Add tools and .gitignore

Mostly going to be changing up how the AST is generated so I want to get
it into git now before I screw too much up.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

.gitignore

@@ -0,0 +1 @@
+/target

tools/genast.py

@@ -0,0 +1,136 @@
+#!/usr/bin/env python3
+import sys
+import time
+from pathlib import Path
+
+GENERATE = [
+    (
+        "Expr",
+        [
+            "Binary     -> lhs: ExprP, op: Token, rhs: ExprP",
+            "Unary      -> op: Token, expr: ExprP",
+            "Call       -> expr: ExprP, args: Vec<ExprP>, rparen: Token",
+            "Get        -> expr: ExprP, name: Token",
+            "Primary    -> token: Token",
+            "Function   -> lparen: Token, params: Vec<(Token <COMMA> Option<ExprP>)>, return_type: Option<ExprP>, body: Vec<StmtP>, rbrace: Token",
+        ],
+    ),
+    (
+        "Stmt",
+        [
+            "Expr       -> expr: ExprP",
+            "Assign     -> lhs: Token, rhs: ExprP",
+            "Set        -> expr: ExprP, name: Token, rhs: ExprP",
+            "Block      -> lbrace: Token, stmts: Vec<StmtP>, rbrace: Token",
+            "Return     -> return_kw: Token, expr: Option<ExprP>",
+            "If         -> if_kw: Token, condition: ExprP, then_branch: BlockStmt, else_branch: Vec<StmtP>",
+        ],
+    ),
+]
+
+
+class FileWriter:
+    def __init__(self, path: Path) -> None:
+        self.path = path
+        self.fp = open(path, "w")
+
+    def write(self, text: str = "") -> None:
+        self.fp.write(text)
+
+    def line(self, line: str = "") -> None:
+        self.fp.write(line)
+        self.fp.write("\n")
+
+
+def define_visitor(wr: FileWriter, base: str, type_lines: list[str]):
+    types = []
+    for line in type_lines:
+        parts = line.split("->")
+        members = [p.strip().replace("<COMMA>", ",") for p in parts[1].split(",")]
+        types += [(parts[0].strip(), members)]
+
+    wr.line(f"pub trait {base}Visitor " + "{")
+
+    for type, members in types:
+        wr.line(
+            f"    fn visit_{type.lower()}_{base.lower()}(&mut self, {base.lower()}: &{type}{base});"
+        )
+    wr.line("}")
+    wr.line()
+
+
+def define_ast(wr: FileWriter, base: str, type_lines: list[str]):
+    types = []
+    for line in type_lines:
+        parts = line.split("->")
+        members = [p.strip().replace("<COMMA>", ",") for p in parts[1].split(",")]
+        types += [(parts[0].strip(), members)]
+
+    visitor = f"{base}Visitor"
+
+    wr.line(f"pub trait {base}: Debug + Any " + "{")
+    wr.line(f"    fn accept(&self, visitor: &mut dyn {visitor});")
+    wr.line("    fn as_any(self: Box<Self>) -> Box<dyn Any>;")
+    wr.line("    fn as_any_ref(&self) -> &dyn Any;")
+    wr.line("}")
+    wr.line()
+    wr.line(f"pub type {base}P = Box<dyn {base} + 'static>;")
+    wr.line()
+
+    for type, members in types:
+        wr.line("#[derive(Debug)]")
+        wr.line(f"pub struct {type}{base} " + "{")
+        for member in members:
+            wr.line(f"    pub {member},")
+        wr.line("}")
+        wr.line()
+        wr.line(f"impl {base} for {type}{base} " + "{")
+        wr.line(f"    fn accept(&self, visitor: &mut dyn {visitor})" + "{")
+        wr.line(f"        visitor.visit_{type.lower()}_{base.lower()}(self);")
+        wr.line("    }")
+        wr.line()
+        wr.line("    fn as_any(self: Box<Self>) -> Box<dyn Any> {")
+        wr.line("        self")
+        wr.line("    }")
+        wr.line()
+        wr.line("    fn as_any_ref(&self) -> &dyn Any {")
+        wr.line("        self")
+        wr.line("    }")
+        wr.line("}")
+        wr.line()
+
+
+def main():
+    if len(sys.argv) == 1:
+        path = Path(__file__).parent / "../src/ast.rs"
+    else:
+        path = Path(sys.argv[1])
+
+    path = path.resolve()
+    print(f"Using {path}")
+
+    wr = FileWriter(path)
+
+    wr.line(
+        "// This is an auto-generated file. Any changes made to this file may be overwritten."
+    )
+    wr.line("// This file was created at: " + time.strftime("%Y-%m-%d %H:%M:%S"))
+
+    # Imports
+    wr.line("use std::fmt::Debug;")
+    wr.line("use std::any::Any;")
+    wr.line()
+    wr.line("use crate::token::Token;")
+    wr.line()
+
+    # Visitors
+    for base, types in GENERATE:
+        define_visitor(wr, base, types)
+
+    # AST
+    for base, types in GENERATE:
+        define_ast(wr, base, types)
+
+
+if __name__ == "__main__":
+    main()