From 6500189d58cb8259906b75b8f77d5c736f3ede75 Mon Sep 17 00:00:00 2001
From: Futago-za Ryuu <futagoza.ryuu@gmail.com>
Date: Wed, 31 Jan 2018 02:17:27 +0000
Subject: [PATCH] Report unused rules (Closes #200)

---
 lib/compiler/index.js                         |  2 +
 lib/compiler/passes/report-unused-rules.js    | 31 +++++++++
 .../passes/report-unused-rules.spec.js        | 64 +++++++++++++++++++
 3 files changed, 97 insertions(+)
 create mode 100644 lib/compiler/passes/report-unused-rules.js
 create mode 100644 test/spec/unit/compiler/passes/report-unused-rules.spec.js

diff --git a/lib/compiler/index.js b/lib/compiler/index.js
index 16bd832..61ea4dc 100644
--- a/lib/compiler/index.js
+++ b/lib/compiler/index.js
@@ -6,6 +6,7 @@ const generateJS = require( "./passes/generate-js" );
 const removeProxyRules = require( "./passes/remove-proxy-rules" );
 const reportDuplicateLabels = require( "./passes/report-duplicate-labels" );
 const reportDuplicateRules = require( "./passes/report-duplicate-rules" );
+const reportUnusedRules = require( "./passes/report-unused-rules" );
 const reportInfiniteRecursion = require( "./passes/report-infinite-recursion" );
 const reportInfiniteRepetition = require( "./passes/report-infinite-repetition" );
 const reportUndefinedRules = require( "./passes/report-undefined-rules" );
@@ -37,6 +38,7 @@ const compiler = {
         check: {
             reportUndefinedRules: reportUndefinedRules,
             reportDuplicateRules: reportDuplicateRules,
+            reportUnusedRules: reportUnusedRules,
             reportDuplicateLabels: reportDuplicateLabels,
             reportInfiniteRecursion: reportInfiniteRecursion,
             reportInfiniteRepetition: reportInfiniteRepetition
diff --git a/lib/compiler/passes/report-unused-rules.js b/lib/compiler/passes/report-unused-rules.js
new file mode 100644
index 0000000..9341c83
--- /dev/null
+++ b/lib/compiler/passes/report-unused-rules.js
@@ -0,0 +1,31 @@
+"use strict";
+
+// Checks that all rules are used.
+function reportUnusedRules( ast, session, options ) {
+
+    const used = {};
+    function yes( node ) {
+
+        used[ node.name || node ] = true;
+
+    }
+
+    options.allowedStartRules.forEach( yes );
+    session.buildVisitor( { rule_ref: yes } )( ast );
+
+    ast.rules.forEach( rule => {
+
+        if ( used[ rule.name ] !== true ) {
+
+            session.warn(
+                `Rule "${ rule.name }" is not referenced.`,
+                rule.location
+            );
+
+        }
+
+    } );
+
+}
+
+module.exports = reportUnusedRules;
diff --git a/test/spec/unit/compiler/passes/report-unused-rules.spec.js b/test/spec/unit/compiler/passes/report-unused-rules.spec.js
new file mode 100644
index 0000000..52b7d9b
--- /dev/null
+++ b/test/spec/unit/compiler/passes/report-unused-rules.spec.js
@@ -0,0 +1,64 @@
+"use strict";
+
+const chai = require( "chai" );
+const helpers = require( "./helpers" );
+const pass = require( "pegjs-dev" ).compiler.passes.check.reportUnusedRules;
+
+chai.use( helpers );
+
+const expect = chai.expect;
+
+describe( "compiler pass |reportUnusedRules|", function () {
+
+    it( "should report rules that are not referenced", function () {
+
+        expect( pass ).to.reportWarning(
+            `
+                start = .
+                unused = .
+            `,
+            `Rule "unused" is not referenced.`
+        );
+
+        expect( pass ).to.reportWarning(
+            `
+                start = .
+                unused = .
+                used = .
+            `,
+            [
+                `Rule "used" is not referenced.`,
+                `Rule "unused" is not referenced.`
+            ]
+        );
+
+    } );
+
+    it( "does not report rules that are referenced", function () {
+
+        expect( pass ).not.to.reportWarning( `start = .` );
+
+        expect( pass ).not.to.reportWarning( `
+            start = used
+            used = .
+        ` );
+
+    } );
+
+    it( "does not report any rules that the generated parser starts parsing from", function () {
+
+        expect( pass ).not.to.reportWarning(
+            `
+                a = "x"
+                b = a
+                c = .+
+            `,
+            null,
+            {
+                allowedStartRules: [ "b", "c" ]
+            }
+        );
+
+    } );
+
+} );