Allow setting supports_start_end_lib crosstool field using feature

This cl allows toolchain owners to express that toolchain supports --start-lib/--end-lib using enabled feature "supports_start_end_lib".

This cl is a step towards #5883. Also
see the rollout doc here:
https://docs.google.com/document/d/1uv4c1zag6KvdI31qdx8C6jiTognXPQrxgsUpVefm9fM/edit#.

Flag removing legacy behavior is #6861

RELNOTES: None.
PiperOrigin-RevId: 226292303

site/docs/crosstool-reference.md

@@ -939,7 +939,7 @@ The following is a reference of `CROSSTOOL` build variables.
 
 
 
-### CROSSTOOL features
+### Well-known features
 
 The following is a reference of `CROSSTOOL` features and their activation
 conditions.
@@ -950,7 +950,7 @@ conditions.
   <tr>
    <td><strong>Feature</strong>
    </td>
-   <td><strong>Activation Condition</strong>
+   <td><strong>Documentation</strong>
    </td>
   </tr>
   <tr>
@@ -993,4 +993,14 @@ conditions.
        requested.
    </td>
   </tr>
+  <tr>
+   <td><strong><code>supports_start_end_lib</code></strong>
+   </td>
+   <td>If enabled (and the option <code>--start_end_lib</code> is set), Bazel
+     will not link against static libraries but instead use the
+     <code>--start-lib/--end-lib</code> linker options to link against objects
+     directly. This speeds up the build since Bazel doesn't have to build
+     static libraries.
+   </td>
+  </tr>
 </table>

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

@@ -577,8 +577,9 @@ public boolean supportsExecOrigin() {
   }
 
   /** Returns whether the toolchain supports the --start-lib/--end-lib options. */
-  public boolean supportsStartEndLib() {
-    return toolchainInfo.supportsStartEndLib();
+  public boolean supportsStartEndLib(FeatureConfiguration featureConfiguration) {
+    return toolchainInfo.supportsStartEndLib()
+        || featureConfiguration.isEnabled(CppRuleClasses.SUPPORTS_START_END_LIB);
   }
 
   /**

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

@@ -810,23 +810,28 @@ public static Artifact createDefFileActions(
    * Returns true if the build implied by the given config and toolchain uses --start-lib/--end-lib
    * ld options.
    */
-  public static boolean useStartEndLib(CppConfiguration config, CcToolchainProvider toolchain) {
-    return config.startEndLibIsRequested() && toolchain.supportsStartEndLib();
+  public static boolean useStartEndLib(
+      CppConfiguration config,
+      CcToolchainProvider toolchain,
+      FeatureConfiguration featureConfiguration) {
+    return config.startEndLibIsRequested() && toolchain.supportsStartEndLib(featureConfiguration);
   }
 
   /**
    * Returns the type of archives being used by the build implied by the given config and toolchain.
    */
   public static Link.ArchiveType getArchiveType(
-      CppConfiguration config, CcToolchainProvider toolchain) {
-    return useStartEndLib(config, toolchain)
+      CppConfiguration config,
+      CcToolchainProvider toolchain,
+      FeatureConfiguration featureConfiguration) {
+    return useStartEndLib(config, toolchain, featureConfiguration)
         ? Link.ArchiveType.START_END_LIB
         : Link.ArchiveType.REGULAR;
   }
 
   /**
    * Returns true if interface shared objects should be used in the build implied by the given
-   * config and toolchain.
+   * cppConfiguration and toolchain.
    */
   public static boolean useInterfaceSharedObjects(
       CppConfiguration config, CcToolchainProvider toolchain) {

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

@@ -382,6 +382,9 @@ public static Label ccToolchainTypeAttribute(RuleDefinitionEnvironment env) {
   /** A string constant for is_cc_fake_binary feature. */
   public static final String IS_CC_FAKE_BINARY = "is_cc_fake_binary";
 
+  /** A feature marking that the toolchain can use --start-lib/--end-lib flags */
+  public static final String SUPPORTS_START_END_LIB = "supports_start_end_lib";
+
   /** Ancestor for all rules that do include scanning. */
   public static final class CcIncludeScanningRule implements RuleDefinition {
     @Override

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

@@ -284,7 +284,8 @@ private void addDynamicInputLinkOptions(
             || input.getArtifactCategory() == ArtifactCategory.INTERFACE_LIBRARY);
     Preconditions.checkState(
         !Link.useStartEndLib(
-            input, CppHelper.getArchiveType(cppConfiguration, ccToolchainProvider)));
+            input,
+            CppHelper.getArchiveType(cppConfiguration, ccToolchainProvider, featureConfiguration)));
     if (featureConfiguration.isEnabled(CppRuleClasses.TARGETS_WINDOWS)
         && ccToolchainProvider.supportsInterfaceSharedObjects()) {
       // On Windows, dynamic library (dll) cannot be linked directly when using toolchains that
@@ -379,7 +380,8 @@ private void addStaticInputLinkOptions(
 
     // start-lib/end-lib library: adds its input object files.
     if (Link.useStartEndLib(
-        input, CppHelper.getArchiveType(cppConfiguration, ccToolchainProvider))) {
+        input,
+        CppHelper.getArchiveType(cppConfiguration, ccToolchainProvider, featureConfiguration))) {
       Iterable<Artifact> archiveMembers = input.getObjectFiles();
       if (!Iterables.isEmpty(archiveMembers)) {
         ImmutableList.Builder<Artifact> nonLtoArchiveMembersBuilder = ImmutableList.builder();
@@ -506,7 +508,8 @@ private Map<Artifact, Artifact> generateLtoMap() {
     // As a bonus, we can rephrase --nostart_end_lib as --features=-start_end_lib and get rid
     // of a command line option.
 
-    Preconditions.checkState(CppHelper.useStartEndLib(cppConfiguration, ccToolchainProvider));
+    Preconditions.checkState(
+        CppHelper.useStartEndLib(cppConfiguration, ccToolchainProvider, featureConfiguration));
     Map<Artifact, Artifact> ltoMap = new HashMap<>();
     for (LtoBackendArtifacts l : allLtoArtifacts) {
       ltoMap.put(l.getBitcodeFile(), l.getObjectFile());

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

@@ -398,7 +398,10 @@ public boolean apply(Artifact artifact) {
           + "}";
 
   public static final String COPY_DYNAMIC_LIBRARIES_TO_BINARY_CONFIGURATION =
-      "" + "feature { " + "  name: 'copy_dynamic_libraries_to_binary'" + "}";
+      "" + "feature { name: 'copy_dynamic_libraries_to_binary' }";
+
+  public static final String SUPPORTS_START_END_LIB_FEATURE =
+      "" + "feature {" + "   name: 'supports_start_end_lib'" + "   enabled: true" + "}";
 
   public static final String TARGETS_WINDOWS_CONFIGURATION =
       ""

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

@@ -39,6 +39,7 @@
 import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.cmdline.PackageIdentifier;
 import com.google.devtools.build.lib.cmdline.RepositoryName;
+import com.google.devtools.build.lib.packages.util.MockCcSupport;
 import com.google.devtools.build.lib.rules.core.CoreRules;
 import com.google.devtools.build.lib.rules.platform.PlatformRules;
 import com.google.devtools.build.lib.rules.repository.CoreWorkspaceRules;
@@ -279,6 +280,26 @@ public void testStartEndLib() throws Exception {
     }
   }
 
+  @Test
+  public void testStartEndLibThroughFeature() throws Exception {
+    AnalysisMock.get()
+        .ccSupport()
+        .setupCrosstool(mockToolsConfig, MockCcSupport.SUPPORTS_START_END_LIB_FEATURE);
+    useConfiguration("--start_end_lib");
+    scratch.file(
+        "test/BUILD",
+        "cc_library(name='lib', srcs=['lib.c'])",
+        "cc_binary(name='bin', srcs=['bin.c'])");
+
+    ConfiguredTarget target = getConfiguredTarget("//test:bin");
+    CppLinkAction action = (CppLinkAction) getGeneratingAction(getExecutable(target));
+    for (Artifact input : action.getInputs()) {
+      String name = input.getFilename();
+      assertThat(!CppFileTypes.ARCHIVE.matches(name) && !CppFileTypes.PIC_ARCHIVE.matches(name))
+          .isTrue();
+    }
+  }
+
   @Test
   public void testTempsWithDifferentExtensions() throws Exception {
     useConfiguration("--cpu=k8", "--save_temps");

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

@@ -25,6 +25,7 @@
 import com.google.devtools.build.lib.analysis.util.AnalysisTestCase;
 import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
 import com.google.devtools.build.lib.cmdline.PackageIdentifier;
+import com.google.devtools.build.lib.rules.cpp.CcToolchainFeatures.FeatureConfiguration;
 import com.google.devtools.build.lib.rules.cpp.CppConfiguration.Tool;
 import com.google.devtools.build.lib.rules.cpp.Link.LinkingMode;
 import com.google.devtools.build.lib.testutil.TestConstants;
@@ -175,7 +176,7 @@ public void testSimpleCompleteConfiguration() throws Exception {
     assertThat(ccProvider.getAbiGlibcVersion()).isEqualTo("abi-libc-version");
 
     assertThat(ccProvider.supportsGoldLinker()).isTrue();
-    assertThat(ccProvider.supportsStartEndLib()).isFalse();
+    assertThat(ccProvider.supportsStartEndLib(FeatureConfiguration.EMPTY)).isFalse();
     assertThat(ccProvider.supportsInterfaceSharedObjects()).isFalse();
     assertThat(ccProvider.supportsEmbeddedRuntimes()).isFalse();
     assertThat(ccProvider.toolchainNeedsPic()).isFalse();
@@ -458,7 +459,7 @@ public void testComprehensiveCompleteConfiguration() throws Exception {
     assertThat(ccProviderA.getToolPathFragment(Tool.STRIP))
         .isEqualTo(getToolPath("path/to/strip-A"));
     assertThat(ccProviderA.supportsGoldLinker()).isTrue();
-    assertThat(ccProviderA.supportsStartEndLib()).isTrue();
+    assertThat(ccProviderA.supportsStartEndLib(FeatureConfiguration.EMPTY)).isTrue();
     assertThat(ccProviderA.supportsEmbeddedRuntimes()).isTrue();
     assertThat(ccProviderA.toolchainNeedsPic()).isTrue();
 
@@ -559,7 +560,7 @@ public void testComprehensiveCompleteConfiguration() throws Exception {
     assertThat(ccProviderC.getAbiGlibcVersion()).isEqualTo("abi-libc-version-C");
     // Don't bother with testing the list of tools again.
     assertThat(ccProviderC.supportsGoldLinker()).isFalse();
-    assertThat(ccProviderC.supportsStartEndLib()).isFalse();
+    assertThat(ccProviderC.supportsStartEndLib(FeatureConfiguration.EMPTY)).isFalse();
     assertThat(ccProviderC.supportsInterfaceSharedObjects()).isFalse();
     assertThat(ccProviderC.supportsEmbeddedRuntimes()).isFalse();
     assertThat(ccProviderC.toolchainNeedsPic()).isFalse();