Repairs — `miri fix`

A repair is an edit the compiler is sure of. When a diagnostic carries one, miri fix can write it. Without --apply it only shows what it would do:

$ miri fix tally.mi
tally.mi:9:18 [MER_PAR_020]
  '&&' is not a valid operator in Miri
  repair word-operator: Write `&&` as `and`.
    replace `&&` with `and` at 219
exit status 0

miri fix FILE --apply --yes writes every repair in the file in one go. (--yes confirms the write when there is no terminal to ask at, which is always the case for an agent.)

How safe is a repair?

Every diagnostic code has a fixSafety level. miri fix --apply writes the first three on its own and refuses the rest unless you add --allow-risky:

Level	Meaning	Applied by default
`format-only`	Changes layout only.	yes
`behavior-preserving`	Changes the text, not what the program does.	yes
`local-edit`	Changes one spot, and nothing outside it can notice.	yes
`api-changing`	Changes something other code relies on, such as a parameter name callers can pass by name.	no
`target-changing`	Changes where or how the program runs, such as moving data to the GPU or narrowing a number.	no
`requires-human-review`	Plausible, but a person should look first.	no

Every repair

The list the miri-lang pack carries, with the diagnostic codes that can offer each repair:

Repair	What it does	Offered with
`add-import`	Import a name that resolves in exactly one module.	`MER_TYP_034` `MER_TYP_043`
`arrow-return-type`	Drop the `->` before a return type.	`MER_PAR_001`
`cast-to-slot-type`	Convert a number with `as` to the width of the place it is stored; a value outside that width’s range is truncated or rounded.	`MER_TYP_002`
`colon-annotation`	Drop the `:` before a type annotation.	`MER_PAR_001`
`concat-to-formatted-string`	Rewrite a `+` chain joining text to values as one f-string.	`MER_TYP_002`
`drop-extra-arguments`	Drop positional arguments a call does not declare.	`MER_TYP_030`
`drop-iterator-accessor`	Drop a `keys` accessor on a keyed collection and iterate it directly.	`MER_TYP_033`
`if-colon`	Write `:` in place of `then`, or after an inline `else`.	`MER_PAR_001`
`interpolation-quotes`	Write the string literals inside an f-string’s braces with the other quote.	`MER_LEX_012`
`let-mut-to-var`	Rewrite a `let mut` binding as `var`.	`MER_PAR_001`
`let-to-var`	Rebind an immutable declaration as mutable.	`MER_TYP_042`
`move-into-main`	Move statements written beside `main` into it, in order, ahead of what it already does.	`MER_TYP_069`
`null-to-none`	Rewrite `null`, `nil` or `nullptr` as `None`.	`MER_TYP_034`
`println-bang`	Drop the `!` from a macro-style call.	`MER_LEX_001`
`qualify-variant-pattern`	Prefix a bare variant pattern with the enum that declares it.	`MER_TYP_038`
`remove-unused-import`	Delete a `use` line nothing reads, or the unread names in a selection.	`MER_IMP_005`
`rename-to-suggestion`	Rewrite a name as the one spelling the help offers in its place.	`MER_IMP_003` `MER_TYP_033` `MER_TYP_034` `MER_TYP_038` `MER_TYP_043`
`underscore-unread-binding`	Prefix a binding nothing reads with `_` to say the value is not meant to be read.	`MER_TYP_071` `MER_TYP_072`
`word-operator`	Rewrite `!`, `&&` or `\|\|` as `not`, `and` or `or`.	`MER_LEX_001` `MER_PAR_020`

Repairs — miri fix

How safe is a repair?

Every repair

Repairs — `miri fix`