feat: update PLAN.md and add end to end test of the compiler

PLAN.md

@@ -3,7 +3,7 @@
 A Rust-flavored, C-targeting language - built pipeline-first.
 
 **Implementation language:** Rust  
-**Code generation target:** x86-64 (AT&T / Intel syntax `.s` → assembled via GAS or NASM)
+**Code generation target:** Native object files (`.o`) via Cranelift JIT/AOT
 
 ## Phase 1 - Lexer
 
@@ -25,23 +25,25 @@ A Rust-flavored, C-targeting language - built pipeline-first.
 
 ## Phase 3 - Semantic Analysis
 
-- [ ] Implement scope-aware symbol table
-- [ ] Name resolution pass - resolve all `Ident` nodes to their declarations
-- [ ] Type inference / checking for `int` and `bool`
-- [ ] Validate function return types match declared signature
-- [ ] Error on use-before-declaration and undeclared symbols
-- [ ] Unit-test: ill-typed programs produce correct diagnostics
+- [x] Implement scope-aware symbol table (environment)
+- [x] Name resolution pass - resolve all `Ident` nodes to their declarations
+- [x] Hindley-Milner type inference (unification, type variables, occurs check)
+- [x] Integer literal sizing and unary minus type promotion logic
+- [x] Translate untyped AST directly into a fully-typed AST (Typed AST)
+- [x] Validate function return types match declared signature
+- [x] Error on use-before-declaration, undeclared symbols, and type mismatches
+- [x] Unit-test: HM unification, type mappings, and ill-typed program diagnostics
 
-## Phase 4 - x86-64 Code Generation
+## Phase 4 - Code Generation via Cranelift
 
-- [ ] Design a simple intermediate representation (linear IR, or use AST directly)
-- [ ] Implement stack-frame layout for local variables
-- [ ] Emit System V AMD64 ABI-compliant function prologues / epilogues
-- [ ] Codegen for arithmetic & comparison expressions
-- [ ] Codegen for function calls (argument passing via registers)
-- [ ] Codegen for `return` statements
-- [ ] Output `.s` file, assemble with NASM / GAS
-- [ ] End-to-end test: compile a simple `fn` → run → correct exit code
+- [x] Integrate `cranelift-codegen`, `cranelift-frontend`, and `cranelift-object`
+- [x] Implement CLI with `clap` (`--emit-ir` flag, input/output files)
+- [x] Map Typed AST types (`Ty`) to Cranelift IR types
+- [x] Lower functions, parameters, and variable definitions to Cranelift IR
+- [x] Codegen for arithmetic, unary operations, and `return` statements
+- [x] Run built-in optimization passes (constant folding, e-graphs, DCE)
+- [x] Output System V AMD64 ABI-compliant `.o` machine code files
+- [x] End-to-end test: compile a simple `fn` → link via `gcc` → run → correct exit code
 
 ## Planned Features (Backlog)