Add .rlib as an allowed extension for static libraries for C++ rules

With this change we can directly link Rust static libraries into C++ binaries. Without this change we would have to register a symlink action that "renames" the extension from .rlib to .a.

What exactly is rlib?

From https://doc.rust-lang.org/reference/linkage.html:

```
This [rlib] is used as an intermediate artifact and can be thought of as a "static Rust library". These rlib files, unlike staticlib files, are interpreted by the compiler in future linkage. This essentially means that rustc will look for metadata in rlib files like it looks for metadata in dynamic libraries. This form of output is used to produce statically linked executables as well as staticlib outputs.
```

This file is an ar archive, just like regular .a archives. This file can actually be used by linkers directly. Rlib contains an additional metadata file that is ignored by linkers but used by rustc compilations. From the high level, rlib can be thought of as a Clang module + object files in an ar archive.

RELNOTES: None.
PiperOrigin-RevId: 385139708

src/main/java/com/google/devtools/build/lib/rules/cpp/CppFileTypes.java

@@ -162,6 +162,8 @@ public ImmutableList<String> getExtensions() {
           return ImmutableList.of(ext, ".obj");
         }
       };
+  // Static library artifact created by rustc, can be used as a regular archive.
+  public static final FileType RUST_RLIB = FileType.of(".rlib");
 
   // Minimized bitcode file emitted by the ThinLTO compile step and used just for LTO indexing.
   public static final FileType LTO_INDEXING_OBJECT_FILE = FileType.of(".indexing.o");

src/main/java/com/google/devtools/build/lib/rules/cpp/Link.java

@@ -46,15 +46,16 @@ private Link() {} // uninstantiable
   public static final FileTypeSet ONLY_INTERFACE_LIBRARY_FILETYPES =
       FileTypeSet.of(CppFileTypes.INTERFACE_SHARED_LIBRARY);
 
-  public static final FileTypeSet ARCHIVE_LIBRARY_FILETYPES = FileTypeSet.of(
-      CppFileTypes.ARCHIVE,
-      CppFileTypes.PIC_ARCHIVE,
-      CppFileTypes.ALWAYS_LINK_LIBRARY,
-      CppFileTypes.ALWAYS_LINK_PIC_LIBRARY);
-
-  public static final FileTypeSet ARCHIVE_FILETYPES = FileTypeSet.of(
-      CppFileTypes.ARCHIVE,
-      CppFileTypes.PIC_ARCHIVE);
+  public static final FileTypeSet ARCHIVE_LIBRARY_FILETYPES =
+      FileTypeSet.of(
+          CppFileTypes.ARCHIVE,
+          CppFileTypes.PIC_ARCHIVE,
+          CppFileTypes.ALWAYS_LINK_LIBRARY,
+          CppFileTypes.ALWAYS_LINK_PIC_LIBRARY,
+          CppFileTypes.RUST_RLIB);
+
+  public static final FileTypeSet ARCHIVE_FILETYPES =
+      FileTypeSet.of(CppFileTypes.ARCHIVE, CppFileTypes.PIC_ARCHIVE, CppFileTypes.RUST_RLIB);
 
   public static final FileTypeSet LINK_LIBRARY_FILETYPES = FileTypeSet.of(
       CppFileTypes.ALWAYS_LINK_LIBRARY,

src/test/java/com/google/devtools/build/lib/rules/cpp/CppFileTypesTest.java

@@ -33,6 +33,12 @@ public void testTwoDotExtensions() {
     assertThat(CppFileTypes.OBJECT_FILE.matches("test.pic.o")).isFalse();
   }
 
+  @Test
+  public void testRlib() {
+    assertThat(CppFileTypes.RUST_RLIB.matches("foo.a")).isFalse();
+    assertThat(CppFileTypes.RUST_RLIB.matches("foo.rlib")).isTrue();
+  }
+
   @Test
   public void testVersionedSharedLibraries() {
     assertThat(CppFileTypes.SHARED_LIBRARY.matches("somelibrary.so")).isTrue();

src/test/java/com/google/devtools/build/lib/rules/cpp/StarlarkCcCommonTest.java

@@ -1335,8 +1335,8 @@ public void testCcLinkingContextOnWindows() throws Exception {
                     CppRuleClasses.TARGETS_WINDOWS,
                     CppRuleClasses.SUPPORTS_DYNAMIC_LINKER));
     doTestCcLinkingContext(
-        ImmutableList.of("a.a", "libdep2.a", "b.a", "c.a", "d.a", "libdep1.a"),
-        ImmutableList.of("a.pic.a", "b.pic.a", "c.pic.a", "e.pic.a"),
+        ImmutableList.of("a.a", "libdep2.a", "b.rlib", "c.a", "d.a", "libdep1.a"),
+        ImmutableList.of("a.pic.a", "b.rlib", "c.pic.a", "e.pic.a"),
         // The suffix of dynamic library is caculated based on repository name and package path
         // to avoid conflicts with dynamic library from other packages.
         ImmutableList.of("a.so", "libdep2_c092dd9ce2.so", "b.so", "e.so", "libdep1_c092dd9ce2.so"));
@@ -1354,8 +1354,8 @@ public void testCcLinkingContext() throws Exception {
                     CppRuleClasses.SUPPORTS_PIC,
                     CppRuleClasses.SUPPORTS_DYNAMIC_LINKER));
     doTestCcLinkingContext(
-        ImmutableList.of("a.a", "b.a", "c.a", "d.a"),
-        ImmutableList.of("a.pic.a", "libdep2.a", "b.pic.a", "c.pic.a", "e.pic.a", "libdep1.a"),
+        ImmutableList.of("a.a", "b.rlib", "c.a", "d.a"),
+        ImmutableList.of("a.pic.a", "libdep2.a", "b.rlib", "c.pic.a", "e.pic.a", "libdep1.a"),
         ImmutableList.of("a.so", "liba_Slibdep2.so", "b.so", "e.so", "liba_Slibdep1.so"));
   }
 
@@ -1371,8 +1371,8 @@ public void testCcLinkingContextForExperimentalCcSharedLibrary() throws Exceptio
                     CppRuleClasses.SUPPORTS_PIC,
                     CppRuleClasses.SUPPORTS_DYNAMIC_LINKER));
     doTestCcLinkingContext(
-        ImmutableList.of("a.a", "b.a", "c.a", "d.a"),
-        ImmutableList.of("a.pic.a", "libdep2.a", "b.pic.a", "c.pic.a", "e.pic.a", "libdep1.a"),
+        ImmutableList.of("a.a", "b.rlib", "c.a", "d.a"),
+        ImmutableList.of("a.pic.a", "libdep2.a", "b.rlib", "c.pic.a", "e.pic.a", "libdep1.a"),
         ImmutableList.of("a.so", "liba_Slibdep2.so", "b.so", "e.so", "liba_Slibdep1.so"));
   }
 
@@ -1399,13 +1399,13 @@ public void testIncompatibleDepsetForLibrariesToLinkGetter() throws Exception {
                 .filter(x -> x.getStaticLibrary() != null)
                 .map(x -> x.getStaticLibrary().getFilename())
                 .collect(ImmutableList.toImmutableList()))
-        .containsExactly("a.a", "b.a", "c.a", "d.a");
+        .containsExactly("a.a", "b.rlib", "c.a", "d.a");
     assertThat(
             librariesToLink.toList(LibraryToLink.class).stream()
                 .filter(x -> x.getPicStaticLibrary() != null)
                 .map(x -> x.getPicStaticLibrary().getFilename())
                 .collect(ImmutableList.toImmutableList()))
-        .containsExactly("a.pic.a", "libdep2.a", "b.pic.a", "c.pic.a", "e.pic.a", "libdep1.a");
+        .containsExactly("a.pic.a", "libdep2.a", "b.rlib", "c.pic.a", "e.pic.a", "libdep1.a");
     assertThat(
             librariesToLink.toList(LibraryToLink.class).stream()
                 .filter(x -> x.getDynamicLibrary() != null)
@@ -1576,8 +1576,8 @@ private void setUpCcLinkingContextTest(boolean enableExperimentalCcImport) throw
         "   deps = [':c', ':dep2', ':b'],",
         ")",
         "crule(name='b',",
-        "   static_library = 'b.a',",
-        "   pic_static_library = 'b.pic.a',",
+        "   static_library = 'b.rlib',",
+        "   pic_static_library = 'b.rlib',",
         "   dynamic_library = 'b.so',",
         "   deps = [':c', ':d'],",
         "   additional_inputs = ['b.lds'],",
@@ -5223,10 +5223,11 @@ public void testWrongExtensionThrowsError() throws Exception {
     AssertionError e = assertThrows(AssertionError.class, () -> getConfiguredTarget("//foo:bin"));
     assertThat(e)
         .hasMessageThat()
-        .contains("'a.o' does not have any of the allowed extensions .a, .lib or .pic.a");
+        .contains("'a.o' does not have any of the allowed extensions .a, .lib, .pic.a or .rlib");
     assertThat(e)
         .hasMessageThat()
-        .contains("'a.pic.o' does not have any of the allowed extensions .a, .lib or .pic.a");
+        .contains(
+            "'a.pic.o' does not have any of the allowed extensions .a, .lib, .pic.a or .rlib");
     assertThat(e)
         .hasMessageThat()
         .contains("'a.ifso' does not have any of the allowed extensions .so, .dylib or .dll");
@@ -7263,6 +7264,8 @@ public void testExpandedLibraryToLinkApiRaisesError() throws Exception {
     }
   }
 
+
+
   @Test
   public void testExpandedLinkstampApiRaisesError() throws Exception {
     scratch.file(