Assume toolchain supportsDynamicLinker from presence of "dynamic_link…

…ing_mode" feature

Toolchains no longer have to provide linking_mode_flags { mode: DYNAMIC } to
state that they support dynamic linking mode. It is enough to provide a feature.

This is part of ongoing work to get rid of linking_mode_flags from the
CROSSTOOL.

RELNOTES: None.
PiperOrigin-RevId: 189890583

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

@@ -320,7 +320,11 @@ public static CppToolchainInfo create(
     this.supportsFission = supportsFission;
     this.supportsStartEndLib = supportsStartEndLib;
     this.supportsEmbeddedRuntimes = supportsEmbeddedRuntimes;
-    this.supportsDynamicLinker = supportsDynamicLinker;
+    this.supportsDynamicLinker =
+        supportsDynamicLinker
+            || toolchainFeatures
+                .getActivatableNames()
+                .contains(CppRuleClasses.DYNAMIC_LINKING_MODE);
     this.supportsInterfaceSharedObjects = supportsInterfaceSharedObjects;
     this.supportsGoldLinker = supportsGoldLinker;
     this.toolchainNeedsPic = toolchainNeedsPic;

src/test/java/com/google/devtools/build/lib/packages/util/BazelMockCcSupport.java

@@ -85,6 +85,7 @@ public void setup(MockToolsConfig config) throws IOException {
         "    toolchains = {",
         "      'local|compiler': ':cc-compiler-local',",
         "      'k8|compiler': ':cc-compiler-k8',",
+        "      'k8|compiler_no_dyn_linker': ':cc-no-dyn-compiler-k8',",
         "      'piii|compiler': ':cc-compiler-piii',",
         "      'darwin|compiler': ':cc-compiler-darwin',",
         "      'ios_x86_64|compiler': ':cc-compiler-ios_x86_64',",
@@ -99,6 +100,13 @@ public void setup(MockToolsConfig config) throws IOException {
         "    module_map = 'crosstool.cppmap', supports_header_parsing = 1,",
         "    objcopy_files = ':empty', static_runtime_libs = [':empty'], strip_files = ':empty',",
         ")",
+        "cc_toolchain(name = 'cc-no-dyn-compiler-k8', all_files = ':empty', ",
+        "    compiler_files = ':empty', cpu = 'k8', compiler = 'compiler_no_dyn_linker', ",
+        "    libc = 'local', dwp_files = ':empty', dynamic_runtime_libs = [':empty'], ",
+        "    ar_files = ':empty', as_files = ':empty', linker_files = ':empty',",
+        "    module_map = 'crosstool.cppmap', supports_header_parsing = 1,",
+        "    objcopy_files = ':empty', static_runtime_libs = [':empty'], strip_files = ':empty',",
+        ")",
         "cc_toolchain(name = 'cc-compiler-ppc', all_files = ':empty', compiler_files = ':empty',",
         "    cpu = 'ppc', compiler = 'compiler', libc = 'local', dwp_files = ':empty',",
         "    dynamic_runtime_libs = [':empty'], ",

src/test/java/com/google/devtools/build/lib/packages/util/MockCcSupport.java

@@ -24,6 +24,7 @@
 import com.google.devtools.build.lib.cmdline.PackageIdentifier;
 import com.google.devtools.build.lib.cmdline.RepositoryName;
 import com.google.devtools.build.lib.rules.cpp.CppCompileAction;
+import com.google.devtools.build.lib.rules.cpp.CppRuleClasses;
 import com.google.devtools.build.lib.rules.cpp.Link.LinkTargetType;
 import com.google.devtools.build.lib.testutil.TestConstants;
 import com.google.devtools.build.lib.vfs.PathFragment;
@@ -128,6 +129,9 @@ public boolean apply(Artifact artifact) {
   /** This feature will prevent bazel from patching the crosstool. */
   public static final String NO_LEGACY_FEATURES_FEATURE = "feature { name: 'no_legacy_features' }";
 
+  public static final String DYNAMIC_LINKING_MODE_FEATURE =
+      "feature { name: '" + CppRuleClasses.DYNAMIC_LINKING_MODE + "'}";
+
   /** Feature expected by the C++ rules when pic build is requested */
   public static final String PIC_FEATURE =
       ""

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

@@ -912,4 +912,23 @@ public void testInlineCtoolchain_withToolchainResolution() throws Exception {
         (CcToolchainProvider) target.get(ToolchainInfo.PROVIDER);
     assertThat(toolchainProvider.getAbi()).isEqualTo("banana");
   }
+
+  @Test
+  public void testSupportsDynamicLinkerCheckFeatures() throws Exception {
+    writeDummyCcToolchain();
+
+    getAnalysisMock()
+        .ccSupport()
+        .setupCrosstool(mockToolsConfig, MockCcSupport.DYNAMIC_LINKING_MODE_FEATURE);
+
+    // To make sure the toolchain doesn't define linking_mode_flags { mode: DYNAMIC } as that would
+    // also result in supportsDynamicLinker returning true
+    useConfiguration("--compiler=compiler_no_dyn_linker", "--cpu=k8");
+
+    ConfiguredTarget target = getConfiguredTarget("//a:b");
+    CcToolchainProvider toolchainProvider =
+        (CcToolchainProvider) target.get(ToolchainInfo.PROVIDER);
+
+    assertThat(toolchainProvider.supportsDynamicLinker()).isTrue();
+  }
 }