compiler, common, testing: Support For Checking For Invalid Statements

Add support functions to check whether a (block of) statement(s) contains
any statements that should not appear in that block (e.g., switch in
an action).

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

Sources/P4Compiler/Common.swift

@@ -351,3 +351,25 @@ extension Argument: Compilable {
     }
   }
 }
+
+func ContainsInvalidStatements(
+  statement: EvaluatableStatement, invalids: [EvaluatableStatement.Type]
+) -> Bool {
+  for es in invalids {
+    if type(of: statement) == es {
+      return true
+    }
+  }
+  return false
+}
+
+func ContainsInvalidStatements(block: BlockStatement, invalids: [EvaluatableStatement.Type]) -> Bool {
+  return block.statements.contains() { statement in
+    for es in invalids {
+      if type(of: statement) == es {
+        return true
+      }
+    }
+    return false
+  }
+}

Tests/p4rseTests/SupportTests/InvalidStatements.swift

@@ -0,0 +1,58 @@
+// 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
+
+@Test func test_invalid_statements() async throws {
+
+  let ret = ReturnStatement(P4Value(P4IntValue(withValue: 5)))
+  let block = BlockStatement([ret])
+
+  #expect(ContainsInvalidStatements(block: block, invalids: [ReturnStatement.self]))
+}
+
+@Test func test_no_invalid_statements() async throws {
+
+  let exprs = ExpressionStatement(P4Value(P4IntValue(withValue: 5)))
+  let block = BlockStatement([exprs])
+
+  #expect(!ContainsInvalidStatements(block: block, invalids: [ReturnStatement.self]))
+}
+
+@Test func test_is_invalid_statement() async throws {
+
+  let ret = ReturnStatement(P4Value(P4IntValue(withValue: 5)))
+
+  #expect(ContainsInvalidStatements(statement: ret, invalids: [ReturnStatement.self]))
+}
+
+@Test func test_no_is_invalid_statement() async throws {
+
+  let exprs = ExpressionStatement(P4Value(P4IntValue(withValue: 5)))
+
+  #expect(!ContainsInvalidStatements(statement: exprs, invalids: [ReturnStatement.self]))
+}