🔥 Feature: migrate redirect and rewrite Rules maps to RuleList

[ReneWerner87]

Description

Draft, because it depends on two fiber PRs that are still open: gofiber/fiber#4621 (redirect) and gofiber/fiber#4633 (rewrite). Both deprecate Rules map[string]string in favour of an ordered RuleList []Rule, and both keep the map working for the whole of v3, so nothing here is urgent. Ready to un-draft once they land.

One migration serves both middlewares: the new field is spelled the same in each and the reason for the deprecation is the same.

// Before
redirect.New(redirect.Config{
    Rules: map[string]string{
        "/api/*":     "/v2/$1",
        "/api/users": "/v2/users",
    },
})

// After
redirect.New(redirect.Config{
    RuleList: []redirect.Rule{
        {From: "/api/users", To: "/v2/users"},
        {From: "/api/*", To: "/v2/$1"},
    },
})

The ordering is the point

Note which rule comes first above. The entries are emitted in the order the deprecated map ranked them, not the order they were written.

A map has no order, so the middleware sorted its keys: most path text before the first *, then most path text overall, then fewest asterisks, then the key. A RuleList is tried top to bottom. Copying the source order across would therefore be a silent behaviour change for any config that happened to spell a catch-all above something it also matches, which is exactly the case a user is least likely to notice. sortRules reproduces the middleware's ranking so each path is answered the way it was before.

What it does not touch

A Rules value this cannot read verbatim is left alone rather than guessed at, and prints nothing:

• a variable instead of a literal, Rules: rules
• a computed value, "/old": target
• another package's Config that happens to have a Rules field

All three still compile against the deprecated field, which is a better outcome than a wrong rewrite. Comments and blank lines inside the map are skipped; anything else in there stops the rewrite for that block.

Import aliases are honoured, so rd "github.com/gofiber/fiber/v3/middleware/redirect" emits []rd.Rule.

Registration

Its own range, inside v3 only:

{
    From: ">=3.6.0-0",
    To:   "<4.0.0-0",
    Functions: []MigrationFn{v3migrations.MigrateRuleList},
}

RuleList lands in 3.6.0 and Rules keeps working beside it for the rest of v3, so that is the band where this applies. Test_DoMigration_RuleListRunsWithinV3From36 pins it: 3.6.0 and later within v3 migrate, 3.5.0 and a v2 origin do not, and a 4.0.0 target does not.

It is idempotent, so a repeat run reports nothing.

Tests

Test_MigrateRuleList_* covers redirect, rewrite, the ranking (asserting the specific rule is emitted above the catch-all), import aliases, the three shapes it declines, and idempotency. Full suite passes.