Implement a to_weak_pointer utility (#1625)

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

Author: jviotti

src/core/jsonpointer/include/sourcemeta/core/jsonpointer.h

@@ -326,13 +326,33 @@ auto to_pointer(const std::basic_string<JSON::Char, JSON::CharTraits,
 /// const sourcemeta::core::WeakPointer pointer{std::cref(foo)};
 /// const sourcemeta::core::Pointer result{
 ///   sourcemeta::core::to_pointer(pointer)}:
-/// assert(pointer.size() == 1);
-/// assert(pointer.at(0).is_property());
-/// assert(pointer.at(0).to_property() == "foo");
+/// assert(result.size() == 1);
+/// assert(result.at(0).is_property());
+/// assert(result.at(0).to_property() == "foo");
 /// ```
 SOURCEMETA_CORE_JSONPOINTER_EXPORT
 auto to_pointer(const WeakPointer &pointer) -> Pointer;
 
+/// @ingroup jsonpointer
+/// Convert a JSON Pointer into a JSON WeakPointer. For example:
+///
+/// ```cpp
+/// #include <sourcemeta/core/jsonpointer.h>
+/// #include <cassert>
+///
+/// const sourcemeta::core::Pointer pointer{"foo", "bar", "baz"};
+/// const auto result{sourcemeta::core::to_weak_pointer(pointer)};
+/// assert(result.size() == 3);
+/// assert(result.at(0).is_property());
+/// assert(result.at(0).to_property() == "foo");
+/// assert(result.at(1).is_property());
+/// assert(result.at(1).to_property() == "bar");
+/// assert(result.at(2).is_property());
+/// assert(result.at(2).to_property() == "baz");
+/// ```
+SOURCEMETA_CORE_JSONPOINTER_EXPORT
+auto to_weak_pointer(const Pointer &pointer) -> WeakPointer;
+
 /// @ingroup jsonpointer
 ///
 /// Stringify the input JSON Pointer into a given C++ standard output stream.

src/core/jsonpointer/jsonpointer.cc

@@ -270,6 +270,19 @@ auto to_pointer(const WeakPointer &pointer) -> Pointer {
   return result;
 }
 
+auto to_weak_pointer(const Pointer &pointer) -> WeakPointer {
+  WeakPointer result;
+  for (const auto &token : pointer) {
+    if (token.is_property()) {
+      result.push_back(token.to_property());
+    } else {
+      result.push_back(token.to_index());
+    }
+  }
+
+  return result;
+}
+
 auto stringify(const Pointer &pointer,
                std::basic_ostream<JSON::Char, JSON::CharTraits> &stream)
     -> void {

test/jsonpointer/jsonpointer_weakpointer_test.cc

@@ -316,3 +316,18 @@ TEST(JSONWeakPointer_pointer, to_pointer) {
   EXPECT_TRUE(pointer.at(1).is_index());
   EXPECT_EQ(pointer.at(1).to_index(), 0);
 }
+
+TEST(JSONWeakPointer_pointer, to_weak_pointer) {
+  const sourcemeta::core::Pointer pointer{"foo", 1, "baz"};
+  const auto result{sourcemeta::core::to_weak_pointer(pointer)};
+  EXPECT_EQ(result.size(), 3);
+
+  EXPECT_TRUE(result.at(0).is_property());
+  EXPECT_EQ(result.at(0).to_property(), "foo");
+
+  EXPECT_TRUE(result.at(1).is_index());
+  EXPECT_EQ(result.at(1).to_index(), 1);
+
+  EXPECT_TRUE(result.at(2).is_property());
+  EXPECT_EQ(result.at(2).to_property(), "baz");
+}