Implement an IO function to check path prefixes (#1934)

Signed-off-by: Juan Cruz Viotti <jv@jviotti.com>

Author: jviotti

src/lang/io/include/sourcemeta/core/io.h

@@ -52,6 +52,21 @@ SOURCEMETA_CORE_IO_EXPORT
 auto weakly_canonical(const std::filesystem::path &path)
     -> std::filesystem::path;
 
+/// @ingroup io
+///
+/// Check if a file path starts with another path. This function assumes the
+/// paths are canonicalised. For example:
+///
+/// ```cpp
+/// #include <sourcemeta/core/io.h>
+/// #include <cassert>
+///
+/// assert(sourcemeta::core::starts_with("/foo/bar", "/foo"));
+/// ```
+SOURCEMETA_CORE_IO_EXPORT
+auto starts_with(const std::filesystem::path &path,
+                 const std::filesystem::path &prefix) -> bool;
+
 /// @ingroup io
 ///
 /// A convenience function to open a stream from a file. For example:

src/lang/io/io.cc

@@ -20,4 +20,21 @@ auto weakly_canonical(const std::filesystem::path &path)
              : std::filesystem::weakly_canonical(path);
 }
 
+auto starts_with(const std::filesystem::path &path,
+                 const std::filesystem::path &prefix) -> bool {
+  auto path_iterator = path.begin();
+  auto prefix_iterator = prefix.begin();
+
+  while (prefix_iterator != prefix.end()) {
+    if (path_iterator == path.end() || *path_iterator != *prefix_iterator) {
+      return false;
+    }
+
+    ++path_iterator;
+    ++prefix_iterator;
+  }
+
+  return true;
+}
+
 } // namespace sourcemeta::core

test/io/CMakeLists.txt

@@ -1,5 +1,9 @@
 sourcemeta_googletest(NAMESPACE sourcemeta PROJECT core NAME io
-  SOURCES io_canonical_test.cc io_weakly_canonical_test.cc io_read_file_test.cc)
+  SOURCES
+    io_canonical_test.cc
+    io_weakly_canonical_test.cc
+    io_starts_with_test.cc
+    io_read_file_test.cc)
 
 target_link_libraries(sourcemeta_core_io_unit
   PRIVATE sourcemeta::core::io)

test/io/io_starts_with_test.cc

@@ -0,0 +1,105 @@
+#include <gtest/gtest.h>
+
+#include <sourcemeta/core/io.h>
+
+#ifdef _WIN32
+
+TEST(IO_starts_with, windows_case_insensitive) {
+  const std::filesystem::path path{"C:\\Foo\\Bar"};
+  const std::filesystem::path prefix{"C:\\foo"};
+  EXPECT_FALSE(sourcemeta::core::starts_with(path, prefix));
+}
+
+TEST(IO_starts_with, windows_different_drive) {
+  const std::filesystem::path path{"D:\\Foo\\Bar"};
+  const std::filesystem::path prefix{"C:\\Foo"};
+  EXPECT_FALSE(sourcemeta::core::starts_with(path, prefix));
+}
+
+TEST(IO_starts_with, windows_drive_letter_no_slash) {
+  const std::filesystem::path path{"C:folder\\sub"};
+  const std::filesystem::path prefix{"C:folder"};
+  EXPECT_TRUE(sourcemeta::core::starts_with(path, prefix));
+}
+
+TEST(IO_starts_with, windows_unc_path) {
+  const std::filesystem::path path{"\\\\server\\share\\folder\\file.txt"};
+  const std::filesystem::path prefix{"\\\\server\\share\\folder"};
+  EXPECT_TRUE(sourcemeta::core::starts_with(path, prefix));
+}
+
+TEST(IO_starts_with, windows_same_chars_not_component) {
+  const std::filesystem::path path{"C:\\foo\\barbaz"};
+  const std::filesystem::path prefix{"C:\\foo\\bar"};
+  EXPECT_FALSE(sourcemeta::core::starts_with(path, prefix));
+}
+
+#else
+
+TEST(IO_starts_with, posix_exact_match) {
+  const std::filesystem::path path{"/foo/bar"};
+  const std::filesystem::path prefix{"/foo/bar"};
+  EXPECT_TRUE(sourcemeta::core::starts_with(path, prefix));
+}
+
+TEST(IO_starts_with, posix_nested_dir) {
+  const std::filesystem::path path{"/foo/bar/baz"};
+  const std::filesystem::path prefix{"/foo/bar"};
+  EXPECT_TRUE(sourcemeta::core::starts_with(path, prefix));
+}
+
+TEST(IO_starts_with, posix_same_chars_not_component) {
+  const std::filesystem::path path{"/foo/barbaz"};
+  const std::filesystem::path prefix{"/foo/bar"};
+  EXPECT_FALSE(sourcemeta::core::starts_with(path, prefix));
+}
+
+TEST(IO_starts_with, posix_trailing_slash) {
+  const std::filesystem::path path{"/foo/bar"};
+  const std::filesystem::path prefix{"/foo/bar/"};
+  EXPECT_FALSE(sourcemeta::core::starts_with(path, prefix));
+}
+
+TEST(IO_starts_with, posix_relative_vs_absolute) {
+  const std::filesystem::path path{"foo/bar"};
+  const std::filesystem::path prefix{"/foo"};
+  EXPECT_FALSE(sourcemeta::core::starts_with(path, prefix));
+}
+
+TEST(IO_starts_with, posix_dot_normalization) {
+  const std::filesystem::path path{"/foo/./bar"};
+  const std::filesystem::path prefix{"/foo/bar"};
+  EXPECT_FALSE(sourcemeta::core::starts_with(path, prefix));
+}
+
+TEST(IO_starts_with, posix_dotdot_normalization) {
+  const std::filesystem::path path{"/foo/baz/../bar"};
+  const std::filesystem::path prefix{"/foo/bar"};
+  EXPECT_FALSE(sourcemeta::core::starts_with(path, prefix));
+}
+
+TEST(IO_starts_with, posix_root_path) {
+  const std::filesystem::path path{"/"};
+  const std::filesystem::path prefix{"/"};
+  EXPECT_TRUE(sourcemeta::core::starts_with(path, prefix));
+}
+
+TEST(IO_starts_with, posix_empty_prefix) {
+  const std::filesystem::path path{"/foo/bar"};
+  const std::filesystem::path prefix{};
+  EXPECT_TRUE(sourcemeta::core::starts_with(path, prefix));
+}
+
+TEST(IO_starts_with, posix_empty_path) {
+  const std::filesystem::path path{};
+  const std::filesystem::path prefix{"/foo"};
+  EXPECT_FALSE(sourcemeta::core::starts_with(path, prefix));
+}
+
+TEST(IO_starts_with, posix_empty_empty) {
+  const std::filesystem::path path{};
+  const std::filesystem::path prefix{};
+  EXPECT_TRUE(sourcemeta::core::starts_with(path, prefix));
+}
+
+#endif