Bazel now can build dynamic library from cc_library

Working towards: https://github.com/bazelbuild/bazel/issues/3311

When building dynamic library on Windows, Bazel builds an import library
and a DLL.

Bazel provides a feature called windows_export_all_symbols, if this
feature is enabled(and no_windows_export_all_symbols is not) for a
cc_library, then Bazel parses object files of that cc_library to generate
a DEF file that will be used during linking time to export symbols from
DLL. This feature can be specified at crosstool, package, target and
command line level.

A few differences from Unix platforms:

1. We don't build the shared library on Windows by default, users have to
specifiy --output_groups=dynamic_library for building dynamic libraries.
This output group is also available on other platforms.

2. By default, cc_test is dynamically linked on Unix, but it will be
statically linked on Windows by default. (meaning the default value of
linkstatic in cc_test is 1 on Windows, and 0 on other platforms)

3. For global data symbols, __declspec(dllimport) must still be used in
source files.

Remaining issues:

1. Extensions for import library and DLL are not correct yet.
2. DLLs are not guaranteed to be available during runtime yet.
3. Diamond problem
If a cc_library A is specified as linkstatic=0, then no dynamic library
will be built for it, so if another cc_library B depends on it, A will
be statically linked into B, and if a cc_binary C depends on B, A will
also be statically linked into C and B will be dynamically linked to C.
This is wrong because A is duplicated in both B and C.
It is essentially a diamond problem describled in C++ Transitive Library.
(https://docs.google.com/document/d/1-tv0_79zGyBoDmaP_pYWaBVUwHUteLpAs90_rUl-VY8/edit?usp=sharing)
Hopefully, we can avoid this by using cc_shared_library rule in future.

Change-Id: I23640d4caf8afe65d60b1522af6368536d7a8408
PiperOrigin-RevId: 168829958

1 files changed, 24 insertions, 9 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcLibrary.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcLibrary.java
index b846dfaef3..e90dda7c54 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcLibrary.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcLibrary.java
@@ -187,11 +187,17 @@ public abstract class CcLibrary implements RuleConfiguredTargetFactory {
     // doesn't support it, then register an action which complains when triggered,
     // which only happens when some rule explicitly depends on the dynamic library.
     if (!createDynamicLibrary && !supportsDynamicLinker) {
-      Artifact solibArtifact =
+      ImmutableList.Builder<Artifact> dynamicLibraries = ImmutableList.builder();
+      dynamicLibraries.add(
+        CppHelper.getLinuxLinkedArtifact(
+          ruleContext, ruleContext.getConfiguration(), LinkTargetType.DYNAMIC_LIBRARY));
+      if (ccToolchain.getCppConfiguration().useInterfaceSharedObjects()) {
+        dynamicLibraries.add(
           CppHelper.getLinuxLinkedArtifact(
-              ruleContext, ruleContext.getConfiguration(), LinkTargetType.DYNAMIC_LIBRARY);
+            ruleContext, ruleContext.getConfiguration(), LinkTargetType.INTERFACE_DYNAMIC_LIBRARY));
+      }
       ruleContext.registerAction(new FailAction(ruleContext.getActionOwner(),
-          ImmutableList.of(solibArtifact), "Toolchain does not support dynamic linking"));
+          dynamicLibraries.build(), "Toolchain does not support dynamic linking"));
     } else if (!createDynamicLibrary
         && ruleContext.attributes().isConfigurable("srcs")) {
       // If "srcs" is configurable, the .so output is always declared because the logic that
@@ -199,11 +205,17 @@ public abstract class CcLibrary implements RuleConfiguredTargetFactory {
       // Here, where we *do* have the correct value, it may not contain any source files to
       // generate an .so with. If that's the case, register a fake generating action to prevent
       // a "no generating action for this artifact" error.
-      Artifact solibArtifact =
+      ImmutableList.Builder<Artifact> dynamicLibraries = ImmutableList.builder();
+      dynamicLibraries.add(
+        CppHelper.getLinuxLinkedArtifact(
+          ruleContext, ruleContext.getConfiguration(), LinkTargetType.DYNAMIC_LIBRARY));
+      if (ccToolchain.getCppConfiguration().useInterfaceSharedObjects()) {
+        dynamicLibraries.add(
           CppHelper.getLinuxLinkedArtifact(
-              ruleContext, ruleContext.getConfiguration(), LinkTargetType.DYNAMIC_LIBRARY);
+            ruleContext, ruleContext.getConfiguration(), LinkTargetType.INTERFACE_DYNAMIC_LIBRARY));
+      }
       ruleContext.registerAction(new FailAction(ruleContext.getActionOwner(),
-          ImmutableList.of(solibArtifact), "configurable \"srcs\" triggers an implicit .so output "
+          dynamicLibraries.build(), "configurable \"srcs\" triggers an implicit .so output "
           + "even though there are no sources to compile in this configuration"));
     }
 
@@ -258,9 +270,12 @@ public abstract class CcLibrary implements RuleConfiguredTargetFactory {
     NestedSetBuilder<Artifact> filesBuilder = NestedSetBuilder.stableOrder();
     filesBuilder.addAll(LinkerInputs.toLibraryArtifacts(linkedLibraries.getStaticLibraries()));
     filesBuilder.addAll(LinkerInputs.toLibraryArtifacts(linkedLibraries.getPicStaticLibraries()));
-    filesBuilder.addAll(LinkerInputs.toNonSolibArtifacts(linkedLibraries.getDynamicLibraries()));
-    filesBuilder.addAll(
-        LinkerInputs.toNonSolibArtifacts(linkedLibraries.getExecutionDynamicLibraries()));
+
+    if (!featureConfiguration.isEnabled(CppRuleClasses.TARGETS_WINDOWS)) {
+      filesBuilder.addAll(LinkerInputs.toNonSolibArtifacts(linkedLibraries.getDynamicLibraries()));
+      filesBuilder.addAll(
+          LinkerInputs.toNonSolibArtifacts(linkedLibraries.getExecutionDynamicLibraries()));
+    }
 
     CcLinkingOutputs linkingOutputs = info.getCcLinkingOutputs();
     if (!featureConfiguration.isEnabled(CppRuleClasses.HEADER_MODULE_CODEGEN)) {