docs(issues): add the-mod-pathfinder design issue

1 files changed, 61 insertions, 0 deletions

diff --git a/issues/the-mod-pathfinder.md b/issues/the-mod-pathfinder.md
new file mode 100644
index 0000000..5a0a4da
--- /dev/null
+++ b/issues/the-mod-pathfinder.md
@@ -0,0 +1,61 @@
+# The Mod Pathfinder
+
+## Background
+
+Currently, `gen_program!` requires all involved types to be `use`d within their module. Mingling lacks a complete module path analyzer — waiting for `proc-macro-span` to stabilize is clearly not practical, so a solution for obtaining module paths is needed.
+
+## Solution
+
+We plan to create an analyzer called `mingling-mod-pathf`, enabled via Mingling's `"pathf"` feature, to compute the full paths of all defined Mingling types.
+
+### Behavior When Enabled
+
+**`mingling_core`**: If the `builds` feature is enabled, introduces the `mingling::build::analyze_and_build_type_mapping()` method (analysis completed at Build-Time)
+
+**`mingling_macros`**: Modifies the behavior of the `gen_program!()` macro — automatically loads the mapping table from the analysis file generated by `mingling::build::analyze_and_build_type_mapping()`, and directly uses the full `mod::path` instead of `TypeName` (injected at Compile-Time)
+
+## Challenges
+
+`mingling-mod-pathf` needs to understand **all** Mingling syntax features.
+Fortunately, Mingling's type creation is almost always explicit:
+
+```rust
+mod sub {
+    mingling::macros::pack!(ResultMyName = String); // directly creates ..::sub::ResultMyName
+}
+```
+
+There are a few exceptions, such as the implicit Dispatcher provided by `extra_macros`, but these can be inferred from the node name:
+
+```rust
+dispatcher!("remote.add"); // although the type is unknown, we can infer CMDRemoteAdd and EntryRemoteAdd
+```
+
+And also `#[program_setup]`:
+
+```rust
+#[program_setup] // can infer CustomSetup from the function name `custom_setup`
+fn custom_setup(program: &mut Program<ThisProgram>) {
+    program.with_dispatchers((CMD1, CMD2, CMD3, CMD4, CMD5));
+}
+```
+
+## Pathf Output Format
+
+Uses TOML key-value pairs, formatted as follows:
+
+```toml
+ResultRemoteAdd = "crate::mymod::ResultRemoteAdd"
+```
+
+Recommended storage location is under the target directory:
+
+```
+/target/{target}/{crate-name}/type-mapping.toml
+```
+
+## Other Issues
+
+This solution is limited to Mingling's own syntax system. If types like `dispatcher!`, `pack!` are indirectly expanded through macros, the analyzer will not be able to discover them.
+
+However, this approach solves the current main pain points, so this issue can be set aside for now and addressed later.