grammar: Parse externs

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>

tree-sitter-p4/grammar.js

@@ -68,13 +68,16 @@ export default grammar({
         instantiation: $ => seq($.typeRef, '(', optional($.parameter_list), ')', $.identifier),
 
         // Declarations
-        declaration: $ => seq(choice($.parserDeclaration, $.parserTypeDeclaration, $.type_declaration, $.function_declaration, $.control_declaration)),
+        declaration: $ => seq(choice($.parserDeclaration, $.parserTypeDeclaration, $.type_declaration, $.function_declaration, $.control_declaration, $.extern_declaration)),
 
         type_declaration: $=> choice($.struct_declaration),
         struct_declaration: $ => seq($.struct, $.identifier, '{', optional($.struct_declaration_fields), '}'),
         struct_declaration_fields: $=> repeat1(seq($.variableDeclaration)),
 
-        function_declaration: $=> seq($.typeRef, $.identifier, $.parameters, $.statement),
+        extern_declaration: $=> seq($.extern, $.declaration),
+
+        // The body is truly optional only in the extern case. This check is handled by the compiler.
+        function_declaration: $=> seq($.typeRef, $.identifier, $.parameters, optional($.blockStatement)),
 
         // Make separate productions for the parser type and the parser type declaration because the latter can have type parameters.
         parserTypeDeclaration: $ => seq(optional($.annotations), $.parser, field('parser_name', $.identifier), optional($.typeParameters), $.parameters),

tree-sitter-p4/test/corpus/declarations.txt

@@ -282,7 +282,6 @@ bool functionb() {
    )
    (identifier)
    (parameters)
-   (statement
    (blockStatement
     (statements
      (statement
@@ -300,7 +299,6 @@ bool functionb() {
   )
  )
 )
-)
 
 =========================
 Function Declaration With Parameters
@@ -340,7 +338,6 @@ bool functionb(bool a, int b) {
      )
     )
    )
-   (statement
    (blockStatement
     (statements
      (statement
@@ -358,7 +355,6 @@ bool functionb(bool a, int b) {
   )
  )
 )
-)
 =========================
 Function Declaration With Parameters And Directions
 =========================
@@ -416,7 +412,6 @@ bool functionb(in bool a, out int b, inout string c) {
      )
     )
    )
-   (statement
    (blockStatement
     (statements
      (statement
@@ -434,4 +429,66 @@ bool functionb(in bool a, out int b, inout string c) {
   )
  )
 )
+=========================
+Extern Function Declaration
+=========================
+extern bool functionb(in bool a, out int b, inout string c);
+---
+(p4program
+ (declaration
+  (extern_declaration
+   (extern)
+   (declaration
+    (function_declaration
+     (typeRef
+      (baseType
+       (bool)
+      )
+     )
+     (identifier)
+     (parameters
+      (parameter_list
+       (parameter_list
+        (parameter_list
+         (parameter
+          (direction
+           (in)
+          )
+          (typeRef
+           (baseType
+           (bool)
+           )
+          )
+          (identifier)
+         )
+        )
+        (parameter
+         (direction
+          (out)
+         )
+         (typeRef
+          (baseType
+           (int)
+          )
+         )
+         (identifier)
+        )
+       )
+       (parameter
+        (direction
+         (inout)
+        )
+        (typeRef
+         (baseType
+          (string)
+         )
+        )
+        (identifier)
+       )
+      )
+     )
+    )
+   )
+  )
+ )
 )

tree-sitter-p4/test/corpus/statements.txt

@@ -43,7 +43,6 @@ int fun() {
    )
    (identifier)
    (parameters)
-   (statement
    (blockStatement
     (statements
      (statement
@@ -60,7 +59,6 @@ int fun() {
   )
  )
 )
-)
 =========================
 Simple If Statement (No Else)
 =========================