adds support for legacy-peer-deps flag on npm install

lib/cli.js

@@ -25,23 +25,24 @@ const cli = meow({
           Where to check. Defaults to current directory. Use -g for checking global modules.
 
         Options
-          -u, --update          Interactive update.
-          -y, --update-all      Uninteractive update. Apply all updates without prompting.
-          -g, --global          Look at global modules.
-          -s, --skip-unused     Skip check for unused packages.
-          -p, --production      Skip devDependencies.
-          -d, --dev-only        Look at devDependencies only (skip dependencies).
-          -i, --ignore          Ignore dependencies based on succeeding glob.
-          -E, --save-exact      Save exact version (x.y.z) instead of caret (^x.y.z) in package.json.
-          --specials            List of depcheck specials to include in check for unused dependencies.
-          --no-color            Force or disable color output.
-          --no-emoji            Remove emoji support. No emoji in default in CI environments.
-          --debug               Debug output. Throw in a gist when creating issues on github.
+          -u, --update              Interactive update.
+          -y, --update-all          Uninteractive update. Apply all updates without prompting.
+          -g, --global              Look at global modules.
+          -s, --skip-unused         Skip check for unused packages.
+          -p, --production          Skip devDependencies.
+          -d, --dev-only            Look at devDependencies only (skip dependencies).
+          -i, --ignore              Ignore dependencies based on succeeding glob.
+          -E, --save-exact          Save exact version (x.y.z) instead of caret (^x.y.z) in package.json.
+          -l, --legacy-peer-deps    Disable automatic installation of peer dependencies.
+          --specials                List of depcheck specials to include in check for unused dependencies.
+          --no-color                Force or disable color output.
+          --no-emoji                Remove emoji support. No emoji in default in CI environments.
+          --debug                   Debug output. Throw in a gist when creating issues on github.
 
         Examples
-          $ npm-check           # See what can be updated, what isn't being used.
-          $ npm-check ../foo    # Check another path.
-          $ npm-check -gu       # Update globally installed modules by picking which ones to upgrade.
+          $ npm-check               # See what can be updated, what isn't being used.
+          $ npm-check ../foo        # Check another path.
+          $ npm-check -gu           # Update globally installed modules by picking which ones to upgrade.
     `},
     {
         alias: {
@@ -52,7 +53,8 @@ const cli = meow({
             p: 'production',
             d: 'dev-only',
             E: 'save-exact',
-            i: 'ignore'
+            i: 'ignore',
+            l: 'legacy-peer-deps'
         },
         default: {
             dir: pkgDir.sync() || process.cwd(),
@@ -91,7 +93,8 @@ const options = {
     installer: process.env.NPM_CHECK_INSTALLER || 'auto',
     debug: cli.flags.debug,
     spinner: cli.flags.spinner,
-    ignore: cli.flags.ignore
+    ignore: cli.flags.ignore,
+    legacyPeerDeps: cli.flags.legacyPeerDeps
 };
 
 if (options.debug) {

lib/out/install-packages.js

@@ -13,12 +13,14 @@ function install(packages, currentState) {
     const installGlobal = currentState.get('global') ? '--global' : null;
     const saveExact = currentState.get('saveExact') ? '--save-exact' : null;
     const color = chalk.supportsColor ? '--color=always' : null;
+    const legacyPeerDeps = currentState.get("legacyPeerDeps") ? "--legacy-peer-deps" : null;
 
     const npmArgs = ['install']
         .concat(installGlobal)
         .concat(saveExact)
         .concat(packages)
         .concat(color)
+        .concat(legacyPeerDeps)
         .filter(Boolean);
 
     console.log('');

lib/state/state.js

@@ -20,6 +20,7 @@ const defaultOptions = {
     spinner: false,
     installer: 'npm',
     ignore: [],
+    legacyPeerDeps: false,
 
     globalPackages: {},
     cwdPackageJson: {devDependencies: {}, dependencies: {}},