From 30cfa295530a17b53bd1f71202bc8effe976408a Mon Sep 17 00:00:00 2001
From: Futago-za Ryuu <futagoza.ryuu@gmail.com>
Date: Fri, 2 Feb 2018 06:42:03 +0000
Subject: [PATCH] Provide context to parser (#517)

---
 lib/compiler/index.js            |  5 ++++-
 lib/compiler/session.js          |  2 ++
 lib/compiler/vm.js               | 25 +++++++++++++++++++++++++
 test/spec/api/plugin-api.spec.js |  6 +-----
 4 files changed, 32 insertions(+), 6 deletions(-)
 create mode 100644 lib/compiler/vm.js

diff --git a/lib/compiler/index.js b/lib/compiler/index.js
index bf6b5c9..c4569d1 100644
--- a/lib/compiler/index.js
+++ b/lib/compiler/index.js
@@ -13,6 +13,7 @@ const reportUndefinedRules = require( "./passes/report-undefined-rules" );
 const inferenceMatchResult = require( "./passes/inference-match-result" );
 const Session = require( "./session" );
 const util = require( "../util" );
+const vm = require( "./vm" );
 
 function processOptions( options, defaults ) {
 
@@ -28,6 +29,7 @@ function processOptions( options, defaults ) {
 const compiler = {
 
     Session: Session,
+    vm: vm,
 
     // Compiler passes.
     //
@@ -65,6 +67,7 @@ const compiler = {
         options = processOptions( options, {
             allowedStartRules: [ ast.rules[ 0 ].name ],
             cache: false,
+            context: {},
             dependencies: {},
             exportVar: null,
             format: "bare",
@@ -86,7 +89,7 @@ const compiler = {
         switch ( options.output ) {
 
             case "parser":
-                return eval( ast.code );
+                return session.vm.runInContext( ast.code, options.context );
 
             case "source":
                 return ast.code;
diff --git a/lib/compiler/session.js b/lib/compiler/session.js
index 222b355..9bb8bf2 100644
--- a/lib/compiler/session.js
+++ b/lib/compiler/session.js
@@ -6,6 +6,7 @@ const ast = require( "../ast" );
 const GrammarError = require( "../grammar-error" );
 const opcodes = require( "./opcodes" );
 const parser = require( "../parser" );
+const vm = require( "./vm" );
 
 function fatal( message, location ) {
 
@@ -28,6 +29,7 @@ class Session {
         this.parser = options.parser || parser;
         this.passes = options.passes || [];
         this.visitor = options.visitor || ast.visitor;
+        this.vm = options.vm || vm;
 
         if ( typeof options.warn === "function" ) this.warn = options.warn;
         if ( typeof options.error === "function" ) this.error = options.error;
diff --git a/lib/compiler/vm.js b/lib/compiler/vm.js
new file mode 100644
index 0000000..e2b2536
--- /dev/null
+++ b/lib/compiler/vm.js
@@ -0,0 +1,25 @@
+"use strict";
+
+const vm = {
+
+    runInContext( code, context ) {
+
+        const peg$context = typeof context !== "undefined" ? context : {};
+
+        /* eslint indent: 0 */
+        return eval( `
+            ${
+                Object.keys( peg$context )
+                    .map( key => `var ${ key } = peg$context.${ key };` )
+                    .join( "" )
+            }
+            var vm = null, code = null, context = null;
+
+            ${ code }
+        ` );
+
+    },
+
+};
+
+module.exports = vm;
diff --git a/test/spec/api/plugin-api.spec.js b/test/spec/api/plugin-api.spec.js
index fb64885..fdc9427 100644
--- a/test/spec/api/plugin-api.spec.js
+++ b/test/spec/api/plugin-api.spec.js
@@ -102,10 +102,6 @@ describe( "plugin API", function () {
 
                     config.parser = peg.generate( `
 
-                        {
-                            const ast = require( process.cwd() + "/lib/ast" );
-                        }
-
                         start = .* {
                             return new ast.Grammar( void 0, [{
                                 type: "rule",
@@ -118,7 +114,7 @@ describe( "plugin API", function () {
                             }] );
                         }
 
-                    ` );
+                    `, { context: { ast: peg.ast } } );
 
                 }
             };