Use input/output from the config file

docs/guides/command-line.md

@@ -4,6 +4,16 @@ The CLI `pegjs` can be used from terminals to generate a parser from the given g
 
 It's usage signature is: `pegjs [options] [<input_file>] [--]`
 
+### Configuration file
+
+If you provide a configuration file (via `-c` or `--config`) then you can use all the options used by the [PEG.js API](./javascript-api.md), as well as:
+
+* `input` — The grammar used as the input file
+* `output` — Output's generated parser to the provided destination
+
+> 1. Will throw if neither are strings, or the input has already been provided
+> 2. the `output` option for the compiler is not usable from the config
+
 ### Input File
 
 Only one grammar is accepted as the given input file, otherwise the CLI aborts with an error.

gulpfile.js

@@ -59,7 +59,7 @@ task( "benchmark", cb => {
 // Generate the grammar parser.
 task( "build:parser", cb => {
 
-    node( "packages/pegjs/bin/peg src/parser.pegjs -o packages/pegjs/lib/parser.js -c src/pegjs.config.js", cb );
+    node( "packages/pegjs/bin/peg -c src/pegjs.config.js", cb );
 
 } );
 

packages/pegjs/bin/options.js

@@ -58,6 +58,42 @@ function addExtraOptions( config ) {
 
     }
 
+    if ( config.input !== null || config.output !== null ) {
+
+        // We don't want to touch the orignal config, just in case it comes from
+        // a javascript file, in which case its possible the same object is used
+        // for something else, somewhere else.
+        config = util.clone( config );
+        const { input, output } = config;
+
+        if ( input !== null ) {
+
+            if ( typeof input !== "string" )
+
+                abort( "The option `input` must be a string." );
+
+            if ( inputFile !== null )
+
+                abort( `The input file is already set, cannot use: "${ input }".` );
+
+            inputFile = input;
+            delete config.input;
+
+        }
+
+        if ( output !== null ) {
+
+            if ( typeof output !== "string" )
+
+                abort( "The option `output` must be a string." );
+
+            outputFile = output;
+            delete config.output;
+
+        }
+
+    }
+
     options = util.processOptions( config, options );
 
 }

src/pegjs.config.js

@@ -2,6 +2,9 @@
 
 module.exports = {
 
+    input: "src/parser.pegjs",
+    output: "packages/pegjs/lib/parser.js",
+
     header: "/* eslint-disable */",
 
     dependencies: {