[spec] Define the syntax of exact heap types

document/core/syntax/types.rst

@@ -110,6 +110,7 @@ $${syntax: {absheaptype/syn heaptype}}
 
 A heap type is either *abstract* or *concrete*.
 A concrete heap type consists of a :ref:`type use <syntax-typeuse>` that classifies an object of the respective :ref:`type <syntax-type>` defined in a module.
+A concrete heap type may be *exact*, in which case it classifies objects of precisely the respective :ref:`type <syntax-type>` and not any other type that may :ref:`match <match-heaptype>` it.
 Abstract types are denoted by individual keywords.
 
 The type ${:FUNC} denotes the common supertype of all :ref:`function types <syntax-functype>`, regardless of their concrete definition.

document/core/util/macros.def

@@ -238,6 +238,7 @@
 .. |REF| mathdef:: \xref{syntax/types}{syntax-reftype}{\K{ref}}
 .. |NULL| mathdef:: \xref{syntax/types}{syntax-reftype}{\K{null}}
 
+.. |EXACT| mathdef:: \xref{syntax/types}{syntax-heaptype}{\K{exact}}
 .. |ANY| mathdef:: \xref{syntax/types}{syntax-heaptype}{\K{any}}
 .. |EQT| mathdef:: \xref{syntax/types}{syntax-heaptype}{\K{eq}}
 .. |I31| mathdef:: \xref{syntax/types}{syntax-heaptype}{\K{i\scriptstyle31}}

specification/wasm-latest/1.2-syntax.types.spectec

@@ -41,7 +41,7 @@ syntax typevar hint(desc "type variable") =
   | _IDX typeidx | REC n hint(show REC.%)
 
 syntax heaptype hint(desc "heap type") =
-  | absheaptype | typeuse
+  | absheaptype | typeuse | EXACT typeuse
 
 syntax reftype hint(desc "reference type") =
   | REF null? heaptype