3 files changed, 65 insertions, 34 deletions

diff --git a/tools/go_marshal/defs.bzl b/tools/go_marshal/defs.bzl
index ba98f3599..f44f83eab 100644
--- a/tools/go_marshal/defs.bzl
+++ b/tools/go_marshal/defs.bzl
@@ -4,11 +4,13 @@ def _go_marshal_impl(ctx):
     """Execute the go_marshal tool."""
     output = ctx.outputs.lib
     output_test = ctx.outputs.test
+    output_test_unconditional = ctx.outputs.test_unconditional
 
     # Run the marshal command.
     args = ["-output=%s" % output.path]
-    args += ["-pkg=%s" % ctx.attr.package]
-    args += ["-output_test=%s" % output_test.path]
+    args.append("-pkg=%s" % ctx.attr.package)
+    args.append("-output_test=%s" % output_test.path)
+    args.append("-output_test_unconditional=%s" % output_test_unconditional.path)
 
     if ctx.attr.debug:
         args += ["-debug"]
@@ -18,7 +20,7 @@ def _go_marshal_impl(ctx):
         args += [f.path for f in src.files.to_list()]
     ctx.actions.run(
         inputs = ctx.files.srcs,
-        outputs = [output, output_test],
+        outputs = [output, output_test, output_test_unconditional],
         mnemonic = "GoMarshal",
         progress_message = "go_marshal: %s" % ctx.label,
         arguments = args,
@@ -48,6 +50,7 @@ go_marshal = rule(
     outputs = {
         "lib": "%{name}_unsafe.go",
         "test": "%{name}_test.go",
+        "test_unconditional": "%{name}_unconditional_test.go",
     },
 )
 
diff --git a/tools/go_marshal/gomarshal/generator.go b/tools/go_marshal/gomarshal/generator.go
index 72ed6d109..56fbcb5d2 100644
--- a/tools/go_marshal/gomarshal/generator.go
+++ b/tools/go_marshal/gomarshal/generator.go
@@ -68,6 +68,8 @@ type Generator struct {
 	output *os.File
 	// Output file to write generated tests.
 	outputTest *os.File
+	// Output file to write unconditionally generated tests.
+	outputTestUC *os.File
 	// Package name for the generated file.
 	pkg string
 	// Set of extra packages to import in the generated file.
@@ -75,7 +77,7 @@ type Generator struct {
 }
 
 // NewGenerator creates a new code Generator.
-func NewGenerator(srcs []string, out, outTest, pkg string, imports []string) (*Generator, error) {
+func NewGenerator(srcs []string, out, outTest, outTestUnconditional, pkg string, imports []string) (*Generator, error) {
 	f, err := os.OpenFile(out, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
 	if err != nil {
 		return nil, fmt.Errorf("Couldn't open output file %q: %v", out, err)
@@ -84,12 +86,17 @@ func NewGenerator(srcs []string, out, outTest, pkg string, imports []string) (*G
 	if err != nil {
 		return nil, fmt.Errorf("Couldn't open test output file %q: %v", out, err)
 	}
+	fTestUC, err := os.OpenFile(outTestUnconditional, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
+	if err != nil {
+		return nil, fmt.Errorf("Couldn't open unconditional test output file %q: %v", out, err)
+	}
 	g := Generator{
-		inputs:     srcs,
-		output:     f,
-		outputTest: fTest,
-		pkg:        pkg,
-		imports:    newImportTable(),
+		inputs:       srcs,
+		output:       f,
+		outputTest:   fTest,
+		outputTestUC: fTestUC,
+		pkg:          pkg,
+		imports:      newImportTable(),
 	}
 	for _, i := range imports {
 		// All imports on the extra imports list are unconditionally marked as
@@ -454,6 +461,46 @@ func (g *Generator) Run() error {
 // source file.
 func (g *Generator) writeTests(ts []*testGenerator) error {
 	var b sourceBuffer
+
+	// Write the unconditional test file. This file is always compiled,
+	// regardless of what build tags were specified on the original input
+	// files. We use this file to guarantee we never end up with an empty test
+	// file, as that causes the build to fail with "no tests/benchmarks/examples
+	// found".
+	//
+	// There's no easy way to determine ahead of time if we'll end up with an
+	// empty build file since build constraints can arbitrarily cause some of
+	// the original types to be not defined. We also have no way to tell bazel
+	// to omit the entire test suite since the output files are already defined
+	// before go-marshal is called.
+	b.emit("// Automatically generated marshal tests. See tools/go_marshal.\n\n")
+	b.emit("package %s\n\n", g.pkg)
+	b.emit("func Example() {\n")
+	b.inIndent(func() {
+		b.emit("// This example is intentionally empty, and ensures this package contains at\n")
+		b.emit("// least one testable entity. go-marshal is forced to emit a test package if the\n")
+		b.emit("// input package is marked marshallable, but emitting no testable entities \n")
+		b.emit("// results in a build failure.\n")
+	})
+	b.emit("}\n")
+	if err := b.write(g.outputTestUC); err != nil {
+		return err
+	}
+
+	// Now generate the real test file that contains the real types we
+	// processed. These need to be conditionally compiled according to the build
+	// tags, as the original types may not be defined under all build
+	// configurations.
+
+	b.reset()
+	b.emit("// Automatically generated marshal tests. See tools/go_marshal.\n\n")
+
+	// Emit build tags.
+	if t := tags.Aggregate(g.inputs); len(t) > 0 {
+		b.emit(strings.Join(t.Lines(), "\n"))
+		b.emit("\n\n")
+	}
+
 	b.emit("package %s\n\n", g.pkg)
 	if err := b.write(g.outputTest); err != nil {
 		return err
@@ -470,26 +517,6 @@ func (g *Generator) writeTests(ts []*testGenerator) error {
 	}
 
 	// Write test functions.
-
-	// If we didn't generate any Marshallable implementations, we can't just
-	// emit an empty test file, since that causes the build to fail with "no
-	// tests/benchmarks/examples found". Unfortunately we can't signal bazel to
-	// omit the entire package since the outputs are already defined before
-	// go-marshal is called. If we'd otherwise emit an empty test suite, emit an
-	// empty example instead.
-	if len(ts) == 0 {
-		b.reset()
-		b.emit("func Example() {\n")
-		b.inIndent(func() {
-			b.emit("// This example is intentionally empty to ensure this file contains at least\n")
-			b.emit("// one testable entity. go-marshal is forced to emit a test file if a package\n")
-			b.emit("// is marked marshallable, but emitting a test file with no entities results\n")
-			b.emit("// in a build failure.\n")
-		})
-		b.emit("}\n")
-		return b.write(g.outputTest)
-	}
-
 	for _, t := range ts {
 		if err := t.write(g.outputTest); err != nil {
 			return err
diff --git a/tools/go_marshal/main.go b/tools/go_marshal/main.go
index f74be5c29..6e4a3e8c4 100644
--- a/tools/go_marshal/main.go
+++ b/tools/go_marshal/main.go
@@ -31,10 +31,11 @@ import (
 )
 
 var (
-	pkg        = flag.String("pkg", "", "output package")
-	output     = flag.String("output", "", "output file")
-	outputTest = flag.String("output_test", "", "output file for tests")
-	imports    = flag.String("imports", "", "comma-separated list of extra packages to import in generated code")
+	pkg                     = flag.String("pkg", "", "output package")
+	output                  = flag.String("output", "", "output file")
+	outputTest              = flag.String("output_test", "", "output file for tests")
+	outputTestUnconditional = flag.String("output_test_unconditional", "", "output file for unconditional tests")
+	imports                 = flag.String("imports", "", "comma-separated list of extra packages to import in generated code")
 )
 
 func main() {
@@ -61,7 +62,7 @@ func main() {
 		// as an import.
 		extraImports = strings.Split(*imports, ",")
 	}
-	g, err := gomarshal.NewGenerator(flag.Args(), *output, *outputTest, *pkg, extraImports)
+	g, err := gomarshal.NewGenerator(flag.Args(), *output, *outputTest, *outputTestUnconditional, *pkg, extraImports)
 	if err != nil {
 		panic(err)
 	}