Stop input and output of cc_library from clobbering each other.

Before this change:
Any given cc_library can only contribute one library with a given name to
targets which depend on it. If an input library has the same name as the
cc_library which it is an input to, the decision of which to use is based
on the link mode. e.g.,

cc_library(
    name = "foo",
    srcs = ["foo.c", "libfoo.so"],
)

will only contribute libfoo.a (a static library containing foo.o) in static mode,
while it will only contribute libfoo.so (the precompiled shared library) in dynamic
mode.

This change alters cc_library's behavior in this case:
* If libfoo.a would be empty (i.e., there are no linkable sources), then
this is allowed. The libfoo.so from srcs is simply passed through. (Previously,
the empty libfoo.a would be forwarded.)
* Otherwise, this is an error.

In the case where there are multiple libraries in the srcs with the same
library identifier (lib[name].[a|so|lo]), cc_library will still choose one
based on the link mode. This behavior has not changed.

Similarly, cc_library will still choose one of its own outputs based on the
link mode. That behavior has not changed either.

RELNOTES[INC]: It is now an error to include a precompiled library (.a, .lo, .so)
in a cc_library which would generate a library with the same name
(e.g., libfoo.so in cc_library foo) if that library also contains other linkable
sources.

--
MOS_MIGRATED_REVID=127569615

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

@@ -15,6 +15,7 @@
 package com.google.devtools.build.lib.rules.cpp;
 
 import com.google.common.base.Function;
+import com.google.common.base.Joiner;
 import com.google.common.base.Predicates;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
@@ -913,14 +914,50 @@ public Info build() {
     CcLinkingOutputs originalLinkingOutputs = ccLinkingOutputs;
     if (!(
         staticLibraries.isEmpty() && picStaticLibraries.isEmpty() && dynamicLibraries.isEmpty())) {
+
+      CcLinkingOutputs.Builder newOutputsBuilder = new CcLinkingOutputs.Builder();
+      if (!ccOutputs.isEmpty()) {
+        // Add the linked outputs of this rule iff we had anything to put in them, but then
+        // make sure we're not colliding with some library added from the inputs.
+        newOutputsBuilder.merge(originalLinkingOutputs);
+        Iterable<LibraryToLink> allLibraries =
+            Iterables.concat(staticLibraries, picStaticLibraries, dynamicLibraries);
+        for (LibraryToLink precompiledLibrary : allLibraries) {
+          List<LibraryToLink> matchingLibs =
+              originalLinkingOutputs.getLibrariesWithSameIdentifierAs(precompiledLibrary);
+          if (!matchingLibs.isEmpty()) {
+            Iterable<String> matchingLibArtifactNames =
+                Iterables.transform(
+                    matchingLibs,
+                    new Function<LibraryToLink, String>() {
+                      @Override
+                      public String apply(LibraryToLink input) {
+                        return input.getOriginalLibraryArtifact().getFilename();
+                      }
+                    });
+            ruleContext.ruleError(
+                "Can't put "
+                    + precompiledLibrary.getArtifact().getFilename()
+                    + " into the srcs of a "
+                    + ruleContext.getRuleClassNameForLogging()
+                    + " with the same name ("
+                    + ruleContext.getRule().getName()
+                    + ") which also contains other code or objects to link; it shares a name with "
+                    + Joiner.on(", ").join(matchingLibArtifactNames)
+                    + " (output compiled and linked from the non-library sources of this rule), "
+                    + "which could cause confusion");
+          }
+        }
+      }
+
       // Merge the pre-compiled libraries (static & dynamic) into the linker outputs.
-      ccLinkingOutputs = new CcLinkingOutputs.Builder()
-          .merge(ccLinkingOutputs)
-          .addStaticLibraries(staticLibraries)
-          .addPicStaticLibraries(picStaticLibraries)
-          .addDynamicLibraries(dynamicLibraries)
-          .addExecutionDynamicLibraries(dynamicLibraries)
-          .build();
+      ccLinkingOutputs =
+          newOutputsBuilder
+              .addStaticLibraries(staticLibraries)
+              .addPicStaticLibraries(picStaticLibraries)
+              .addDynamicLibraries(dynamicLibraries)
+              .addExecutionDynamicLibraries(dynamicLibraries)
+              .build();
     }
 
     DwoArtifactsCollector dwoArtifacts =

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

@@ -68,6 +68,24 @@ public ImmutableList<LibraryToLink> getExecutionDynamicLibraries() {
     return executionDynamicLibraries;
   }
 
+  /**
+   * Returns all libraries in this CcLinkingOutputs with the same library identifier - i.e., those
+   * which would be considered different forms of the same library by getPreferredLibrary.
+   */
+  public List<LibraryToLink> getLibrariesWithSameIdentifierAs(LibraryToLink input) {
+    Iterable<LibraryToLink> allLibraries =
+        Iterables.concat(
+            staticLibraries, picStaticLibraries, dynamicLibraries, executionDynamicLibraries);
+    ImmutableList.Builder<LibraryToLink> result = new ImmutableList.Builder<>();
+    for (LibraryToLink library : allLibraries) {
+      if (libraryIdentifierOf(library.getOriginalLibraryArtifact())
+          .equals(libraryIdentifierOf(input.getOriginalLibraryArtifact()))) {
+        result.add(library);
+      }
+    }
+    return result.build();
+  }
+
   /**
    * Add the ".a", ".pic.a" and/or ".so" files in appropriate order of preference depending on the
    * link preferences.

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

@@ -623,19 +623,8 @@ public void testStaticallyLinkedBinaryNeedsSharedObject() throws Exception {
 
     Iterable<Artifact> libraries = getLinkerInputs(wrapsophos);
 
-    // The "libsavi.a" below is the empty ".a" file created by Blaze for the
-    // "savi" cc_library rule (empty since it has no ".cc" files in "srcs").
-    // The "libsavi.so" below is the "lib/libsavi.so" file from "srcs".
-    //
-    // TODO(blaze-team): (2009) the order here is a bit odd; it would make more sense
-    // to put the library for the rule ("libsavi.a") before the ".so" file
-    // from "srcs" ("libsavi.so").  I think this is because we currently
-    // list all the .so files for a rule before all the .a files for the rule.
     assertThat(baseArtifactNames(libraries))
         .containsAllOf("wrapsophos.pic.o", "libsophosengine.a", "libsavi.so");
-    if (emptyShouldOutputStaticLibrary()) {
-      assertThat(baseArtifactNames(libraries)).contains("libsavi.a");
-    }
   }
 
   @Test

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

@@ -36,6 +36,7 @@
 import com.google.devtools.build.lib.analysis.OutputGroupProvider;
 import com.google.devtools.build.lib.analysis.util.AnalysisMock;
 import com.google.devtools.build.lib.analysis.util.BuildViewTestCase;
+import com.google.devtools.build.lib.packages.ImplicitOutputsFunction;
 import com.google.devtools.build.lib.packages.util.MockCcSupport;
 import com.google.devtools.build.lib.rules.test.InstrumentedFilesProvider;
 import com.google.devtools.build.lib.testutil.TestConstants;
@@ -1009,4 +1010,86 @@ public void testConfigurableSrcs() throws Exception {
     Artifact soOutput = getBinArtifact("libfoo.so", target);
     assertThat(getGeneratingAction(soOutput)).isInstanceOf(FailAction.class);
   }
+
+  @Test
+  public void alwaysAddStaticAndDynamicLibraryToFilesToBuildWhenBuilding() throws Exception {
+    ConfiguredTarget target =
+        scratchConfiguredTarget("a", "b", "cc_library(name = 'b', srcs = ['source.cc'])");
+
+    assertThat(artifactsToStrings(getFilesToBuild(target)))
+        .containsExactly("bin a/libb.a", "bin a/libb.ifso", "bin a/libb.so");
+  }
+
+  @Test
+  public void addOnlyStaticLibraryToFilesToBuildWhenWrappingIffImplicitOutput() throws Exception {
+    // This shared library has the same name as the archive generated by this rule, so it should
+    // override said archive. However, said archive should still be put in files to build.
+    ConfiguredTarget target =
+        scratchConfiguredTarget("a", "b", "cc_library(name = 'b', srcs = ['libb.so'])");
+
+    if (target.getTarget().getAssociatedRule().getRuleClassObject().getImplicitOutputsFunction()
+        != ImplicitOutputsFunction.NONE) {
+      assertThat(artifactsToStrings(getFilesToBuild(target))).containsExactly("bin a/libb.a");
+    } else {
+      assertThat(artifactsToStrings(getFilesToBuild(target))).isEmpty();
+    }
+  }
+
+  @Test
+  public void addStaticLibraryToStaticSharedLinkParamsWhenBuilding() throws Exception {
+    ConfiguredTarget target =
+        scratchConfiguredTarget("a", "foo", "cc_library(name = 'foo', srcs = ['foo.cc'])");
+
+    Iterable<Artifact> libraries =
+        LinkerInputs.toNonSolibArtifacts(
+            target
+                .getProvider(CcLinkParamsProvider.class)
+                .getCcLinkParams(true, true)
+                .getLibraries());
+    assertThat(artifactsToStrings(libraries)).contains("bin a/libfoo.a");
+  }
+
+  @Test
+  public void dontAddStaticLibraryToStaticSharedLinkParamsWhenWrappingSameLibraryIdentifier()
+      throws Exception {
+    ConfiguredTarget target =
+        scratchConfiguredTarget("a", "foo", "cc_library(name = 'foo', srcs = ['libfoo.so'])");
+
+    Iterable<Artifact> libraries =
+        LinkerInputs.toNonSolibArtifacts(
+            target
+                .getProvider(CcLinkParamsProvider.class)
+                .getCcLinkParams(true, true)
+                .getLibraries());
+    assertThat(artifactsToStrings(libraries)).doesNotContain("bin a/libfoo.a");
+    assertThat(artifactsToStrings(libraries)).contains("src a/libfoo.so");
+  }
+
+  @Test
+  public void onlyAddOneWrappedLibraryWithSameLibraryIdentifierToLinkParams() throws Exception {
+    ConfiguredTarget target =
+        scratchConfiguredTarget(
+            "a", "foo", "cc_library(name = 'foo', srcs = ['libfoo.lo', 'libfoo.so'])");
+
+    Iterable<Artifact> libraries =
+        LinkerInputs.toNonSolibArtifacts(
+            target
+                .getProvider(CcLinkParamsProvider.class)
+                .getCcLinkParams(true, true)
+                .getLibraries());
+    assertThat(artifactsToStrings(libraries)).doesNotContain("src a/libfoo.so");
+    assertThat(artifactsToStrings(libraries)).contains("src a/libfoo.lo");
+  }
+
+  @Test
+  public void forbidBuildingAndWrappingSameLibraryIdentifier() throws Exception {
+    checkError(
+        "a",
+        "foo",
+        "in cc_library rule //a:foo: Can't put libfoo.lo into the srcs of a cc_library with the "
+            + "same name (foo) which also contains other code or objects to link; it shares a name "
+            + "with libfoo.a, libfoo.ifso, libfoo.so (output compiled and linked from the "
+            + "non-library sources of this rule), which could cause confusion",
+        "cc_library(name = 'foo', srcs = ['foo.cc', 'libfoo.lo'])");
+  }
 }