From 829e1e9378e710c26ea0860cca6c651da6964095 Mon Sep 17 00:00:00 2001
From: Ivan Lozano <ivanlozano@google.com>
Date: Mon, 9 Oct 2023 11:30:09 -0400
Subject: [PATCH] rust: Emit -x c++ for bindgen modules with cpp_std

rust_bindgen modules which defined cpp_std with a .h file were not
correctly emitting the `-x c++` flag. This CL addresses that, and
ensures that if either cpp_std or c_std is set then the appropriate
behavior occurs no matter the file extension.

Bug: 304269101
Test: Soong tests
Change-Id: I71a8ae30ac0ed502d9d3fbf2f3039b0c56529d39
---
 rust/bindgen.go      |  8 +++++---
 rust/bindgen_test.go | 12 +++++++++++-
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/rust/bindgen.go b/rust/bindgen.go
index a80a587f1..ffe532fcb 100644
--- a/rust/bindgen.go
+++ b/rust/bindgen.go
@@ -124,18 +124,20 @@ func (b *bindgenDecorator) getStdVersion(ctx ModuleContext, src android.Path) (s
 		ctx.PropertyErrorf("c_std", "c_std and cpp_std cannot both be defined at the same time.")
 	}
 
-	if String(b.ClangProperties.Cpp_std) != "" {
+	if b.ClangProperties.Cpp_std != nil {
+		isCpp = true
 		if String(b.ClangProperties.Cpp_std) == "experimental" {
 			stdVersion = cc_config.ExperimentalCppStdVersion
-		} else if String(b.ClangProperties.Cpp_std) == "default" {
+		} else if String(b.ClangProperties.Cpp_std) == "default" || String(b.ClangProperties.Cpp_std) == "" {
 			stdVersion = cc_config.CppStdVersion
 		} else {
 			stdVersion = String(b.ClangProperties.Cpp_std)
 		}
 	} else if b.ClangProperties.C_std != nil {
+		isCpp = false
 		if String(b.ClangProperties.C_std) == "experimental" {
 			stdVersion = cc_config.ExperimentalCStdVersion
-		} else if String(b.ClangProperties.C_std) == "default" {
+		} else if String(b.ClangProperties.C_std) == "default" || String(b.ClangProperties.C_std) == "" {
 			stdVersion = cc_config.CStdVersion
 		} else {
 			stdVersion = String(b.ClangProperties.C_std)
diff --git a/rust/bindgen_test.go b/rust/bindgen_test.go
index 12cdb3cb4..0ba0ff840 100644
--- a/rust/bindgen_test.go
+++ b/rust/bindgen_test.go
@@ -115,7 +115,7 @@ func TestRustBindgenStdVersions(t *testing.T) {
 	ctx := testRust(t, `
 		rust_bindgen {
 			name: "libbindgen_cstd",
-			wrapper_src: "src/any.h",
+			wrapper_src: "src/any.hpp",
 			crate_name: "bindgen",
 			stem: "libbindgen",
 			source_stem: "bindings",
@@ -141,6 +141,16 @@ func TestRustBindgenStdVersions(t *testing.T) {
 	if !strings.Contains(libbindgen_cppstd.Args["cflags"], "-std=foo") {
 		t.Errorf("cpp_std value not passed in to rust_bindgen as a clang flag")
 	}
+
+	// Make sure specifying cpp_std emits the '-x c++' flag
+	if !strings.Contains(libbindgen_cppstd.Args["cflags"], "-x c++") {
+		t.Errorf("Setting cpp_std should cause the '-x c++' flag to be emitted")
+	}
+
+	// Make sure specifying c_std omits the '-x c++' flag
+	if strings.Contains(libbindgen_cstd.Args["cflags"], "-x c++") {
+		t.Errorf("Setting c_std should not cause the '-x c++' flag to be emitted")
+	}
 }
 
 func TestBindgenDisallowedFlags(t *testing.T) {