Add tests showing usage of String.

cc_bindings_from_rs/test/string/BUILD

@@ -0,0 +1,34 @@
+"""End-to-end tests of `cc_bindings_from_rs`, focusing on Rust String bindings."""
+
+load(
+    "@rules_rust//rust:defs.bzl",
+    "rust_library",
+)
+load(
+    "//cc_bindings_from_rs/bazel_support:cc_bindings_from_rust_rule.bzl",
+    "cc_bindings_from_rust",
+)
+load("//common:crubit_wrapper_macros_oss.bzl", "crubit_cc_test")
+
+package(default_applicable_licenses = ["//:license"])
+
+rust_library(
+    name = "string",
+    srcs = ["string.rs"],
+)
+
+cc_bindings_from_rust(
+    name = "string_cc_api",
+    crate = ":string",
+)
+
+crubit_cc_test(
+    name = "string_test",
+    srcs = ["string_test.cc"],
+    deps = [
+        ":string_cc_api",
+        "//support/rs_std",
+        "//support/rs_std:rs_alloc",
+        "//testing/base/public:gunit_main",
+    ],
+)

cc_bindings_from_rs/test/string/string.rs

@@ -0,0 +1,23 @@
+// Part of the Crubit project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+//! End-to-end tests of `cc_bindings_from_rs`, focusing on `String` bindings.
+
+pub fn roundtrip_rust_string(val: String) -> String {
+    val
+}
+
+pub fn compute_rust_string_length(val: String) -> usize {
+    val.len()
+}
+
+// The point of this test is to generate bindings for `&String` and not `&str`.
+#[allow(clippy::ptr_arg)]
+pub fn compute_rust_string_ref_length(val: &String) -> usize {
+    val.len()
+}
+
+pub fn append_to_rust_string(val: &mut String, s: &str) {
+    val.push_str(s);
+}

cc_bindings_from_rs/test/string/string_test.cc

@@ -0,0 +1,35 @@
+// Part of the Crubit project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include "cc_bindings_from_rs/test/string/string.h"
+
+#include <utility>
+
+#include "gtest/gtest.h"
+#include "support/rs_std/rs_std.h"
+
+namespace crubit {
+namespace {
+
+TEST(RustStringBridging, Basic) {
+  rs::std::string::String s("hello world");
+  EXPECT_EQ(string::compute_rust_string_length(std::move(s)), 11);
+
+  rs::std::string::String s2("hello world from Rust");
+  rs::std::string::String roundtripped =
+      string::roundtrip_rust_string(std::move(s2));
+  EXPECT_EQ(string::compute_rust_string_length(std::move(roundtripped)), 21);
+}
+
+TEST(RustStringBridging, References) {
+  rs::std::string::String s("hello");
+  EXPECT_EQ(string::compute_rust_string_ref_length(s), 5);
+
+  string::append_to_rust_string(s, " appended");
+  EXPECT_EQ(string::compute_rust_string_ref_length(s), 14);
+  EXPECT_EQ(s.as_str(), "hello appended");
+}
+
+}  // namespace
+}  // namespace crubit