incorrect-keyword-case (S233)

Fix is always available.

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What it does

Checks that Fortran keywords use a consistent casing style. Flags any keyword whose casing does not match the configured style (see keyword-case).

Fortran is case-insensitive, so keyword casing is purely a stylistic choice. However, inconsistent casing — mixing IMPLICIT NONE, implicit none, and Implicit None in the same codebase — reduces readability and makes code harder to scan. Enforcing a consistent style helps maintain a uniform appearance across the codebase.

Modern Fortran style guides generally favour lowercase keywords. Older codebases often use uppercase, inherited from fixed-form Fortran conventions.

Examples

With keyword-case = "lowercase":

Incorrect

IMPLICIT NONE
INTEGER, INTENT(IN) :: x
END SUBROUTINE foo

Correct

implicit none
integer, intent(in) :: x
end subroutine foo

With keyword-case = "uppercase":

Incorrect

implicit none
integer, intent(in) :: x
end subroutine foo

Correct

IMPLICIT NONE
INTEGER, INTENT(IN) :: x
END SUBROUTINE foo