Print Derived Configuration Report (#517)

feat: print derived config variables
feat: print derived config variables in json
test: 16 new unit tests to support features
test: 1 skipped unit test for discovered bug in yargs with reports param

README.md

@@ -43,6 +43,8 @@ Here is a list of common options. Run `c8 --help` for the full list and document
 | `--per-file` | check thresholds per file | `boolean` | `false` |
 | `--temp-directory` | directory V8 coverage data is written to and read from | `string` | `process.env.NODE_V8_COVERAGE` |
 | `--clean` | should temp files be deleted before script execution | `boolean` | `true` |
+| `--print-config` | prints the derived configuration between defaults and a detected configuration file or a file passed as an argument | `boolean` | `false`
+| `--print-config-format` | format in which to print the derived configuration.  Either text or json. | `string` | `text`
 
 ## Checking for "full" source coverage using `--all`
 

lib/parse-args.js

@@ -7,6 +7,8 @@ const { applyExtends } = require('yargs/helpers')
 const parser = require('yargs-parser')
 const { resolve } = require('path')
 
+const { printConfig } = require('./print-config.js')
+
 function buildYargs (withCommands = false) {
   const yargs = Yargs([])
     .usage('$0 [opts] [script] [opts]')
@@ -158,8 +160,19 @@ function buildYargs (withCommands = false) {
       describe: 'supplying --merge-async will merge all v8 coverage reports asynchronously and incrementally. ' +
         'This is to avoid OOM issues with Node.js runtime.'
     })
+    .options('print-config', {
+      default: false,
+      type: 'boolean',
+      describe: 'Print the derived configuration between command line parameters and loaded configuration file'
+    })
+    // Todo: refactor.  Use parse-args options.
+    .options('print-config-format', {
+      default: 'text',
+      type: 'string',
+      choices: ['text', 'json'],
+      describe: 'Format to print the configuration in.  Accepted formats are either text or json'
+    })
     .pkgConf('c8')
-    .demandCommand(1)
     .check((argv) => {
       if (!argv.tempDirectory) {
         argv.tempDirectory = resolve(argv.reportsDir, 'tmp')
@@ -181,6 +194,10 @@ function buildYargs (withCommands = false) {
   //   }
   // })
 
+  printConfig(yargs, hideInstrumenteeArgs)
+
+  yargs.demandCommand(1)
+
   const checkCoverage = require('./commands/check-coverage')
   const report = require('./commands/report')
   if (withCommands) {