add eslint

.eslintrc.cjs

@@ -0,0 +1,27 @@
+/* eslint-env node */
+module.exports = {
+  ignorePatterns: ["/target/**", "/jest.config.js"],
+  extends: ["eslint:recommended", "plugin:@typescript-eslint/recommended"],
+  parser: "@typescript-eslint/parser",
+  plugins: ["@typescript-eslint"],
+  root: true,
+  rules: {
+    // Sometimes you just need a `while(true)`.
+    "no-constant-condition": "off",
+    // Typescript already checks problematic fallthrough.
+    // The eslint rule is a bit dumb and also complains about
+    // obvious clear fallthrough like `case "a": case "b"`.
+    "no-fallthrough": "off",
+    // Suppress no-unused-vars with leading underscores.
+    "@typescript-eslint/no-unused-vars": [
+      "warn",
+      {
+        varsIgnorePattern: "^_",
+        argsIgnorePattern: "^_",
+      },
+    ],
+    // `any` is genrally bad, but sometimes it's the nicest solution
+    // Just let me use it without any ceremony.
+    "@typescript-eslint/no-explicit-any": "off",
+  },
+};

eslintignore

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

package.json

@@ -13,6 +13,9 @@
   "license": "ISC",
   "devDependencies": {
     "@types/jest": "^29.5.3",
+    "@typescript-eslint/eslint-plugin": "^6.2.0",
+    "@typescript-eslint/parser": "^6.2.0",
+    "eslint": "^8.46.0",
     "jest": "^29.6.1",
     "node-dev": "^8.0.0",
     "prettier": "^2.0.0",

src/lexer.ts

@@ -251,7 +251,7 @@ export function tokenize(input: string): Token[] {
               i++;
             }
             const ident = input.slice(span.start, span.end);
-            let kw = isKeyword(ident);
+            const kw = isKeyword(ident);
             if (kw) {
               tokens.push({ kind: kw, span });
             } else {

src/lower.ts

@@ -331,7 +331,7 @@ function lowerExpr(fcx: FuncContext, instrs: wasm.Instr[], expr: Expr) {
     }
     case "literal": {
       switch (expr.value.kind) {
-        case "str":
+        case "str": {
           const utf8 = encodeUtf8(expr.value.value);
           const idx = appendData(fcx.cx, utf8);
 
@@ -339,6 +339,7 @@ function lowerExpr(fcx: FuncContext, instrs: wasm.Instr[], expr: Expr) {
           instrs.push({ kind: "i32.const", imm: utf8.length });
 
           break;
+        }
         case "int":
           switch (expr.value.type) {
             case "Int":
@@ -573,11 +574,9 @@ function lowerExpr(fcx: FuncContext, instrs: wasm.Instr[], expr: Expr) {
 
       // TODO: Actually do this instead of being naive.
 
-      const isPlace = (expr: Expr) =>
+      const _isPlace = (expr: Expr) =>
         expr.kind === "ident" || expr.kind === "fieldAccess";
 
-      function project() {}
-
       lowerExpr(fcx, instrs, expr.lhs);
 
       switch (expr.lhs.ty!.kind) {

src/parser.ts

@@ -344,6 +344,7 @@ function parseExprCall(t: Token[]): [Token[], Expr] {
 }
 
 function parseExprAtom(startT: Token[]): [Token[], Expr] {
+  // eslint-disable-next-line prefer-const
   let [t, tok] = next(startT);
   const span = tok.span;
 
@@ -354,8 +355,7 @@ function parseExprAtom(startT: Token[]): [Token[], Expr] {
     // This could be a block or a tuple literal. We can only know after
     // parsing the first expression and looking at the delimiter.
 
-    let peek;
+    const [, peek] = next(t);
-    [, peek] = next(t);
     // It's a single element, which we interpret as a block.
     // `(0,)` is the one elem tuple.
     if (peek.kind === ")") {
@@ -579,11 +579,7 @@ function parseCommaSeparatedList<R>(
 
   // () | (a) | (a,) | (a, b)
 
-  while (true) {
+  while (next(t)[1]?.kind !== terminator) {
-    if (next(t)[1]?.kind === terminator) {
-      break;
-    }
-
     let nextValue;
     [t, nextValue] = parser(t);
 

src/resolve.ts

@@ -191,8 +191,8 @@ function resolveModule(
           };
         }
         case "let": {
-          let rhs = this.expr(expr.rhs);
+          const rhs = this.expr(expr.rhs);
-          let type = expr.type && this.type(expr.type);
+          const type = expr.type && this.type(expr.type);
 
           scopes.push(expr.name.name);
           const local = { name: expr.name.name, span: expr.name.span };

src/typeck.test.ts

@@ -1,4 +1,4 @@
-import { TY_INT, TY_STRING, TY_UNIT, Ty } from "./ast";
+import { TY_INT, TY_STRING, TY_UNIT } from "./ast";
 import { DUMMY_SPAN as SPAN } from "./error";
 import { InferContext } from "./typeck";
 

src/typeck.ts

@@ -1,6 +1,5 @@
 import {
   Ast,
-  binaryExprPrecedenceClass,
   BuiltinName,
   COMPARISON_KINDS,
   DEFAULT_FOLDER,
@@ -298,7 +297,7 @@ export function typeck(ast: Ast): Ast {
         }
         case "mod": {
           switch (item.node.modKind.kind) {
-            case "inline":
+            case "inline": {
               const modKind: ModItemKind = {
                 kind: "inline",
                 contents: item.node.modKind.contents.map((item) =>
@@ -313,6 +312,7 @@ export function typeck(ast: Ast): Ast {
                   modKind,
                 },
               };
+            }
             case "extern":
               // Nothing to check.
               return {
@@ -417,7 +417,7 @@ export class InferContext {
    * before calling this.
    */
   private constrainVar(variable: number, ty: Ty) {
-    let root = this.findRoot(variable);
+    const root = this.findRoot(variable);
 
     if (ty.kind === "var") {
       // Now we point our root to the other root to unify the two graphs.
@@ -571,7 +571,9 @@ export function checkBody(
         }
         case "let": {
           const loweredBindingTy = expr.type && lowerAstTy(expr.type);
-          let bindingTy = loweredBindingTy ? loweredBindingTy : infcx.newVar();
+          const bindingTy = loweredBindingTy
+            ? loweredBindingTy
+            : infcx.newVar();
 
           const rhs = this.expr(expr.rhs);
           infcx.assign(bindingTy, rhs.ty!, expr.span);
@@ -772,7 +774,9 @@ export function checkBody(
             }
             default: {
               throw new CompilerError(
-                `cannot access field \`${field.value}\` on type \`${printTy(lhs.ty)}\``,
+                `cannot access field \`${field.value}\` on type \`${printTy(
+                  lhs.ty
+                )}\``,
                 expr.span
               );
             }
@@ -854,7 +858,7 @@ export function checkBody(
 
           const assignedFields = new Set();
 
-          fields.forEach(([name, field], i) => {
+          fields.forEach(([name, field]) => {
             const fieldTy = structTy.fields.find((def) => def[0] === name.name);
             if (!fieldTy) {
               throw new CompilerError(
@@ -928,8 +932,8 @@ export function checkBody(
 }
 
 function checkBinary(expr: Expr & ExprBinary): Expr {
-  let lhsTy = expr.lhs.ty!;
+  const lhsTy = expr.lhs.ty!;
-  let rhsTy = expr.rhs.ty!;
+  const rhsTy = expr.rhs.ty!;
 
   if (COMPARISON_KINDS.includes(expr.binaryKind)) {
     if (lhsTy.kind === "int" && rhsTy.kind === "int") {
@@ -969,7 +973,7 @@ function checkBinary(expr: Expr & ExprBinary): Expr {
 }
 
 function checkUnary(expr: Expr & ExprUnary): Expr {
-  let rhsTy = expr.rhs.ty!;
+  const rhsTy = expr.rhs.ty!;
 
   if (
     expr.unaryKind === "!" &&

src/wasm/wat.ts

@@ -629,12 +629,12 @@ function printStart(start: Start, f: FmtCtx) {
   });
 }
 
-function printElem(_elem: Elem, f: FmtCtx) {
+function printElem(_elem: Elem, _f: FmtCtx) {
   todo();
 }
 
 function printData(data: Data, f: FmtCtx) {
-  let mode = data.mode;
+  const mode = data.mode;
 
   f.sexpr(() => {
     f.keyword("data");