Implement AST transformer

Summary:
Implement an eqWAlizer AST transformer in ELP, based on the AST visitor already implemented.

Add `preprocess` module implementing (for now) the default implementation of the transformer, which is called on every AST/stub going through ELP.

Reviewed By: RobinMorisset

Differential Revision: D60584098

fbshipit-source-id: 52f1a705e2c3616cc08921898276dc345dec9986

crates/eqwalizer/src/ast/mod.rs

@@ -31,6 +31,7 @@ pub mod convert;
 pub mod convert_types;
 pub mod db;
 pub mod expand;
+pub mod preprocess;
 pub mod stub;
 pub mod subst;
 pub mod trans_valid;
@@ -205,7 +206,8 @@ pub fn from_bytes(bytes: &Vec<u8>) -> Result<AST, Error> {
     if let Term::Tuple(res) = term {
         if let [Term::Atom(ok), forms, _] = &res.elements[..] {
             if ok.name == "ok" {
-                return Ok(convert::convert_forms(forms, false, false)?);
+                let converted_forms = convert::convert_forms(forms, false, false)?;
+                return Ok(preprocess::preprocess(converted_forms));
             }
         }
     }

crates/eqwalizer/src/ast/preprocess.rs

@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under both the MIT license found in the
+ * LICENSE-MIT file in the root directory of this source tree and the Apache
+ * License, Version 2.0 found in the LICENSE-APACHE file in the root directory
+ * of this source tree.
+ */
+
+use elp_types_db::eqwalizer::transformer::Transformer;
+use elp_types_db::eqwalizer::AST;
+
+struct Preprocessor {}
+
+impl Transformer<()> for Preprocessor {}
+
+pub(crate) fn preprocess(ast: AST) -> AST {
+    let mut preprocessor = Preprocessor {};
+    preprocessor.transform_ast(ast).unwrap()
+}

crates/types_db/src/eqwalizer/mod.rs

@@ -23,6 +23,7 @@ pub mod guard;
 pub mod invalid_diagnostics;
 pub mod pat;
 pub mod tc_diagnostics;
+pub mod transformer;
 pub mod types;
 pub mod visitor;