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Merge pull request #1296 from vlstill/nesting-rules
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Clarify nesting rules
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@jonathan-dilorenzo
jonathan-dilorenzo authored Aug 6, 2024
2 parents da5a264 + a1e6086 commit f9189ae
Showing 1 changed file with 44 additions and 38 deletions.
82 changes: 44 additions & 38 deletions p4-16/spec/P4-16-spec.mdk
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Original file line number Diff line number Diff line change
Expand Up @@ -2516,27 +2516,27 @@ header unions, structs, tuples, and lists. Note that `int` by itself
arbitrary-precision integer, without a width specified.

|--------------------|------------------------------------------------|||||
| | Container type |||||
| | Container kind |||||
| |-----------|--------------|-----------------|------|--------------|
| Element type | header | header_union | struct or tuple | list | header stack |
+:-------------------+:----------+:-------------+:----------------+:-----+:-------------+
| `bit<W>` | allowed | error | allowed | allowed | error |
| `int<W>` | allowed | error | allowed | allowed | error |
| `varbit<W>` | allowed | error | allowed | allowed | error |
| `int` | error | error | error | allowed | error |
| `void` | error | error | error | error | error |
| `string` | error | error | error | allowed | error |
| `error` | error | error | allowed | allowed | error |
| `match_kind` | error | error | error | allowed | error |
| `bool` | allowed | error | allowed | allowed | error |
| `enum` | allowed[^enum_header] | error | allowed | allowed | error |
| `header` | error | allowed | allowed | allowed | allowed |
| header stack | error | error | allowed | allowed | error |
| `header_union` | error | error | allowed | allowed | allowed |
| `struct` | allowed[^struct_header] | error | allowed | allowed | error |
| `tuple` | error | error | allowed | allowed | error |
| `list` | error | error | error | allowed | error |
|----------------|-----------|---------|----------|---------|-------|
| `bit<W>` | allowed | error | allowed | allowed | error |
| `int<W>` | allowed | error | allowed | allowed | error |
| `varbit<W>` | allowed | error | allowed | allowed | error |
| `int` | error | error | error | allowed | error |
| `void` | error | error | error | error | error |
| `string` | error | error | error | allowed | error |
| `error` | error | error | allowed | allowed | error |
| `match_kind` | error | error | error | allowed | error |
| `bool` | allowed | error | allowed | allowed | error |
| enumeration types | allowed[^enum_header] | error | allowed | allowed | error |
| header types | error | allowed | allowed | allowed | allowed |
| header stacks | error | error | allowed | allowed | error |
| header unions | error | error | allowed | allowed | allowed |
| struct types | allowed[^struct_header] | error | allowed | allowed | error |
| tuple types | error | error | allowed | allowed | error |
| list types | error | error | error | allowed | error |
|--------------------|-----------|---------|----------|---------|-------|

[^enum_header]: an `enum` type used as a field in a `header` must specify a
underlying type and representation for `enum` elements.
Expand All @@ -2562,26 +2562,32 @@ The table below lists all types that may appear as base types in a
`typedef` or `type` declaration.


|------------------|--------------------|-----------------|
| Base type B | `typedef B <name>` | `type B <name>` |
+:-----------------+:-------------------+:----------------+
| `bit<W>` | allowed | allowed |
| `int<W>` | allowed | allowed |
| `varbit<W>` | allowed | error |
| `int` | allowed | error |
| `void` | error | error |
| `error` | allowed | error |
| `match_kind` | error | error |
| `bool` | allowed | allowed |
| `enum` | allowed | error |
| `header` | allowed | error |
| header stack | allowed | error |
| `header_union` | allowed | error |
| `struct` | allowed | error |
| `tuple` | allowed | error |
| a `typedef` name | allowed | allowed[^type_allowed] |
| a `type` name | allowed | allowed |
|------------------|--------------------|-----------------|
|-------------------|--------------------|-----------------|
| Base type B | `typedef B <name>` | `type B <name>` |
+:------------------+:-------------------+:----------------+
| `bit<W>` | allowed | allowed |
| `int<W>` | allowed | allowed |
| `varbit<W>` | allowed | error |
| `int` | allowed | error |
| `void` | error | error |
| `string` | allowed | error |
| `error` | allowed | error |
| `match_kind` | error | error |
| `bool` | allowed | allowed |
| enumeration types | allowed | error |
| header types | allowed | error |
| header stacks | allowed | error |
| header unions | allowed | error |
| struct types | allowed | error |
| tuple types | allowed | error |
| list types | allowed | error |
| a `typedef` name | allowed | allowed[^type_allowed] |
| a `type` name | allowed | allowed |
|-------------------|--------------------|-----------------|

Rationale: So far, no clear motivation for allowing `typedef` for `void`
and `match_kind` was presented. Therefore, to be on the safe side this
is disallowed.

[^type_allowed]: `type B <name>` is allowed for a type name `B`
defined via `typedef X B` if `type X <name>` is allowed.
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