🐛 `fiber migrate` produces invalid code for filesystem middleware migration

[CybotTM]

Bug Description

The fiber migrate --to v3.0.0 command produces invalid Go code when migrating the filesystem middleware to the new static middleware.

Issues Found

1. Invalid os.DirFS() usage with http.FS()

The migration tool generates:

app.Use("/static", static.New("", static.Config{
    FS:     os.DirFS(http.FS(embedFS)),
    MaxAge: 24 * 60 * 60,
}))

This is invalid because http.FS() returns http.FileSystem, not a string path that os.DirFS() expects.

Correct code should be:

app.Use("/static", static.New("", static.Config{
    FS:     embedFS,  // embed.FS implements fs.FS directly
    MaxAge: 24 * 60 * 60,
}))

2. Import naming conflict

When a project has its own package named static (e.g., internal/web/static for embedded assets), the migration tool imports github.com/gofiber/fiber/v3/middleware/static without aliasing, causing a naming conflict:

import (
    "github.com/gofiber/fiber/v3/middleware/static"
    "myproject/internal/web/static"  // Conflict!
)

Steps to Reproduce

1. Create a Fiber v2 project with:

   • An embedded filesystem using embed.FS
   • A package named static (e.g., internal/web/static)
   • Usage of filesystem.New() middleware

2. Run fiber migrate --to v3.0.0

3. Observe the generated code fails to compile

Expected Behavior

The migration tool should:

1. Recognize that embed.FS already implements fs.FS and use it directly
2. Detect naming conflicts and add an alias (e.g., staticmw "github.com/gofiber/fiber/v3/middleware/static")

Environment

• Fiber CLI version: v0.11.3
• Go version: 1.25.7
• OS: Linux

Original Code (v2)

import (
    "net/http"
    "github.com/gofiber/fiber/v2/middleware/filesystem"
    "myproject/internal/web/static"
)

app.Use("/static", filesystem.New(filesystem.Config{
    Root:   http.FS(static.Static),
    MaxAge: 24 * 60 * 60,
}))

Generated Code (broken)

import (
    "os"
    "net/http"
    "github.com/gofiber/fiber/v3/middleware/static"
    "myproject/internal/web/static"  // CONFLICT
)

app.Use("/static", static.New("", static.Config{
    FS:     os.DirFS(http.FS(static.Static)),  // INVALID
    MaxAge: 24 * 60 * 60,
}))

Correct Code (manual fix)

import (
    "github.com/gofiber/fiber/v3/middleware/static"
    webstatic "myproject/internal/web/static"  // Aliased
)

app.Use("/static", static.New("", static.Config{
    FS:     webstatic.Static,  // Direct use of embed.FS
    MaxAge: 24 * 60 * 60,
}))

[coderabbitai]

🔗 Related PRs

gofiber/fiber#3006 - middleware: add static middleware [merged]
gofiber/fiber#3673 - 🐛 bug: Fix Static middleware browser support for subdirectories [merged]
gofiber/fiber#3688 - 🐛 bug: Handle invalid path in filesystem [merged]
#165 - Fix Add migration and import handling [merged]
#234 - Migrate filesystem middleware to static middleware [merged]

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💬 Have feedback or questions? Drop into our discord!

[ReneWerner87]

thx for this report
i will check in some minutes

[ReneWerner87]

@CybotTM can you verify the fix with https://github.com/gofiber/cli/releases/tag/v0.11.4

[CybotTM]

@ReneWerner87 Verified! ✅

Tested v0.11.4 on a real Fiber v2 codebase:

# Install the fixed CLI
$ go install github.com/gofiber/cli/fiber@v0.11.4

$ fiber version
fiber version: v3.0.0 (latest 3.0.0)
fiber cli version: 0.11.4 (latest 0.11.4)

# Clone a real v2 project to test
$ git clone https://github.com/netresearch/ldap-selfservice-password-changer test-repo
$ cd test-repo
$ git checkout a9fd9f7  # Pure Fiber v2.52.11, no v3

# Run migration
$ fiber migrate
Migrating Go packages
Migrating handler signatures
Migrating parser methods
Migrating listener related config fields
Migrating filesystem middleware
Ensuring go version >= 1.25.0
Migration from Fiber 2.52.11 to 3.0.0

# Build assets (project-specific)
$ pnpm install && pnpm build:assets

# Verify build
$ go build -o /tmp/test-app .
# ✅ Build successful

# Run tests on Fiber-related code
$ go test -short ./internal/rpc/...
ok  	github.com/netresearch/ldap-selfservice-password-changer/internal/rpc	0.006s
# ✅ All RPC tests pass (these use fiber.Ctx)

# Verify app runs
$ /tmp/test-app --help
# ✅ Shows help correctly

Migration correctly transformed:

• Imports from fiber/v2 to fiber/v3
• *fiber.Ctx to fiber.Ctx (interface change)
• c.BodyParser() to c.Bind().Body() (API change)

Thanks for merging the fix quickly! 🎉