Index: src/Validate/CheckAssertions.cpp
===================================================================
--- src/Validate/CheckAssertions.cpp	(revision a933489bd49da48c88bddbfd58f7fe1c02e90d44)
+++ src/Validate/CheckAssertions.cpp	(revision a933489bd49da48c88bddbfd58f7fe1c02e90d44)
@@ -0,0 +1,96 @@
+//
+// Cforall Version 1.0.0 Copyright (C) 2018 University of Waterloo
+//
+// The contents of this file are covered under the licence agreement in the
+// file "LICENCE" distributed with Cforall.
+//
+// CheckAssertions.cpp --
+//
+// Author           : Andrew Beach
+// Created On       : Thu Sep  5 14:43:00 2024
+// Last Modified By : Andrew Beach
+// Last Modified On : Thu Sep  5 14:43:00 2024
+// Update Count     : 0
+//
+
+#include "CheckAssertions.hpp"
+
+#include "AST/Decl.hpp"
+#include "AST/Pass.hpp"
+#include "AST/Type.hpp"
+#include "Common/SemanticError.hpp"
+#include "GenPoly/GenPoly.hpp"
+
+namespace Validate {
+
+namespace {
+
+/// Check for dynamic (sized polymorphic) variadic assertions.
+struct VariadicAssertionCore final {
+	void checkAssertion( GenPoly::TypeVarMap const & typeVars,
+			ast::FunctionDecl const * assert ) {
+		if ( ast::FixedArgs != assert->type->isVarArgs
+				&& needsAdapter( assert->type, typeVars ) ) {
+			SemanticError( assert,
+				"Cannot assert a function that both has by-value polymorphic "
+				"parameters or return values, and also takes variadic (...) "
+				"parameters. Consider using a va_list parameter instead.\n" );
+		}
+	}
+
+	template<typename T>
+	void checkList(
+			GenPoly::TypeVarMap const & typeVars,
+			SemanticErrorException & errors,
+			std::vector<ast::ptr<T>> const & members ) {
+		for ( const ast::ptr<T> & member : members ) {
+			try {
+				if ( auto func = member.template as<ast::FunctionDecl>() ) {
+					checkAssertion( typeVars, func );
+				}
+			} catch ( SemanticErrorException & error ) {
+				errors.append( error );
+			}
+		}
+	}
+
+	void postvisit( ast::FunctionDecl const * decl ) {
+		GenPoly::TypeVarMap typeVars;
+		SemanticErrorException errors;
+		makeTypeVarMap( decl, typeVars );
+		checkList( typeVars, errors, decl->assertions );
+		if ( !errors.isEmpty() ) { throw errors; }
+	}
+
+	void checkAggr( bool checkMembers,
+			ast::AggregateDecl const * decl ) {
+		SemanticErrorException errors;
+		GenPoly::TypeVarMap typeVars;
+		for ( auto & param : decl->params ) {
+			addToTypeVarMap( param, typeVars );
+			checkList( typeVars, errors, param->assertions );
+		}
+		if ( checkMembers ) checkList( typeVars, errors, decl->members );
+		if ( !errors.isEmpty() ) { throw errors; }
+	}
+
+	void postvisit( ast::StructDecl const * decl ) {
+	checkAggr( false, decl );
+	}
+
+	void postvisit( ast::UnionDecl const * decl ) {
+		checkAggr( false, decl );
+	}
+
+	void postvisit( ast::TraitDecl const * decl ) {
+		checkAggr( true, decl );
+	}
+};
+
+} // namespace
+
+void checkAssertions( ast::TranslationUnit & transUnit ) {
+	ast::Pass<VariadicAssertionCore>::run( transUnit );
+}
+
+} // namespace Validate
Index: src/Validate/CheckAssertions.hpp
===================================================================
--- src/Validate/CheckAssertions.hpp	(revision a933489bd49da48c88bddbfd58f7fe1c02e90d44)
+++ src/Validate/CheckAssertions.hpp	(revision a933489bd49da48c88bddbfd58f7fe1c02e90d44)
@@ -0,0 +1,27 @@
+//
+// Cforall Version 1.0.0 Copyright (C) 2018 University of Waterloo
+//
+// The contents of this file are covered under the licence agreement in the
+// file "LICENCE" distributed with Cforall.
+//
+// CheckAssertions.hpp -- Check for invalid assertions.
+//
+// Author           : Andrew Beach
+// Created On       : Thu Sep  5 14:41:00 2024
+// Last Modified By : Andrew Beach
+// Last Modified On : Thu Sep  5 14:41:00 2024
+// Update Count     : 0
+//
+
+#pragma once
+
+namespace ast {
+	class TranslationUnit;
+}
+
+namespace Validate {
+
+/// Checks for problems in an assertion list.
+void checkAssertions( ast::TranslationUnit & transUnit );
+
+}
Index: src/Validate/module.mk
===================================================================
--- src/Validate/module.mk	(revision 63d5b9c813497aa370ec41bc6b32ec92e82c0831)
+++ src/Validate/module.mk	(revision a933489bd49da48c88bddbfd58f7fe1c02e90d44)
@@ -21,4 +21,6 @@
 	Validate/Autogen.cpp \
 	Validate/Autogen.hpp \
+	Validate/CheckAssertions.cpp \
+	Validate/CheckAssertions.hpp \
 	Validate/CompoundLiteral.cpp \
 	Validate/CompoundLiteral.hpp \