utils: Add function to check for confined paths

2 files changed, 25 insertions, 0 deletions

diff --git a/src/utils/cpp/path.hpp b/src/utils/cpp/path.hpp
index 3b44748a..bbbbfbf6 100644
--- a/src/utils/cpp/path.hpp
+++ b/src/utils/cpp/path.hpp
@@ -42,4 +42,21 @@
     return *path.lexically_normal().begin() != "..";
 }
 
+/// \brief Perform a confined condition check on a path with respect to
+/// another path. A path is confined wrt another if it is relative and results
+/// in a non-upwards path when applied from the directory of the other path.
+/// This models the situation when a symlink is being resolved inside a tree.
+/// NOTE: No explicit check is done whether applied_to is actually a relative
+/// path, as this is implicit by the non-upwardness condition.
+[[nodiscard]] static auto PathIsConfined(
+    std::filesystem::path const& path,
+    std::filesystem::path const& applied_to) noexcept -> bool {
+    if (path.is_absolute()) {
+        return false;
+    }
+    // check confined upwards condition; this call also handles the case when
+    // applied_to is an absolute path
+    return PathIsNonUpwards(applied_to.parent_path() / path);
+}
+
 #endif
diff --git a/test/utils/cpp/path.test.cpp b/test/utils/cpp/path.test.cpp
index 5a450fd5..7a0ac1fe 100644
--- a/test/utils/cpp/path.test.cpp
+++ b/test/utils/cpp/path.test.cpp
@@ -40,3 +40,11 @@ TEST_CASE("non-upwards condition", "[path]") {
     CHECK_FALSE(PathIsNonUpwards(
         "foo/../bar/../../foo"));  // relative with non-upwards indirection
 }
+
+TEST_CASE("confined upwards condition", "[path]") {
+    CHECK_FALSE(PathIsConfined("/foo", "dummy"));  // absolute path
+    CHECK(PathIsConfined("foo", "dummy"));         // relative non-upwards
+    CHECK(PathIsConfined("../foo", "dummy/bar"));  // upwards, but confined
+    CHECK_FALSE(PathIsConfined("foo/../bar/../../../foo",
+                               "dummy"));  // upwards, not confined
+}