[gn build] Make `ninja check-clang` also run Clang's unit tests

[thakis]

Summary

Also add a build file for clang/lib/ASTMatchers/Dynamic, which is only needed by tests (and clang/tools/extra).

Also make llvm/utils/gn/build/sync_source_lists_from_cmake.py check that every CMakeLists.txt file below {lld,clang}/unittests has a corresponding BUILD.gn file, so we notice if new test binaries get added (since the failure mode for missing GN build files for tests is just the tests silently not running in the GN build).

Also add a unittest() macro for defining unit test targets, and add a lengthy comment there about where the unit test binaries go and why.

With this, the build files for //clang are complete.

[thakis]

• add test BUILD.gn support to sync script
• remove bigobj fixme since that issue isn't specific to that file

[thakis]

Add unittest template. This is now ready to go.

[phosek]

llvm/utils/gn/secondary/llvm/utils/unittest/unittest.gni

34

What if someone explicitly sets output_dir in the invoker? We should either preserve that value or assert with an error message that overriding output_dir in unittests is unsupported.

35

You should check if deps is defined and set deps = [] if not, otherwise the attempt to add to non-existent list is going to fail.

[thakis]

comments

[thakis]

Thanks for the fast turnaround!

llvm/utils/gn/secondary/llvm/utils/unittest/unittest.gni

34

Good point, done.

35

I can't imagine that anyone would want a unit test that doesn't at least depend on the code under test. I agree in principle, but I think in practice this would be dead code 100% of the time. Might as well omit it then :-)

[phosek]

LGTM

llvm/utils/gn/build/BUILDCONFIG.gn

 # All targets will get this list of configs by default.
 # Targets can opt out of a config by removing it from their local configs list.
 # If you're adding global flags and don't need targets to be able to opt out,
 # add the flags to compiler_defaults, not to a new config.
-_shared_binary_target_configs = [
+shared_binary_target_configs = [
   "//llvm/utils/gn/build:compiler_defaults",
   "//llvm/utils/gn/build:llvm_code",
   "//llvm/utils/gn/build:warn_covered_switch_default",
 ]
 
 # Apply that default list to the binary target types.
 set_defaults("executable") {
-  configs = _shared_binary_target_configs
+  configs = shared_binary_target_configs
 }
 set_defaults("loadable_module") {
-  configs = _shared_binary_target_configs
+  configs = shared_binary_target_configs
 }
 set_defaults("static_library") {
-  configs = _shared_binary_target_configs
+  configs = shared_binary_target_configs
 }
 set_defaults("shared_library") {
-  configs = _shared_binary_target_configs
+  configs = shared_binary_target_configs
 }
 set_defaults("source_set") {
-  configs = _shared_binary_target_configs
+  configs = shared_binary_target_configs
 }
 
 if (host_os == "win") {
   set_default_toolchain("//llvm/utils/gn/build/toolchain:win")
 } else {
   set_default_toolchain("//llvm/utils/gn/build/toolchain:unix")
 }

llvm/utils/gn/build/sync_source_lists_from_cmake.py

 #!/usr/bin/env python
 
 """Helps to keep BUILD.gn files in sync with the corresponding CMakeLists.txt.
 
 For each BUILD.gn file in the tree, checks if the list of cpp files in
 it is identical to the list of cpp files in the corresponding CMakeLists.txt
-file, and prints the difference if not."""
+file, and prints the difference if not.
+
+Also checks that each CMakeLists.txt file below unittests/ folders that define
+binaries have corresponding BUILD.gn files.
+"""
 
 from __future__ import print_function
 
 import os
 import re
 import subprocess
 
-def main():
+
+def sync_source_lists():
     gn_files = subprocess.check_output(
             ['git', 'ls-files', '*BUILD.gn']).splitlines()
 
     # Matches e.g. |   "foo.cpp",|.
     gn_cpp_re = re.compile(r'^\s*"([^"]+\.(?:cpp|h))",$', re.MULTILINE)
     # Matches e.g. |   "foo.cpp"|.
     cmake_cpp_re = re.compile(r'^\s*([A-Za-z_0-9/-]+\.(?:cpp|h))$',
                               re.MULTILINE)
for gn_file in gn_files:
         add = cmake_cpp - gn_cpp
         if add:
             print('add:\n' + '\n'.join('    "%s",' % a for a in add))
         remove = gn_cpp - cmake_cpp
         if remove:
             print('remove:\n' + '\n'.join(remove))
         print()
 
+
+def sync_unittests():
+    checked = [ 'clang', 'lld' ]
+    for c in checked:
+        for root, _, _ in os.walk(os.path.join(c, 'unittests')):
+            cmake_file = os.path.join(root, 'CMakeLists.txt')
+            if not os.path.exists(cmake_file):
+                continue
+            gn_file = os.path.join('llvm/utils/gn/secondary', root, 'BUILD.gn')
+            if not os.path.exists(gn_file):
+                print('missing GN file %s for unittest CMake file %s' %
+                      (gn_file, cmake_file))
+
+
+def main():
+    sync_source_lists()
+    sync_unittests()
+
+
 if __name__ == '__main__':
     main()

llvm/utils/gn/secondary/clang/lib/ASTMatchers/Dynamic/BUILD.gn

+static_library("Dynamic") {
+  output_name = "clangDynamicASTMatchers"
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/AST",
+    "//clang/lib/ASTMatchers",
+    "//clang/lib/Basic",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "Diagnostics.cpp",
+    "Parser.cpp",
+    "Registry.cpp",
+    "VariantValue.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/test/BUILD.gn

deps = [
     "//clang/tools/clang-diff",
     "//clang/tools/clang-format",
     "//clang/tools/clang-import-test",
     "//clang/tools/clang-offload-bundler",
     "//clang/tools/clang-refactor",
     "//clang/tools/clang-rename",
     "//clang/tools/diagtool",
     "//clang/tools/driver:symlinks",
+    "//clang/unittests",
     "//clang/utils/TableGen:clang-tblgen",
     "//clang/utils/hmaptool",
     "//llvm/tools/llc",
     "//llvm/tools/llvm-bcanalyzer",
     "//llvm/tools/llvm-cat",
     "//llvm/tools/llvm-config",
     "//llvm/tools/llvm-dis",
     "//llvm/tools/llvm-lto",
group("test") {
   }
   if (clang_enable_static_analyzer) {
     deps += [
       "//clang/tools/clang-check",
       "//clang/tools/clang-func-mapping",
     ]
   }
 
-  # FIXME: dep on "//clang/unittests" once it exists
   # FIXME: clang_build_examples
   testonly = true
 }
 
 action("check-clang") {
   script = "$root_out_dir/bin/llvm-lit"
   if (host_os == "win") {
     script += ".py"

llvm/utils/gn/secondary/clang/unittests/AST/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("ASTTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/AST",
+    "//clang/lib/ASTMatchers",
+    "//clang/lib/Analysis",
+    "//clang/lib/Basic",
+    "//clang/lib/Frontend",
+    "//clang/lib/Tooling",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "ASTContextParentMapTest.cpp",
+    "ASTImporterTest.cpp",
+    "ASTTypeTraitsTest.cpp",
+    "ASTVectorTest.cpp",
+    "CommentLexer.cpp",
+    "CommentParser.cpp",
+    "CommentTextTest.cpp",
+    "DataCollectionTest.cpp",
+    "DeclPrinterTest.cpp",
+    "DeclTest.cpp",
+    "EvaluateAsRValueTest.cpp",
+    "ExternalASTSourceTest.cpp",
+    "Language.cpp",
+    "NamedDeclPrinterTest.cpp",
+    "SourceLocationTest.cpp",
+    "StmtPrinterTest.cpp",
+    "StructuralEquivalenceTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/ASTMatchers/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("ASTMatchersTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/AST",
+    "//clang/lib/ASTMatchers",
+    "//clang/lib/Basic",
+    "//clang/lib/Frontend",
+    "//clang/lib/Tooling",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "ASTMatchersInternalTest.cpp",
+    "ASTMatchersNarrowingTest.cpp",
+    "ASTMatchersNodeTest.cpp",
+    "ASTMatchersTraversalTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/ASTMatchers/Dynamic/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("DynamicASTMatchersTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/AST",
+    "//clang/lib/ASTMatchers",
+    "//clang/lib/ASTMatchers/Dynamic",
+    "//clang/lib/Basic",
+    "//clang/lib/Frontend",
+    "//clang/lib/Tooling",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "ParserTest.cpp",
+    "RegistryTest.cpp",
+    "VariantValueTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/Analysis/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("ClangAnalysisTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/AST",
+    "//clang/lib/ASTMatchers",
+    "//clang/lib/Analysis",
+    "//clang/lib/Basic",
+    "//clang/lib/Frontend",
+    "//clang/lib/Tooling",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "CFGTest.cpp",
+    "CloneDetectionTest.cpp",
+    "ExprMutationAnalyzerTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/BUILD.gn

+import("//clang/lib/StaticAnalyzer/Frontend/enable.gni")
+
+group("unittests") {
+  deps = [
+    "AST:ASTTests",
+    "ASTMatchers:ASTMatchersTests",
+    "ASTMatchers/Dynamic:DynamicASTMatchersTests",
+    "Basic:BasicTests",
+    "CodeGen:ClangCodeGenTests",
+    "CrossTU:CrossTUTests",
+    "Driver:ClangDriverTests",
+    "Format:FormatTests",
+    "Index:IndexTests",
+    "Lex:LexTests",
+    "Rename:ClangRenameTests",
+    "Rewrite:RewriteTests",
+    "Sema:SemaTests",
+    "Tooling:ToolingTests",
+  ]
+  if (clang_enable_static_analyzer) {
+    deps += [
+      "Analysis:ClangAnalysisTests",
+      "Frontend:FrontendTests",
+      "StaticAnalyzer:StaticAnalysisTests",
+    ]
+  }
+  if (host_os != "win") {
+    # FIXME: libclang unit tests are disabled on Windows due
+    # to failures, mostly in libclang.VirtualFileOverlay_*.
+    # FIXME: Also, the executable can't find libclang.dll since that's
+    # in a different directory.
+    deps += [ "libclang:libclangTests" ]
+  }
+  testonly = true
+}

llvm/utils/gn/secondary/clang/unittests/Basic/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("BasicTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/Basic",
+    "//clang/lib/Lex",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "CharInfoTest.cpp",
+    "DiagnosticTest.cpp",
+    "FileManagerTest.cpp",
+    "FixedPointTest.cpp",
+    "MemoryBufferCacheTest.cpp",
+    "SourceManagerTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/CodeGen/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("ClangCodeGenTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/AST",
+    "//clang/lib/Basic",
+    "//clang/lib/CodeGen",
+    "//clang/lib/Frontend",
+    "//clang/lib/Lex",
+    "//clang/lib/Parse",
+    "//llvm/lib/IR",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "BufferSourceTest.cpp",
+    "CodeGenExternalTest.cpp",
+    "IncrementalProcessingTest.cpp",
+    "TBAAMetadataTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/CrossTU/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("CrossTUTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/AST",
+    "//clang/lib/Basic",
+    "//clang/lib/CrossTU",
+    "//clang/lib/Frontend",
+    "//clang/lib/Tooling",
+    "//llvm/lib/Support",
+    "//llvm/lib/Target:TargetsToBuild",
+  ]
+  sources = [
+    "CrossTranslationUnitTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/Driver/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("ClangDriverTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/Basic",
+    "//clang/lib/Driver",
+    "//llvm/lib/Option",
+    "//llvm/lib/Support",
+    "//llvm/lib/Target:TargetsToBuild",
+  ]
+  sources = [
+    "DistroTest.cpp",
+    "ModuleCacheTest.cpp",
+    "MultilibTest.cpp",
+    "ToolChainTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/Format/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("FormatTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/Basic",
+    "//clang/lib/Format",
+    "//clang/lib/Frontend",
+    "//clang/lib/Rewrite",
+    "//clang/lib/Tooling/Core",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "CleanupTest.cpp",
+    "FormatTest.cpp",
+    "FormatTestComments.cpp",
+    "FormatTestJS.cpp",
+    "FormatTestJava.cpp",
+    "FormatTestObjC.cpp",
+    "FormatTestProto.cpp",
+    "FormatTestRawStrings.cpp",
+    "FormatTestSelective.cpp",
+    "FormatTestTableGen.cpp",
+    "FormatTestTextProto.cpp",
+    "NamespaceEndCommentsFixerTest.cpp",
+    "SortImportsTestJS.cpp",
+    "SortImportsTestJava.cpp",
+    "SortIncludesTest.cpp",
+    "UsingDeclarationsSorterTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/Frontend/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("FrontendTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/AST",
+    "//clang/lib/Basic",
+    "//clang/lib/CodeGen",
+    "//clang/lib/Frontend",
+    "//clang/lib/FrontendTool",
+    "//clang/lib/Lex",
+    "//clang/lib/Sema",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "ASTUnitTest.cpp",
+    "CodeGenActionTest.cpp",
+    "CompilerInstanceTest.cpp",
+    "FixedPointString.cpp",
+    "FrontendActionTest.cpp",
+    "OutputStreamTest.cpp",
+    "PCHPreambleTest.cpp",
+    "ParsedSourceLocationTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/Index/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("IndexTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/AST",
+    "//clang/lib/Basic",
+    "//clang/lib/Frontend",
+    "//clang/lib/Index",
+    "//clang/lib/Lex",
+    "//clang/lib/Serialization",
+    "//clang/lib/Tooling",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "IndexTests.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/Lex/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("LexTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/AST",
+    "//clang/lib/Basic",
+    "//clang/lib/Lex",
+    "//clang/lib/Parse",
+    "//clang/lib/Sema",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "HeaderMapTest.cpp",
+    "HeaderSearchTest.cpp",
+    "LexerTest.cpp",
+    "PPCallbacksTest.cpp",
+    "PPConditionalDirectiveRecordTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/Rename/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("ClangRenameTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+
+  # We'd like clang/unittests/Tooling/RewriterTestContext.h in the test.
+  include_dirs = [ "../.." ]
+
+  deps = [
+    "//clang/lib/AST",
+    "//clang/lib/ASTMatchers",
+    "//clang/lib/Basic",
+    "//clang/lib/Format",
+    "//clang/lib/Frontend",
+    "//clang/lib/Rewrite",
+    "//clang/lib/Tooling",
+    "//clang/lib/Tooling/Core",
+    "//clang/lib/Tooling/Refactoring",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "RenameAliasTest.cpp",
+    "RenameClassTest.cpp",
+    "RenameEnumTest.cpp",
+    "RenameFunctionTest.cpp",
+    "RenameMemberTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/Rewrite/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("RewriteTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/Rewrite",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "RewriteBufferTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/Sema/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("SemaTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/AST",
+    "//clang/lib/Basic",
+    "//clang/lib/Frontend",
+    "//clang/lib/Parse",
+    "//clang/lib/Sema",
+    "//clang/lib/Tooling",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "CodeCompleteTest.cpp",
+    "ExternalSemaSourceTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/StaticAnalyzer/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("StaticAnalysisTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/lib/Analysis",
+    "//clang/lib/Basic",
+    "//clang/lib/StaticAnalyzer/Core",
+    "//clang/lib/StaticAnalyzer/Frontend",
+    "//clang/lib/Tooling",
+    "//llvm/lib/Support",
+  ]
+  sources = [
+    "AnalyzerOptionsTest.cpp",
+    "RegisterCustomCheckersTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/Tooling/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("ToolingTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  include_dirs = [ "." ]
+  deps = [
+    "//clang/lib/AST",
+    "//clang/lib/ASTMatchers",
+    "//clang/lib/Basic",
+    "//clang/lib/Format",
+    "//clang/lib/Frontend",
+    "//clang/lib/Lex",
+    "//clang/lib/Rewrite",
+    "//clang/lib/Tooling",
+    "//clang/lib/Tooling/Core",
+    "//clang/lib/Tooling/Refactoring",
+    "//llvm/lib/Support",
+    "//llvm/lib/Target:TargetsToBuild",
+  ]
+  sources = [
+    "ASTSelectionTest.cpp",
+    "CastExprTest.cpp",
+    "CommentHandlerTest.cpp",
+    "CompilationDatabaseTest.cpp",
+    "DiagnosticsYamlTest.cpp",
+    "ExecutionTest.cpp",
+    "FixItTest.cpp",
+    "HeaderIncludesTest.cpp",
+    "LexicallyOrderedRecursiveASTVisitorTest.cpp",
+    "LookupTest.cpp",
+    "QualTypeNamesTest.cpp",
+    "RecursiveASTVisitorTestDeclVisitor.cpp",
+    "RecursiveASTVisitorTestPostOrderVisitor.cpp",
+    "RecursiveASTVisitorTestTypeLocVisitor.cpp",
+    "RecursiveASTVisitorTests/Attr.cpp",
+    "RecursiveASTVisitorTests/CXXBoolLiteralExpr.cpp",
+    "RecursiveASTVisitorTests/CXXMemberCall.cpp",
+    "RecursiveASTVisitorTests/CXXOperatorCallExprTraverser.cpp",
+    "RecursiveASTVisitorTests/Class.cpp",
+    "RecursiveASTVisitorTests/ConstructExpr.cpp",
+    "RecursiveASTVisitorTests/DeclRefExpr.cpp",
+    "RecursiveASTVisitorTests/ImplicitCtor.cpp",
+    "RecursiveASTVisitorTests/InitListExprPostOrder.cpp",
+    "RecursiveASTVisitorTests/InitListExprPostOrderNoQueue.cpp",
+    "RecursiveASTVisitorTests/InitListExprPreOrder.cpp",
+    "RecursiveASTVisitorTests/InitListExprPreOrderNoQueue.cpp",
+    "RecursiveASTVisitorTests/IntegerLiteral.cpp",
+    "RecursiveASTVisitorTests/LambdaDefaultCapture.cpp",
+    "RecursiveASTVisitorTests/LambdaExpr.cpp",
+    "RecursiveASTVisitorTests/NestedNameSpecifiers.cpp",
+    "RecursiveASTVisitorTests/ParenExpr.cpp",
+    "RecursiveASTVisitorTests/TemplateArgumentLocTraverser.cpp",
+    "RecursiveASTVisitorTests/TraversalScope.cpp",
+    "RefactoringActionRulesTest.cpp",
+    "RefactoringCallbacksTest.cpp",
+    "RefactoringTest.cpp",
+    "ReplacementsYamlTest.cpp",
+    "RewriterTest.cpp",
+    "ToolingTest.cpp",
+  ]
+}

llvm/utils/gn/secondary/clang/unittests/libclang/BUILD.gn

+import("//llvm/utils/unittest/unittest.gni")
+
+unittest("libclangTests") {
+  configs += [ "//llvm/utils/gn/build:clang_code" ]
+  deps = [
+    "//clang/tools/libclang",
+  ]
+  sources = [
+    "LibclangTest.cpp",
+  ]
+  if (host_os == "mac") {
+    ldflags = [ "-Wl,-rpath," + rebase_path("$root_out_dir/lib") ]
+  }
+}

llvm/utils/gn/secondary/lld/unittests/DriverTests/BUILD.gn

-executable("DriverTests") {
-  # test/Unit/lit.cfg expects unittests in LLD_BINARY_DIR/unittest
-  output_dir = target_out_dir
+import("//llvm/utils/unittest/unittest.gni")
 
+unittest("DriverTests") {
   configs += [ "//llvm/utils/gn/build:lld_code" ]
   deps = [
     "//lld/lib/Driver",
     "//lld/lib/ReaderWriter/MachO",
-    "//llvm/utils/unittest/UnitTestMain",
   ]
   sources = [
     "DarwinLdDriverTest.cpp",
   ]
-  testonly = true
 }

llvm/utils/gn/secondary/lld/unittests/MachOTests/BUILD.gn

-executable("MachOTests") {
-  # test/Unit/lit.cfg expects unittests in LLD_BINARY_DIR/unittest
-  output_dir = target_out_dir
+import("//llvm/utils/unittest/unittest.gni")
 
+unittest("MachOTests") {
   configs += [ "//llvm/utils/gn/build:lld_code" ]
   deps = [
     "//lld/lib/Driver",
     "//lld/lib/ReaderWriter/MachO",
     "//lld/lib/ReaderWriter/YAML",
-    "//llvm/utils/unittest/UnitTestMain",
   ]
   sources = [
     "MachONormalizedFileBinaryReaderTests.cpp",
     "MachONormalizedFileBinaryWriterTests.cpp",
     "MachONormalizedFileToAtomsTests.cpp",
     "MachONormalizedFileYAMLTests.cpp",
   ]
-  testonly = true
 }

llvm/utils/gn/secondary/llvm/utils/unittest/unittest.gni

+# This file defines a template for adding a unittest binary.
+#
+# It's a thin wrapper around GN's built-in executable() target type and
+# accepts the same parameters.
+#
+# Example use:
+#
+#   unittest("FormatTest") {
+#     sources = [ ... ]
+#     ...
+#   }
+
+template("unittest") {
+  executable(target_name) {
+    # Foward everything (configs, sources, deps, ...).
+    forward_variables_from(invoker, "*")
+
+    # Common settings for all unit tests.
+    # Unit test binaries shouldn't go right in out/gn/bin, for two reasons:
+    # 1. That's where production binaries go.
+    # 2. The CMake build doesn't put the unit tests of all projects (clang,
+    #    lld,...) in one directory, so it's not guaranteed that there won't
+    #    be name collisions between test binaries from separate projects.
+    # Each lit suite takes an foo_obj_root parameter and puts temporary files
+    # for lit tests at foo_obj_root/test and looks for unit test binaries
+    # below foo_obj_root/unittests. As long as the BUILD.gn files processing
+    # the lit.site.cfg.py.in files match the output dir here, it doesn't
+    # matter all that much where the unit test binaries go, with the weak
+    # constraints that test binaries of different projects should go in
+    # different folders, and that it's not too difficult to manually
+    # run the unit test binary if necessary. Using target_out_dir here
+    # means that //clang/unittests/Format gets its binary in
+    # out/gn/obj/clang/unittests/Format/FormatTests, which seems fine.
+    output_dir = target_out_dir
+    deps += [
+      "//llvm/utils/unittest/UnitTestMain",
+    ]
+    testonly = true
+  }
+}
+
+set_defaults("unittest") {
+  configs = shared_binary_target_configs
+}