Make the default tracer an optional feature

docs/guides/javascript-api.md

@@ -97,7 +97,7 @@ cache | `false` | makes the generated parser cache results, avoiding exponential
 context | `{}` | contains a map of variables used by `peg.util.vm.runInContext()` when the `output` option is set to `"parser"`
 dependencies | `{}` | parser dependencies, the value is an object which maps variables used to access the dependencies to module IDs used to load them; valid only when `format` is set to `"amd"`, `"commonjs"`, `"es"`, or `"umd"`
 exportVar | `null` | name of an optional global variable into which the generated parser object is assigned to when no module loader is detected; valid only when `format` is set to `"globals"` or `"umd"`
-features | `null` | map of optional features that are set to `true` by default: `"text"`, `"offset"`, `"range"`, `"location"`, `"expected"`, `"error"` and `"filename"`
+features | `null` | map of optional features that are set to `true` by default: `"text"`, `"offset"`, `"range"`, `"location"`, `"expected"`, `"error"`, `"filename"` and `"DefaultTracer"`
 format | `"bare"` | format of the generated parser (`"amd"`, `"bare"`, `"commonjs"`, `"es"`, `"globals"`, or `"umd"`); valid only when `output` is set to `"source"`
 header | `null` | adds additional comments or content after the `Generated by ...` comment; this option is only handled if it's an array or a string:
 optimize | `"speed"` | selects between optimizing the generated parser for parsing speed (`"speed"`) or code size (`"size"`)

lib/compiler/passes/generate-js.js

@@ -1120,6 +1120,8 @@ function generateJS( ast, session, options ) {
 
         if ( options.trace ) {
 
+            if ( use( "DefaultTracer" ) )
+
                 parts.push( [
                     "function peg$DefaultTracer() {",
                     "  this.indentLevel = 0;",
@@ -1177,6 +1179,15 @@ function generateJS( ast, session, options ) {
                     ""
                 ].join( "\n" ) );
 
+            else
+
+                parts.push( [
+                    "var peg$FauxTracer = {",
+                    "  trace: function(event) { }",
+                    "};",
+                    ""
+                ].join( "\n" ) );
+
         }
 
         parts.push( [
@@ -1257,11 +1268,20 @@ function generateJS( ast, session, options ) {
 
             }
 
+            if ( use( "DefaultTracer" ) )
+
                 parts.push( [
                     "  var peg$tracer = \"tracer\" in options ? options.tracer : new peg$DefaultTracer();",
                     ""
                 ].join( "\n" ) );
 
+            else
+
+                parts.push( [
+                    "  var peg$tracer = \"tracer\" in options ? options.tracer : peg$FauxTracer;",
+                    ""
+                ].join( "\n" ) );
+
         }
 
         parts.push( [
@@ -1595,7 +1615,7 @@ function generateJS( ast, session, options ) {
 
         function generateParserObject() {
 
-            return options.trace
+            return options.trace && use( "DefaultTracer" )
                 ? [
                     "{",
                     "  SyntaxError: peg$SyntaxError,",
@@ -1614,7 +1634,7 @@ function generateJS( ast, session, options ) {
 
         function generateParserExports() {
 
-            return options.trace
+            return options.trace && use( "DefaultTracer" )
                 ? [
                     "{",
                     "  peg$SyntaxError as SyntaxError,",

lib/typings/api.d.ts

@@ -408,6 +408,7 @@ declare namespace peg {
             expected: boolean;
             error: boolean;
             filename: boolean;
+            DefaultTracer: boolean;
 
         }