improve error messages

compiler/checker/checker.odin

@@ -3905,17 +3905,83 @@ runtime_write_declaration_matches :: proc(checker: ^Checker, function: ast.Funct
 	       type_from_syntax(checker, function.result, function.pkg, function.file) == types.C_LONG
 }
 
+signature_type_diagnostic :: proc(
+	checker: ^Checker,
+	function: ast.Function,
+	value: types.Type,
+	depth := 0,
+) -> source.Diagnostic_Id {
+	if depth > 64 || is_type_metatype_syntax(checker, value) {
+		return source.INVALID_DIAGNOSTIC
+	}
+	item, ok := types.node(&checker.module.types, value)
+	if !ok {
+		return source.INVALID_DIAGNOSTIC
+	}
+	if item.kind == .Named && !item.declared && item.qualifier == 0 {
+		name := symbol.Id(item.name)
+		if param, found := comptime_param_for_name(function, name);
+		   found && is_comptime_type_param(checker, param) {
+			return source.INVALID_DIAGNOSTIC
+		}
+		span := function.span
+		for type_use in checker.ast_module.type_uses {
+			if type_use.file == function.file && type_use.type == value &&
+			   type_use.span.start >= function.span.start && type_use.span.end <= function.span.end {
+				span = type_use.span
+				break
+			}
+		}
+		diagnostic := source.addf(
+			checker.diagnostics,
+			span,
+			"unknown symbol '%s'",
+			symbol_text(checker, name),
+		)
+		source.set_primary_label(checker.diagnostics, diagnostic, "unknown symbol")
+		return diagnostic
+	}
+	if diagnostic := signature_type_diagnostic(
+		checker, function, item.child, depth+1,
+	); diagnostic != source.INVALID_DIAGNOSTIC {
+		return diagnostic
+	}
+	if diagnostic := signature_type_diagnostic(
+		checker, function, item.extra, depth+1,
+	); diagnostic != source.INVALID_DIAGNOSTIC {
+		return diagnostic
+	}
+	if item.kind == .Function {
+		for param in types.params_for(&checker.module.types, value) {
+			if diagnostic := signature_type_diagnostic(
+				checker, function, param.type, depth+1,
+			); diagnostic != source.INVALID_DIAGNOSTIC {
+				return diagnostic
+			}
+		}
+	}
+	return source.INVALID_DIAGNOSTIC
+}
+
 validate_declarations :: proc(checker: ^Checker) {
 	for function, function_id in checker.ast_module.functions {
 		if len(function.unsupported_reason) > 0 {
 			continue
 		}
 		has_comptime := function_has_comptime_params(function)
-		signature_poisoned := function.diagnostic != source.INVALID_DIAGNOSTIC
+		signature_poisoned := checker.template_diagnostics[function_id] != source.INVALID_DIAGNOSTIC
 		locals: [dynamic]symbol.Id
 		locals.allocator = checker.allocator
 		comptime_prefix := 0
 		for param in function.params {
+			if !signature_poisoned {
+				if diagnostic := signature_type_diagnostic(
+					checker, function, param.type,
+				); diagnostic != source.INVALID_DIAGNOSTIC {
+					checker.template_diagnostics[function_id] = diagnostic
+					signature_poisoned = true
+				}
+			}
 			dependent := param.comptime_value && type_pattern_mentions_comptime(
 				checker, function, comptime_prefix, param.type,
 			)
@@ -3994,6 +4060,18 @@ validate_declarations :: proc(checker: ^Checker) {
 				)
 			}
 		}
+		if !signature_poisoned {
+			signature_types := [2]types.Type{function.result, function.error}
+			for value in signature_types {
+				if diagnostic := signature_type_diagnostic(
+					checker, function, value,
+				); diagnostic != source.INVALID_DIAGNOSTIC {
+					checker.template_diagnostics[function_id] = diagnostic
+					signature_poisoned = true
+					break
+				}
+			}
+		}
 		if !has_comptime && !signature_poisoned {
 			result_type := type_from_syntax(checker, function.result, function.pkg, function.file)
 			if function.c_abi && types.is_noreturn(result_type) {