SIFR-MATCH-0004: Invalid or unsupported match pattern form. - Sifr

SIFR-MATCH-0004 belongs to the Pattern matching diagnostic family. It means: invalid or unsupported match pattern form.

Why It Happens

The pattern match cannot be proven valid. Check exhaustiveness, guard types, class-pattern fields, and supported pattern forms.

Use sifr --explain SIFR-MATCH-0004 locally to see the renderer’s exact message template and any machine-applicable suggestions for the compiler version you are running.

Erroneous Code

match value:
    case 0:
        label = "zero"

How To Fix It

Make patterns supported, guards boolean, field names valid, and matches exhaustive where required.

Fixed Code

match value:
    case 0:
        label = "zero"
    case _:
        label = "other"

Details

Field	Value
Code	`SIFR-MATCH-0004`
Family	`MATCH`
Severity	Error
Stability	stable
Owner	`sifr_lowering::lower::statements`
Representative fixture	`crates/sifr/tests/e2e/fail/match_tuple_pattern_requires_tuple_subject.sifr`

See the Error Codes index for the complete catalog.