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[flang] Allow empty SEQUENCE types #66252

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Merged
merged 1 commit into from
Sep 18, 2023
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[flang] Allow empty SEQUENCE types #66252

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3 changes: 3 additions & 0 deletions flang/docs/Extensions.md
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Expand Up @@ -428,6 +428,9 @@ end
* Since Fortran 90, INCLUDE lines have been allowed to have
a numeric kind parameter prefix on the file name. No other
Fortran compiler supports them that I can find.
* A `SEQUENCE` derived type is required (F'2023 C745) to have
at least one component. No compiler enforces this constraint;
this compiler emits a warning.

## Behavior in cases where the standard is ambiguous or indefinite

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5 changes: 3 additions & 2 deletions flang/lib/Semantics/resolve-names.cpp
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Expand Up @@ -5225,9 +5225,10 @@ bool DeclarationVisitor::Pre(const parser::DerivedTypeDef &x) {
Walk(componentDefs);
if (derivedTypeInfo_.sequence) {
details.set_sequence(true);
if (componentDefs.empty()) { // C740
if (componentDefs.empty()) {
// F'2023 C745 - not enforced by any compiler
Say(stmt.source,
"A sequence type must have at least one component"_err_en_US);
"A sequence type should have at least one component"_warn_en_US);
}
if (!details.paramNames().empty()) { // C740
Say(stmt.source,
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2 changes: 1 addition & 1 deletion flang/test/Semantics/resolve31.f90
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Expand Up @@ -68,7 +68,7 @@ module m4
!ERROR: A sequence type may not have a CONTAINS statement
contains
end type
!ERROR: A sequence type must have at least one component
!WARNING: A sequence type should have at least one component
type :: emptyType
sequence
end type emptyType
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