fix(migrate): keep bun catalog specs when workspaces.packages is empty

crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_bun_old_no_top_level_catalog/package.json

@@ -0,0 +1,14 @@
+{
+  "name": "migration-bun-old-no-top-level-catalog",
+  "workspaces": [],
+  "devDependencies": {
+    "vite": "^7.0.0"
+  },
+  "devEngines": {
+    "packageManager": {
+      "name": "bun",
+      "version": "1.2.20",
+      "onFail": "download"
+    }
+  }
+}

crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_bun_old_no_top_level_catalog/snapshots.toml

@@ -0,0 +1,9 @@
+[[case]]
+name = "migration_bun_old_no_top_level_catalog"
+vp = "global"
+comment = "Bun before 1.2.21 reads only `workspaces.catalog`, so a top-level `catalog` would fail to resolve."
+steps = [
+  { argv = ["vp", "migrate", "--no-interactive"], comment = "an empty-workspaces bun 1.2.20 project without Vite+ migrates", continue-on-failure = true },
+  { argv = ["vpt", "print-file", "package.json"], comment = "toolchain specs stay concrete and no top-level catalog is written", continue-on-failure = true },
+  { argv = ["vp", "migrate", "--no-interactive"], comment = "a second run converges to the already-migrated fast exit", continue-on-failure = true },
+]

crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_bun_old_no_top_level_catalog/snapshots/migration_bun_old_no_top_level_catalog.md

@@ -0,0 +1,53 @@
+# migration_bun_old_no_top_level_catalog
+
+Bun before 1.2.21 reads only `workspaces.catalog`, so a top-level `catalog` would fail to resolve.
+
+## `vp migrate --no-interactive`
+
+an empty-workspaces bun 1.2.20 project without Vite+ migrates
+
+```
+VITE+ - The Unified Toolchain for the Web
+
+◇ Migrated . to Vite+ <version>
+• Node <version>  bun <version>
+• 2 config updates applied
+```
+
+## `vpt print-file package.json`
+
+toolchain specs stay concrete and no top-level catalog is written
+
+```
+{
+  "name": "migration-bun-old-no-top-level-catalog",
+  "workspaces": [],
+  "devDependencies": {
+    "vite": "npm:@voidzero-dev/vite-plus-core@<version>",
+    "vite-plus": "<version>"
+  },
+  "devEngines": {
+    "packageManager": {
+      "name": "bun",
+      "version": "<version>",
+      "onFail": "download"
+    }
+  },
+  "overrides": {
+    "vite": "npm:@voidzero-dev/vite-plus-core@<version>"
+  },
+  "scripts": {
+    "prepare": "vp config"
+  }
+}
+```
+
+## `vp migrate --no-interactive`
+
+a second run converges to the already-migrated fast exit
+
+```
+VITE+ - The Unified Toolchain for the Web
+
+This project is already using Vite+! Happy coding!
+```

crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_upgrade_bun_empty_workspaces_catalog/package.json

@@ -0,0 +1,25 @@
+{
+  "name": "migration-upgrade-bun-empty-workspaces-catalog",
+  "devDependencies": {
+    "vite-plus": "catalog:",
+    "vitest": "catalog:"
+  },
+  "overrides": {
+    "vite": "catalog:",
+    "vitest": "catalog:"
+  },
+  "devEngines": {
+    "packageManager": {
+      "name": "bun",
+      "version": "1.4.0",
+      "onFail": "download"
+    }
+  },
+  "workspaces": {
+    "packages": [],
+    "catalog": {
+      "vite-plus": "^0.1.20",
+      "vitest": "4.1.9"
+    }
+  }
+}

crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_upgrade_bun_empty_workspaces_catalog/snapshots.toml

@@ -0,0 +1,9 @@
+[[case]]
+name = "migration_upgrade_bun_empty_workspaces_catalog"
+vp = "global"
+comment = "Bun resolves catalogs whenever the root package.json has a `workspaces` field, even with an empty package list (#3375)."
+steps = [
+  { argv = ["vp", "migrate", "--no-interactive"], comment = "a single-package bun project with an empty workspaces.packages keeps its catalog", continue-on-failure = true },
+  { argv = ["vpt", "print-file", "package.json"], comment = "toolchain specs stay catalog: and the workspaces.catalog is rewritten in place", continue-on-failure = true },
+  { argv = ["vp", "migrate", "--no-interactive"], comment = "a second run converges to the already-migrated fast exit", continue-on-failure = true },
+]

crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_upgrade_bun_empty_workspaces_catalog/snapshots/migration_upgrade_bun_empty_workspaces_catalog.md

@@ -0,0 +1,59 @@
+# migration_upgrade_bun_empty_workspaces_catalog
+
+Bun resolves catalogs whenever the root package.json has a `workspaces` field, even with an empty package list (#3375).
+
+## `vp migrate --no-interactive`
+
+a single-package bun project with an empty workspaces.packages keeps its catalog
+
+```
+VITE+ - The Unified Toolchain for the Web
+
+◇ Updated . to Vite+ <version>
+• Node <version>  bun <version>
+• Dependencies:
+    vite-plus  0.1.20 → <version>
+    vite              → <version>
+• Package manager settings configured
+```
+
+## `vpt print-file package.json`
+
+toolchain specs stay catalog: and the workspaces.catalog is rewritten in place
+
+```
+{
+  "name": "migration-upgrade-bun-empty-workspaces-catalog",
+  "devDependencies": {
+    "vite": "catalog:",
+    "vite-plus": "catalog:"
+  },
+  "overrides": {
+    "vite": "catalog:"
+  },
+  "devEngines": {
+    "packageManager": {
+      "name": "bun",
+      "version": "<version>",
+      "onFail": "download"
+    }
+  },
+  "workspaces": {
+    "packages": [],
+    "catalog": {
+      "vite-plus": "<version>",
+      "vite": "npm:@voidzero-dev/vite-plus-core@<version>"
+    }
+  }
+}
+```
+
+## `vp migrate --no-interactive`
+
+a second run converges to the already-migrated fast exit
+
+```
+VITE+ - The Unified Toolchain for the Web
+
+This project is already using Vite+! Happy coding!
+```

docs/guide/migrate-rules.md

@@ -398,7 +398,9 @@ Migration converts the Volta `volta.node` pin to `.node-version`, because Vite+
 
 ### Bun
 
-- Bun catalogs only resolve inside a workspace (a root `package.json` with a non-empty `workspaces`). In a bun workspace, existing top-level or workspace catalog locations and named catalog references are preserved. A standalone (single-package) bun project keeps concrete specs and gets no catalog field, because `bun install` cannot resolve `catalog:` outside a workspace.
+- Bun catalogs only resolve inside a workspace, which is a root `package.json` with a `workspaces` field. An empty `workspaces` field also counts. In a bun workspace, existing top-level or workspace catalog locations and named catalog references are preserved. A standalone bun project without `workspaces` keeps concrete specs and gets no catalog field, because `bun install` cannot resolve `catalog:` outside a workspace.
+- Bun before 1.2.21 reads only catalogs under `workspaces`. On those versions, migration uses catalogs only when the project already has one under `workspaces`, and keeps concrete specs otherwise.
+- When an existing named catalog already owns `vite-plus`, `vite`, or `vitest`, migration adds missing toolchain entries to that catalog instead of creating a default catalog beside it.
 - The core alias is mirrored as a direct `vite` dependency so Bun sees the peer provider before applying overrides.
 
 ## After the Migration

packages/cli/src/migration/__tests__/bun-catalog-file-protocol.spec.ts

@@ -114,8 +114,8 @@ describe('rewriteMonorepo bun catalog with file: protocol', () => {
       overrides: Record<string, string>;
       devDependencies: Record<string, string>;
     };
-    expect(pkg.workspaces.catalog.vite).toBeUndefined();
-    expect(pkg.workspaces.catalog.vitest).toBeUndefined();
+    expect(pkg.workspaces.catalog?.vite).toBeUndefined();
+    expect(pkg.workspaces.catalog?.vitest).toBeUndefined();
     expect(pkg.workspaces.catalogs.build.vite).toBe('^7.0.0');
     expect(pkg.workspaces.catalogs.build.vitest).toBe('^4.0.0');
     expect(pkg.workspaces.catalogs.build.tsdown).toBeUndefined();