feat: suggest installing dependency as devDependency when appropriate (#1052)

app/components/Terminal/Install.vue

···
 <script setup lang="ts">
 import type { JsrPackageInfo } from '#shared/types/jsr'
+import type { DevDependencySuggestion } from '#shared/utils/dev-dependency'
 import type { PackageManagerId } from '~/utils/install-command'
 
 const props = defineProps<{
···
   requestedVersion?: string | null
   installVersionOverride?: string | null
   jsrInfo?: JsrPackageInfo | null
+  devDependencySuggestion?: DevDependencySuggestion | null
   typesPackageName?: string | null
   executableInfo?: { hasExecutable: boolean; primaryCommand?: string } | null
   createPackageInfo?: { packageName: string } | null
···
   })
 }
 
+const devDependencySuggestion = computed(
+  () => props.devDependencySuggestion ?? { recommended: false as const },
+)
+
+function getDevInstallPartsForPM(pmId: PackageManagerId) {
+  return getInstallCommandParts({
+    packageName: props.packageName,
+    packageManager: pmId,
+    version: props.requestedVersion,
+    jsrInfo: props.jsrInfo,
+    dev: true,
+  })
+}
+
 // Generate run command parts for a specific package manager
 function getRunPartsForPM(pmId: PackageManagerId, command?: string) {
   return getRunCommandParts({
···
   const pm = packageManagers.find(p => p.id === pmId)
   if (!pm) return []
 
-  const devFlag = pmId === 'bun' ? '-d' : '-D'
+  const devFlag = getDevDependencyFlag(pmId)
   const pkgSpec = pmId === 'deno' ? `npm:${props.typesPackageName}` : props.typesPackageName
 
   return [pm.label, pm.action, devFlag, pkgSpec]
···
 
 const { copied: createCopied, copy: copyCreate } = useClipboard({ copiedDuring: 2000 })
 const copyCreateCommand = () => copyCreate(getFullCreateCommand())
+
+const { copied: devInstallCopied, copy: copyDevInstall } = useClipboard({ copiedDuring: 2000 })
+const copyDevInstallCommand = () =>
+  copyDevInstall(
+    getInstallCommand({
+      packageName: props.packageName,
+      packageManager: selectedPM.value,
+      version: props.requestedVersion,
+      jsrInfo: props.jsrInfo,
+      dev: true,
+    }),
+  )
 </script>
 
 <template>
···
             <span aria-live="polite">{{ copied ? $t('common.copied') : $t('common.copy') }}</span>
           </button>
         </div>
+
+        <!-- Suggested dev dependency install command -->
+        <template v-if="devDependencySuggestion.recommended">
+          <div class="flex items-center gap-2 pt-1 select-none">
+            <span class="text-fg-subtle font-mono text-sm"
+              ># {{ $t('package.get_started.dev_dependency_hint') }}</span
+            >
+          </div>
+          <div
+            v-for="pm in packageManagers"
+            :key="`install-dev-${pm.id}`"
+            :data-pm-cmd="pm.id"
+            class="flex items-center gap-2 group/devinstallcmd min-w-0"
+          >
+            <span class="text-fg-subtle font-mono text-sm select-none shrink-0">$</span>
+            <code class="font-mono text-sm min-w-0"
+              ><span
+                v-for="(part, i) in getDevInstallPartsForPM(pm.id)"
+                :key="i"
+                :class="i === 0 ? 'text-fg' : 'text-fg-muted'"
+                >{{ i > 0 ? ' ' : '' }}{{ part }}</span
+              ></code
+            >
+            <ButtonBase
+              type="button"
+              size="small"
+              class="text-fg-muted bg-bg-subtle/80 border-border opacity-0 group-hover/devinstallcmd:opacity-100 active:scale-95 focus-visible:opacity-100 select-none"
+              :aria-label="$t('package.get_started.copy_dev_command')"
+              @click.stop="copyDevInstallCommand"
+            >
+              <span aria-live="polite">{{
+                devInstallCopied ? $t('common.copied') : $t('common.copy')
+              }}</span>
+            </ButtonBase>
+          </div>
+        </template>
 
         <!-- @types package install - render all PM variants when types package exists -->
         <template v-if="typesPackageName && showTypesInInstall">

app/composables/usePackageAnalysis.ts

···
 import type { ModuleFormat, TypesStatus, CreatePackageInfo } from '#shared/utils/package-analysis'
+import type { DevDependencySuggestion } from '#shared/utils/dev-dependency'
 
 export interface PackageAnalysisResponse {
   package: string
   version: string
   moduleFormat: ModuleFormat
   types: TypesStatus
+  devDependencySuggestion: DevDependencySuggestion
   engines?: {
     node?: string
     npm?: string

app/pages/package/[[org]]/[name].vue

···
             :requested-version="requestedVersion"
             :install-version-override="installVersionOverride"
             :jsr-info="jsrInfo"
+            :dev-dependency-suggestion="packageAnalysis?.devDependencySuggestion"
             :types-package-name="typesPackageName"
             :executable-info="executableInfo"
             :create-package-info="createPackageInfo"

app/utils/install-command.ts

···
   packageManager: PackageManagerId
   version?: string | null
   jsrInfo?: JsrPackageInfo | null
+  dev?: boolean
+}
+
+export function getDevDependencyFlag(packageManager: PackageManagerId): '-D' | '-d' {
+  return packageManager === 'bun' ? '-d' : '-D'
 }
 
 /**
···
 
   const spec = getPackageSpecifier(options)
   const version = options.version ? `@${options.version}` : ''
+  const devFlag = options.dev ? [getDevDependencyFlag(options.packageManager)] : []
 
-  return [pm.label, pm.action, `${spec}${version}`]
+  return [pm.label, pm.action, ...devFlag, `${spec}${version}`]
 }
 
 export interface ExecuteCommandOptions extends InstallCommandOptions {

i18n/locales/en.json

···
       "title": "Get started",
       "pm_label": "Package manager",
       "copy_command": "Copy install command",
+      "copy_dev_command": "Copy dev install command",
+      "dev_dependency_hint": "Usually installed as a dev dependency",
       "view_types": "View {package}"
     },
     "create": {

i18n/locales/pl-PL.json

···
       "title": "Zacznij",
       "pm_label": "Menedżer pakietów",
       "copy_command": "Kopiuj komendę instalacji",
+      "copy_dev_command": "Kopiuj komendę instalacji dla dev",
+      "dev_dependency_hint": "Zazwyczaj instalowane jako zależność deweloperska",
       "view_types": "Zobacz {package}"
     },
     "create": {

i18n/schema.json

···
             "copy_command": {
               "type": "string"
             },
+            "copy_dev_command": {
+              "type": "string"
+            },
+            "dev_dependency_hint": {
+              "type": "string"
+            },
             "view_types": {
               "type": "string"
             }

lunaria/files/en-GB.json

···
       "title": "Get started",
       "pm_label": "Package manager",
       "copy_command": "Copy install command",
+      "copy_dev_command": "Copy dev install command",
+      "dev_dependency_hint": "Usually installed as a dev dependency",
       "view_types": "View {package}"
     },
     "create": {

lunaria/files/en-US.json

···
       "title": "Get started",
       "pm_label": "Package manager",
       "copy_command": "Copy install command",
+      "copy_dev_command": "Copy dev install command",
+      "dev_dependency_hint": "Usually installed as a dev dependency",
       "view_types": "View {package}"
     },
     "create": {

lunaria/files/pl-PL.json

···
       "title": "Zacznij",
       "pm_label": "Menedżer pakietów",
       "copy_command": "Kopiuj komendę instalacji",
+      "copy_dev_command": "Kopiuj komendę instalacji dla dev",
+      "dev_dependency_hint": "Zazwyczaj instalowane jako zależność deweloperska",
       "view_types": "Zobacz {package}"
     },
     "create": {

server/api/registry/analysis/[...pkg].get.ts

···
   hasBuiltInTypes,
 } from '#shared/utils/package-analysis'
 import {
+  getDevDependencySuggestion,
+  type DevDependencySuggestion,
+} from '#shared/utils/dev-dependency'
+import {
   NPM_REGISTRY,
   CACHE_MAX_AGE_ONE_DAY,
   ERROR_PACKAGE_ANALYSIS_FAILED,
···
 import { encodePackageName } from '#shared/utils/npm'
 import { getLatestVersion, getLatestVersionBatch } from 'fast-npm-meta'
 
+interface AnalysisPackageJson extends ExtendedPackageJson {
+  readme?: string
+}
+
 export default defineCachedEventHandler(
   async event => {
     // Parse package name and optional version from path
···
       // Fetch package data
       const encodedName = encodePackageName(packageName)
       const versionSuffix = version ? `/${version}` : '/latest'
-      const pkg = await $fetch<ExtendedPackageJson>(
+      const pkg = await $fetch<AnalysisPackageJson>(
         `${NPM_REGISTRY}/${encodedName}${versionSuffix}`,
       )
 
···
       const createPackage = await findAssociatedCreatePackage(packageName, pkg)
 
       const analysis = analyzePackage(pkg, { typesPackage, createPackage })
+      const devDependencySuggestion = getDevDependencySuggestion(packageName, pkg.readme)
 
       return {
         package: packageName,
         version: pkg.version ?? version ?? 'latest',
+        devDependencySuggestion,
         ...analysis,
       } satisfies PackageAnalysisResponse
     } catch (error: unknown) {
···
     swr: true,
     getKey: event => {
       const pkg = getRouterParam(event, 'pkg') ?? ''
-      return `analysis:v1:${pkg.replace(/\/+$/, '').trim()}`
+      return `analysis:v2:${pkg.replace(/\/+$/, '').trim()}`
     },
   },
 )
···
 export interface PackageAnalysisResponse extends PackageAnalysis {
   package: string
   version: string
+  devDependencySuggestion: DevDependencySuggestion
 }

shared/utils/dev-dependency.ts

···
+export type DevDependencySuggestionReason = 'known-package' | 'readme-hint'
+
+export interface DevDependencySuggestion {
+  recommended: boolean
+  reason?: DevDependencySuggestionReason
+}
+
+const KNOWN_DEV_DEPENDENCY_PACKAGES = new Set<string>([
+  'biome',
+  'chai',
+  'eslint',
+  'esbuild',
+  'husky',
+  'jest',
+  'lint-staged',
+  'mocha',
+  'oxc',
+  'oxfmt',
+  'oxlint',
+  'playwright',
+  'prettier',
+  'rolldown',
+  'rollup',
+  'stylelint',
+  'ts-jest',
+  'ts-node',
+  'tsx',
+  'turbo',
+  'typescript',
+  'vite',
+  'vitest',
+  'webpack',
+])
+
+const KNOWN_DEV_DEPENDENCY_PACKAGE_PREFIXES = [
+  '@typescript-eslint/',
+  'eslint-',
+  'prettier-',
+  'vite-',
+  'webpack-',
+  'babel-',
+]
+
+function isKnownDevDependencyPackage(packageName: string): boolean {
+  const normalized = packageName.toLowerCase()
+  if (normalized.startsWith('@types/')) {
+    return true
+  }
+  // Match scoped packages by name segment, e.g. @scope/eslint-config
+  const namePart = normalized.includes('/') ? normalized.split('/').pop() : normalized
+  if (!namePart) return false
+
+  return (
+    KNOWN_DEV_DEPENDENCY_PACKAGES.has(normalized) ||
+    KNOWN_DEV_DEPENDENCY_PACKAGES.has(namePart) ||
+    KNOWN_DEV_DEPENDENCY_PACKAGE_PREFIXES.some(prefix =>
+      prefix.startsWith('@') ? normalized.startsWith(prefix) : namePart.startsWith(prefix),
+    )
+  )
+}
+
+function escapeRegExp(text: string): string {
+  return text.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')
+}
+
+function hasReadmeDevInstallHint(packageName: string, readmeContent?: string | null): boolean {
+  if (!readmeContent) return false
+
+  const escapedName = escapeRegExp(packageName)
+  const escapedNpmName = escapeRegExp(`npm:${packageName}`)
+  const packageSpec = `(?:${escapedName}|${escapedNpmName})(?:@[\\w.-]+)?`
+
+  const patterns = [
+    // npm install -D pkg / pnpm add --save-dev pkg
+    new RegExp(
+      String.raw`(?:npm|pnpm|yarn|bun|vlt)\s+(?:install|add|i)\s+(?:--save-dev|--dev|-d)\s+${packageSpec}`,
+      'i',
+    ),
+    // npm install pkg --save-dev / pnpm add pkg -D
+    new RegExp(
+      String.raw`(?:npm|pnpm|yarn|bun|vlt)\s+(?:install|add|i)\s+${packageSpec}\s+(?:--save-dev|--dev|-d)`,
+      'i',
+    ),
+    // deno add -D npm:pkg
+    new RegExp(String.raw`deno\s+add\s+(?:--dev|-D)\s+${packageSpec}`, 'i'),
+  ]
+
+  return patterns.some(pattern => pattern.test(readmeContent))
+}
+
+export function getDevDependencySuggestion(
+  packageName: string,
+  readmeContent?: string | null,
+): DevDependencySuggestion {
+  if (isKnownDevDependencyPackage(packageName)) {
+    return {
+      recommended: true,
+      reason: 'known-package',
+    }
+  }
+
+  if (hasReadmeDevInstallHint(packageName, readmeContent)) {
+    return {
+      recommended: true,
+      reason: 'readme-hint',
+    }
+  }
+
+  return { recommended: false }
+}

test/unit/app/utils/install-command.spec.ts

···
   getPackageSpecifier,
   getExecuteCommand,
   getExecuteCommandParts,
+  getDevDependencyFlag,
 } from '../../../../app/utils/install-command'
 import type { JsrPackageInfo } from '../../../../shared/types/jsr'
 
···
       })
     })
 
+    describe('dev dependency installs', () => {
+      it.each([
+        ['npm', 'npm install -D eslint'],
+        ['pnpm', 'pnpm add -D eslint'],
+        ['yarn', 'yarn add -D eslint'],
+        ['bun', 'bun add -d eslint'],
+        ['deno', 'deno add -D npm:eslint'],
+        ['vlt', 'vlt install -D eslint'],
+      ] as const)('%s → %s', (pm, expected) => {
+        expect(
+          getInstallCommand({
+            packageName: 'eslint',
+            packageManager: pm,
+            jsrInfo: jsrNotAvailable,
+            dev: true,
+          }),
+        ).toBe(expected)
+      })
+    })
+
     describe('scoped package on JSR without version', () => {
       it.each([
         ['npm', 'npm install @trpc/server'],
···
       expect(parts).toEqual(['npm', 'install', 'lodash@4.17.21'])
     })
 
+    it('returns correct parts for npm with dev flag', () => {
+      const parts = getInstallCommandParts({
+        packageName: 'eslint',
+        packageManager: 'npm',
+        jsrInfo: jsrNotAvailable,
+        dev: true,
+      })
+      expect(parts).toEqual(['npm', 'install', '-D', 'eslint'])
+    })
+
     it('returns correct parts for deno with jsr: prefix when available', () => {
       const parts = getInstallCommandParts({
         packageName: '@trpc/server',
···
       expect(parts).toEqual(['deno', 'add', 'jsr:@trpc/server'])
     })
 
+    it('returns correct parts for bun with lowercase dev flag', () => {
+      const parts = getInstallCommandParts({
+        packageName: 'eslint',
+        packageManager: 'bun',
+        jsrInfo: jsrNotAvailable,
+        dev: true,
+      })
+      expect(parts).toEqual(['bun', 'add', '-d', 'eslint'])
+    })
+
     it('returns correct parts for deno with npm: prefix when not on JSR', () => {
       const parts = getInstallCommandParts({
         packageName: 'lodash',
···
       const parts = getInstallCommandParts(options)
       const command = getInstallCommand(options)
       expect(parts.join(' ')).toBe(command)
+    })
+  })
+
+  describe('getDevDependencyFlag', () => {
+    it('returns lowercase flag only for bun', () => {
+      expect(getDevDependencyFlag('bun')).toBe('-d')
+      expect(getDevDependencyFlag('npm')).toBe('-D')
+      expect(getDevDependencyFlag('deno')).toBe('-D')
     })
   })
 

test/unit/shared/utils/dev-dependency.spec.ts

···
+import { describe, expect, it } from 'vitest'
+import { getDevDependencySuggestion } from '../../../../shared/utils/dev-dependency'
+
+describe('getDevDependencySuggestion', () => {
+  it('suggests dev dependency for known tooling packages', () => {
+    expect(getDevDependencySuggestion('eslint')).toEqual({
+      recommended: true,
+      reason: 'known-package',
+    })
+    expect(getDevDependencySuggestion('@types/node')).toEqual({
+      recommended: true,
+      reason: 'known-package',
+    })
+    expect(getDevDependencySuggestion('@typescript-eslint/parser')).toEqual({
+      recommended: true,
+      reason: 'known-package',
+    })
+  })
+
+  it('suggests dev dependency from README install command hints', () => {
+    const readme = '<p>Install with <code>npm install --save-dev some-tool</code></p>'
+
+    expect(getDevDependencySuggestion('some-tool', readme)).toEqual({
+      recommended: true,
+      reason: 'readme-hint',
+    })
+  })
+
+  it('suggests dev dependency from README --dev flag hints', () => {
+    const readme = '<p><code>yarn add --dev some-tool</code></p>'
+
+    expect(getDevDependencySuggestion('some-tool', readme)).toEqual({
+      recommended: true,
+      reason: 'readme-hint',
+    })
+  })
+
+  it('suggests dev dependency from README deno -D hints', () => {
+    const readme = '<p><code>deno add -D npm:some-tool</code></p>'
+
+    expect(getDevDependencySuggestion('some-tool', readme)).toEqual({
+      recommended: true,
+      reason: 'readme-hint',
+    })
+  })
+
+  it('does not suggest dev dependency for runtime packages without hints', () => {
+    expect(getDevDependencySuggestion('react')).toEqual({
+      recommended: false,
+    })
+  })
+
+  it('does not suggest when README hint targets a different package', () => {
+    const readme = '<p>Install with <code>yarn add -D bar</code></p>'
+
+    expect(getDevDependencySuggestion('foo', readme)).toEqual({
+      recommended: false,
+    })
+  })
+})