
     deps = [
@@ -31,9 +30,9 @@ rust_library(
     name = "matrix_dynamically_linked",
     srcs = [
         "src/ffi.rs",
-        "src/lib.rs",
         "src/matrix.rs",
     ],
+    crate_root = "src/matrix.rs",
     deps = [
         "//ffi/rust_calling_c/c:native_matrix_so",
         "@libc",

examples/ffi/rust_calling_c/src/matrix.rs

@@ -12,7 +12,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use ffi;
+extern crate libc;
+
+mod ffi;
+
 use std::ops;
 use std::ptr;
 

rust/private/rust.bzl

@@ -15,15 +15,6 @@
 load(":private/rustc.bzl", "CrateInfo", "rustc_compile_action")
 load(":private/utils.bzl", "find_toolchain", "relative_path")
 
-def _find_crate_root_src(srcs, file_names = ["lib.rs"]):
-    """Finds the source file for the crate root."""
-    if len(srcs) == 1:
-        return srcs[0]
-    for src in srcs:
-        if src.basename in file_names:
-            return src
-    fail("No {} source file found.".format(" or ".join(file_names)), "srcs")
-
 def _determine_output_hash(lib_rs):
     return repr(hash(lib_rs.path))
 
@@ -50,8 +41,21 @@ def _determine_lib_name(name, crate_type, toolchain, lib_hash = ""):
         extension = extension,
     )
 
-def _crate_root_src(ctx, file_names = ["lib.rs"]):
-    return ctx.file.crate_root or _find_crate_root_src(ctx.files.srcs, file_names)
+def _crate_root_src(ctx, file_name = "lib.rs"):
+    """Finds the source file for the crate root."""
+    srcs = ctx.files.srcs
+    name_to_file = {f.basename: f for f in srcs}
+
+    crate_root = (
+        ctx.file.crate_root or
+        (srcs[0] if len(srcs) == 1 else None) or
+        name_to_file.get(file_name) or
+        name_to_file.get(ctx.attr.name + ".rs")
+    )
+    if not crate_root:
+        file_names = [file_name, ctx.attr.name + ".rs"]
+        fail("No {} source file found.".format(" or ".join(file_names)), "srcs")
+    return crate_root
 
 def _rust_library_impl(ctx):
     # Find lib.rs
@@ -91,7 +95,7 @@ def _rust_binary_impl(ctx):
         crate_info = CrateInfo(
             name = ctx.label.name,
             type = "bin",
-            root = _crate_root_src(ctx, ["main.rs"]),
+            root = _crate_root_src(ctx, "main.rs"),
             srcs = ctx.files.srcs,
             deps = ctx.attr.deps,
             output = ctx.outputs.executable,