cli: generate --help text in JS

Instead of having a custom, static, hand-written string
that is being printed to stdout when `--help` is present,
generate it in JS when requested.

PR-URL: https://github.com/nodejs/node/pull/22490
Reviewed-By: Michaël Zasso <targos@protonmail.com>

2 files changed, 156 insertions, 0 deletions

diff --git a/lib/internal/bootstrap/node.js b/lib/internal/bootstrap/node.js
index 30b177c5a4..069c8bc997 100644
--- a/lib/internal/bootstrap/node.js
+++ b/lib/internal/bootstrap/node.js
@@ -105,6 +105,11 @@
       NativeModule.require('internal/inspector_async_hook').setup();
     }
 
+    if (internalBinding('options').getOptions('--help')) {
+      NativeModule.require('internal/print_help').print(process.stdout);
+      return;
+    }
+
     if (isMainThread) {
       mainThreadSetup.setupChildProcessIpcChannel();
     }
diff --git a/lib/internal/print_help.js b/lib/internal/print_help.js
new file mode 100644
index 0000000000..9d14671973
--- /dev/null
+++ b/lib/internal/print_help.js
@@ -0,0 +1,151 @@
+'use strict';
+const { internalBinding } = require('internal/bootstrap/loaders');
+const { getOptions, types } = internalBinding('options');
+
+const typeLookup = [];
+for (const key of Object.keys(types))
+  typeLookup[types[key]] = key;
+
+// Environment variables are parsed ad-hoc throughout the code base,
+// so we gather the documentation here.
+const { hasIntl, hasSmallICU, hasNodeOptions } = process.binding('config');
+const envVars = new Map([
+  ['NODE_DEBUG', { helpText: "','-separated list of core modules that " +
+    'should print debug information' }],
+  ['NODE_DEBUG_NATIVE', { helpText: "','-separated list of C++ core debug " +
+    'categories that should print debug output' }],
+  ['NODE_DISABLE_COLORS', { helpText: 'set to 1 to disable colors in ' +
+    'the REPL' }],
+  ['NODE_EXTRA_CA_CERTS', { helpText: 'path to additional CA certificates ' +
+    'file' }],
+  ['NODE_NO_WARNINGS', { helpText: 'set to 1 to silence process warnings' }],
+  ['NODE_PATH', { helpText: `'${require('path').delimiter}'-separated list ` +
+    'of directories prefixed to the module search path' }],
+  ['NODE_PENDING_DEPRECATION', { helpText: 'set to 1 to emit pending ' +
+    'deprecation warnings' }],
+  ['NODE_PRESERVE_SYMLINKS', { helpText: 'set to 1 to preserve symbolic ' +
+    'links when resolving and caching modules' }],
+  ['NODE_REDIRECT_WARNINGS', { helpText: 'write warnings to path instead ' +
+    'of stderr' }],
+  ['NODE_REPL_HISTORY', { helpText: 'path to the persistent REPL ' +
+    'history file' }],
+  ['OPENSSL_CONF', { helpText: 'load OpenSSL configuration from file' }]
+].concat(hasIntl ? [
+  ['NODE_ICU_DATA', { helpText: 'data path for ICU (Intl object) data' +
+    hasSmallICU ? '' : ' (will extend linked-in data)' }]
+] : []).concat(hasNodeOptions ? [
+  ['NODE_OPTIONS', { helpText: 'set CLI options in the environment via a ' +
+    'space-separated list' }]
+] : []));
+
+
+function indent(text, depth) {
+  return text.replace(/^/gm, ' '.repeat(depth));
+}
+
+function fold(text, width) {
+  return text.replace(new RegExp(`([^\n]{0,${width}})( |$)`, 'g'),
+                      (_, newLine, end) => newLine + (end === ' ' ? '\n' : ''));
+}
+
+function getArgDescription(type) {
+  switch (typeLookup[type]) {
+    case 'kNoOp':
+    case 'kV8Option':
+    case 'kBoolean':
+      break;
+    case 'kHostPort':
+      return '[host:]port';
+    case 'kInteger':
+    case 'kString':
+    case 'kStringList':
+      return '...';
+    case undefined:
+      break;
+    default:
+      require('assert').fail(`unknown option type ${type}`);
+  }
+}
+
+function format({ options, aliases = new Map(), firstColumn, secondColumn }) {
+  let text = '';
+
+  for (const [
+    name, { helpText, type, value }
+  ] of [...options.entries()].sort()) {
+    if (!helpText) continue;
+
+    let displayName = name;
+    const argDescription = getArgDescription(type);
+    if (argDescription)
+      displayName += `=${argDescription}`;
+
+    for (const [ from, to ] of aliases) {
+      // For cases like e.g. `-e, --eval`.
+      if (to[0] === name && to.length === 1) {
+        displayName = `${from}, ${displayName}`;
+      }
+
+      // For cases like `--inspect-brk[=[host:]port]`.
+      const targetInfo = options.get(to[0]);
+      const targetArgDescription =
+        targetInfo ? getArgDescription(targetInfo.type) : '...';
+      if (from === `${name}=`) {
+        displayName += `[=${targetArgDescription}]`;
+      } else if (from === `${name} <arg>`) {
+        displayName += ` [${targetArgDescription}]`;
+      }
+    }
+
+    let displayHelpText = helpText;
+    if (value === true) {
+      // Mark boolean options we currently have enabled.
+      // In particular, it indicates whether --use-openssl-ca
+      // or --use-bundled-ca is the (current) default.
+      displayHelpText += ' (currently set)';
+    }
+
+    text += displayName;
+    if (displayName.length >= firstColumn)
+      text += '\n' + ' '.repeat(firstColumn);
+    else
+      text += ' '.repeat(firstColumn - displayName.length);
+
+    text += indent(fold(displayHelpText, secondColumn),
+                   firstColumn).trimLeft() + '\n';
+  }
+
+  return text;
+}
+
+function print(stream) {
+  const { options, aliases } = getOptions();
+
+  // TODO(addaleax): Allow a bit of expansion depending on `stream.columns`
+  // if it is set.
+  const firstColumn = 28;
+  const secondColumn = 40;
+
+  options.set('-', { helpText: 'script read from stdin (default; ' +
+                               'interactive mode if a tty)' });
+  options.set('--', { helpText: 'indicate the end of node options' });
+  stream.write(
+    'Usage: node [options] [ -e script | script.js | - ] [arguments]\n' +
+    '       node inspect script.js [arguments]\n\n' +
+    'Options:\n');
+  stream.write(indent(format({
+    options, aliases, firstColumn, secondColumn
+  }), 2));
+
+  stream.write('\nEnvironment variables:\n');
+
+  stream.write(format({
+    options: envVars, firstColumn, secondColumn
+  }));
+
+  stream.write('\nDocumentation can be found at https://nodejs.org/\n');
+}
+
+module.exports = {
+  print
+};