Fix AST node produced by a single semicolon

Add a script to manually inspect results of parsing a short string.

ref #187

package.json

@@ -51,7 +51,9 @@
     "bench": "vitest bench",
     "doc": "typedoc src/index.ts . --name sonic-weave",
     "preautodoc": "npm run precompile && tsc -p tsconfig-autodoc.json",
-    "autodoc": "node .temp/scripts/builtin-docs.js > BUILTIN.md"
+    "autodoc": "node .temp/scripts/builtin-docs.js > BUILTIN.md",
+    "preinspect-grammar": "npm run compile-sonic-weave-parser",
+    "inspect-grammar": "node scripts/inspect-printable-ascii.js"
   },
   "devDependencies": {
     "@types/node": "20.8.2",

scripts/inspect-printable-ascii.js

@@ -0,0 +1,30 @@
+const {parse} = require('../src/sonic-weave-ast');
+
+console.log(
+  'Iterating over all printable ASCII character to see which are accepted by the parser.'
+);
+
+const ASCII = ['\t', '\n', '\r'];
+
+for (let i = 32; i < 127; ++i) {
+  ASCII.push(String.fromCharCode(i));
+}
+
+for (const source of ASCII) {
+  let result = '*Empty program*';
+  try {
+    const ast = parse(source);
+    if (ast.body.length) {
+      result = ast.body[0].type;
+      if (ast.body.length > 1) {
+        result += '+';
+      }
+      if (result === 'ExpressionStatement') {
+        result += '->' + ast.body[0].expression.type;
+      }
+    }
+  } catch {
+    result = '*Rejects*';
+  }
+  console.log(JSON.stringify(source) + '\t' + result);
+}

src/ast.ts

@@ -69,6 +69,10 @@ export type Identifiers = {
   rest?: Identifier;
 };
 
+export type EmptyStatement = {
+  type: 'EmptyStatement';
+};
+
 export type AssignmentStatement = {
   type: 'AssignmentStatement';
   name: Identifier | Identifiers | ArrayAccess | ArraySlice;
@@ -171,6 +175,7 @@ export type ExpressionStatement = {
 };
 
 export type Statement =
+  | EmptyStatement
   | AssignmentStatement
   | VariableDeclaration
   | ExpressionStatement

src/parser.ts

@@ -295,6 +295,8 @@ export class StatementVisitor {
         return this.visitContinueStatement(node);
       case 'ThrowStatement':
         throw this.visitThrowStatement(node);
+      case 'EmptyStatement':
+        return;
     }
     node satisfies never;
   }

src/sonic-weave.pegjs

@@ -459,8 +459,11 @@ CatchClause
 TryFinalizer = FinallyToken _ @Statement
 
 EmptyStatement
-  = _ ';'
-  / __ SingleLineComment LineTerminatorSequence
+  = (_ ';' / __ SingleLineComment LineTerminatorSequence) {
+    return {
+      type: 'EmptyStatement',
+    };
+  }
 
 ExpressionStatement
   = !("{" / FunctionToken / FunctionAliasToken) expression: (LabeledCommaDecimal / Expression) EOS {