Bug: mage tab completion breaks for namespaced targets (zsh)

[alexchebaturkin]

Bug Description
When running mage <TAB> against magefiles that have mg.Namespace defined, mage completion incorrectly handles : in the target names, e.g. :

> mage -l
Targets:
  fmt                   formats Go code using gofmt.
  migration:create      creates a timestamped SQL migration.
  migration:down        rolls back one migration.
  migration:status      prints migration status.
  migration:up          applies pending migrations.
  migration:validate    validates migration files without changing a database.
  sqlc:diff             reports whether generated query code differs from checked-in code.
  sqlc:generate         regenerates database query code from migrations and named queries.
  sqlc:vet              checks SQL queries for errors.

> mage <TAB>
migration  -- create
sqlc       -- diff
build     checkfmt  ci        clean     fix       fmt       install   lint      test      vet

What did you do?

type Migration mg.Namespace

func (Migration) Create() {}
func (Migration) Down() {}
func (Migration) Up() {}
...

What did you expect to happen?

I was expecting tab completion to produce this instead (newlines vs. spaces notwithstanding):

> mage <TAB>
migration:create
migration:down
migration:status
migration:up
migration:validate
sqlc:diff
sqlc:generate
sqlc:vet
build     checkfmt  ci        clean     fix       fmt       install   lint      test      vet

What actually happened?

The first target of each mg.Namespace becomes the zsh description of that namespace. All the other targets are dropped. When you type mage migration:cr<TAB>, it doesn't complete it either:

> mage <TAB>
migration  -- create
sqlc       -- diff
build     checkfmt  ci        clean     fix       fmt       install   lint      test      vet

Environment

• Mage Version:

Mage Build Tool v1.17.2
Build Date: 2026-04-22T22:57:48Z
Commit: 0953947c1673fd745a51c032aadeb3c63f9f3368
built with: go1.26.2

• OS: macOS

Additional context
I've only tested this in zsh, but let me know if you want me to provide examples for bash,fish etc.

[DavidGamba]

Mage doesn't use Go to manage its completion but this might be helpful for someone digging into the issue:

I have run into this in my own tooling[1][2].
First, there is no reliable way to determine if you are in bash or in zsh so you have to ask your users to help you out. I do it by asking zsh users to set export ZSHELL="true" [1].

Second, bash completions have dividers and once you encounter the divider, you only provide completion results for the part after the divider. You don't need to do that in zsh.
This is my convoluted completion logic[2]

[1] https://github.com/DavidGamba/go-getoptions/tree/d9222021aaac09a7860236777bc8a57e3d4fb6ae#autocompletion

[2] https://github.com/DavidGamba/go-getoptions/blob/d9222021aaac09a7860236777bc8a57e3d4fb6ae/user.go#L306-L349