Fix: correct function and variable naming in fish completion script

[TimSoethout]

This pull request updates the Fish shell autocomplete script to fix formatting and variable substitution issues, ensuring correct function naming and output formatting for command completions.

Improvements to autocomplete script:

• Renamed function and completion commands to use %[1]s instead of %[1], ensuring proper variable substitution for command names throughout the script (autocomplete/fish_autocomplete). [1] [2]
• Updated string matching and printf formatting to use the correct Fish and printf syntax, preventing formatting errors in completion output (autocomplete/fish_autocomplete).

What type of PR is this?

• bug

What this PR does / why we need it:

PR #2270 introduced dynamic fish completions but used invalid Go format specifiers in the fish autocomplete template. The format string %[1] was missing the type specifier s, causing fmt.Sprintf to produce malformed output like __%!_(string=appname)perform_completion instead of __appname_perform_completion.

Changes:

• autocomplete/fish_autocomplete: Fixed format specifiers from %[1] to %[1]s (7 occurrences). Also escaped %s as %%s in the printf statements so they remain literal in the generated fish script.

Which issue(s) this PR fixes:

Fixes #2285

Testing

• All existing tests pass
• New regression test TestCompletionFishFormat added
• Manually tested on fish 4.5.0:

./app completion fish | source # Sources without error
functions __app_perform_completion # Function exists
complete -c app # Completions registered

Release Notes

Fixed fish shell completion script generation that was broken due to invalid format specifiers (introduced in v3.7.0)

@TimSoethout assisted by copilot.

[Copilot]

Pull request overview

This PR fixes formatting issues in the Fish shell completion script template used by cli completion fish, correcting Go fmt.Sprintf placeholder usage so generated Fish functions/completions render with the expected command name and without %!-style formatting errors.

Changes:

• Updated Fish completion template placeholders from %[1] to %[1]s for correct Go string substitution.
• Escaped printf format verbs (%s → %%s) so they remain literal in the generated Fish script.

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