compiler, runtime, common: (Initial) Support For extern Declarations

Especially FFI

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

Tests/p4rseTests/Declarations.swift

@@ -176,7 +176,7 @@ import TreeSitterP4
     #RequireErrorResult(
       Error(
         withMessage:
-        "{56, 21}: Failed to parse a statement element: {63, 9}: Failed to parse a statement element: {63, 1}: Cannot assign value with type Boolean to identifier x that is in parameter"
+        "{63, 9}: Failed to parse a statement element: {63, 1}: Cannot assign value with type Boolean to identifier x that is in parameter"
       ),
       Program.Compile(simple_parser_declaration))
   )
@@ -196,7 +196,7 @@ import TreeSitterP4
     #RequireErrorResult(
       Error(
         withMessage:
-        "{113, 27}: Failed to parse a statement element: {120, 15}: Failed to parse a statement element: {120, 7}: Cannot assign to field yesno of x that is in parameter"
+        "{120, 15}: Failed to parse a statement element: {120, 7}: Cannot assign to field yesno of x that is in parameter"
       ),
       Program.Compile(simple_parser_declaration))
   )

Tests/p4rseTests/ExternDeclarations.swift

@@ -0,0 +1,124 @@
+// p4rse, Copyright 2026, Will Hawkins
+//
+// This file is part of p4rse.
+//
+// This file is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+import Common
+import Foundation
+import Macros
+import P4Lang
+import P4Runtime
+import SwiftTreeSitter
+import Testing
+import TreeSitter
+import TreeSitterP4
+
+@testable import P4Compiler
+
+public struct Return5: P4FFI {
+  public func execute(execution: Common.ProgramExecution) -> (
+    Common.ControlFlow, Common.ProgramExecution
+  ) {
+    return (ControlFlow.Return(P4Value(P4IntValue(withValue: 5))), execution)
+  }
+
+  public func parameters() -> ParameterList {
+    return ParameterList()
+  }
+
+  public func type() -> Common.P4Type {
+    return P4Type(
+      FunctionDeclaration(
+        named: Identifier(name: "externally"), ofType: P4Type(P4Int()),
+        withParameters: ParameterList(), withBody: .none?))
+  }
+
+  public init() {}
+}
+
+public struct Return6: P4FFI {
+  public func execute(execution: Common.ProgramExecution) -> (
+    Common.ControlFlow, Common.ProgramExecution
+  ) {
+    return (ControlFlow.Return(P4Value(P4IntValue(withValue: 6))), execution)
+  }
+
+  public func parameters() -> ParameterList {
+    return ParameterList()
+  }
+
+  public func type() -> Common.P4Type {
+    return P4Type(
+      FunctionDeclaration(
+        named: Identifier(name: "externally"), ofType: P4Type(P4Int()),
+        withParameters: ParameterList(), withBody: .none?))
+  }
+
+  public init() {}
+}
+@Test func test_extern_function_declaration() async throws {
+  let simple_parser_declaration = """
+      extern int externally();
+      parser main_parser() {
+        state start {
+          int t = externally();
+          transition select (t == 5) {
+            true: accept;
+            false: reject;
+          };
+        }
+      };
+    """
+
+  let externally = Return5()
+
+  let program = try! #UseOkResult(
+    Program.Compile(
+      simple_parser_declaration, withGlobalInstances: .none, withGlobalTypes: .none,
+      withFFIs: [externally]))
+
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program))
+  let (state_result, _) = try! #UseOkResult(runtime.run())
+
+  #expect(AsInstantiatedParserState(state_result) == P4Lang.accept)
+
+}
+
+@Test func test_extern_function_declaration2() async throws {
+  let simple_parser_declaration = """
+      extern int externally();
+      parser main_parser() {
+        state start {
+          int t = externally();
+          transition select (t == 5) {
+            true: accept;
+            false: reject;
+          };
+        }
+      };
+    """
+
+  let externally = Return6()
+
+  let program = try! #UseOkResult(
+    Program.Compile(
+      simple_parser_declaration, withGlobalInstances: .none, withGlobalTypes: .none,
+      withFFIs: [externally]))
+
+  let runtime = try #UseOkResult(P4Runtime.ParserRuntime.create(program: program))
+  let (state_result, _) = try! #UseOkResult(runtime.run())
+
+  #expect(AsInstantiatedParserState(state_result) == P4Lang.reject)
+}

Tests/p4rseTests/ParserCompilerTests.swift

@@ -98,7 +98,7 @@ import P4Lang
     #RequireErrorResult<(EvaluatableStatement, CompilerContext)>(
       Error(withMessage: "{2, 154}: Did not find assignment statement"),
       ParserAssignmentStatement.Compile( // Note: Calling ParserAssignmentStatement compilation directly.
-        node: result.rootNode!, withContext: CompilerContext(withInstances: VarTypeScopes()))))
+        node: result.rootNode!, withContext: CompilerContext())))
 }
 
 @Test func test_simple_compiler_parser_with_parameters() async throws {