Improve testing and error messages for malformed attributes

compiler/rustc_attr_parsing/src/attributes/must_use.rs

@@ -21,7 +21,16 @@ impl<S: Stage> SingleAttributeParser<S> for MustUseParser {
             span: cx.attr_span,
             reason: match args {
                 ArgParser::NoArgs => None,
-                ArgParser::NameValue(name_value) => name_value.value_as_str(),
+                ArgParser::NameValue(name_value) => {
+                    let Some(value_str) = name_value.value_as_str() else {
+                        cx.expected_string_literal(
+                            name_value.value_span,
+                            Some(&name_value.value_as_lit()),
+                        );
+                        return None;
+                    };
+                    Some(value_str)
+                }
                 ArgParser::List(_) => {
                     let suggestions =
                         <Self as SingleAttributeParser<S>>::TEMPLATE.suggestions(false, "must_use");

compiler/rustc_attr_parsing/src/session_diagnostics.rs

@@ -566,10 +566,7 @@ impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for AttributeParseError {
                 diag.code(E0565);
             }
             AttributeParseErrorReason::ExpectedNameValue(None) => {
-                diag.span_label(
-                    self.span,
-                    format!("expected this to be of the form `{name} = \"...\"`"),
-                );
+                // The suggestion we add below this match already contains enough information
             }
             AttributeParseErrorReason::ExpectedNameValue(Some(name)) => {
                 diag.span_label(

compiler/rustc_parse/src/validate_attr.rs

@@ -303,6 +303,8 @@ fn emit_malformed_attribute(
             | sym::must_use
             | sym::track_caller
             | sym::link_name
+            | sym::export_name
+            | sym::rustc_macro_transparency
     ) {
         return;
     }

tests/ui/attributes/malformed-attrs.rs

@@ -0,0 +1,221 @@
+// This file contains a bunch of malformed attributes.
+// We enable a bunch of features to not get feature-gate errs in this test.
+#![feature(rustc_attrs)]
+#![feature(rustc_allow_const_fn_unstable)]
+#![feature(allow_internal_unstable)]
+#![feature(fn_align)]
+#![feature(optimize_attribute)]
+#![feature(dropck_eyepatch)]
+#![feature(export_stable)]
+#![allow(incomplete_features)]
+#![feature(min_generic_const_args)]
+#![feature(ffi_const, ffi_pure)]
+#![feature(coverage_attribute)]
+#![feature(no_sanitize)]
+#![feature(marker_trait_attr)]
+#![feature(thread_local)]
+#![feature(must_not_suspend)]
+#![feature(coroutines)]
+#![feature(linkage)]
+#![feature(cfi_encoding, extern_types)]
+#![feature(patchable_function_entry)]
+#![feature(omit_gdb_pretty_printer_section)]
+#![feature(fundamental)]
+
+
+#![omit_gdb_pretty_printer_section = 1]
+//~^ ERROR malformed `omit_gdb_pretty_printer_section` attribute input
+
+#![windows_subsystem]
+//~^ ERROR malformed
+
+#[unsafe(export_name)]
+//~^ ERROR malformed
+#[rustc_allow_const_fn_unstable]
+//~^ ERROR `rustc_allow_const_fn_unstable` expects a list of feature names
+#[allow_internal_unstable]
+//~^ ERROR `allow_internal_unstable` expects a list of feature names
+#[rustc_confusables]
+//~^ ERROR malformed
+#[deprecated = 5]
+//~^ ERROR malformed
+#[doc]
+//~^ ERROR valid forms for the attribute are
+//~| WARN this was previously accepted by the compiler
+#[rustc_macro_transparency]
+//~^ ERROR malformed
+#[repr]
+//~^ ERROR malformed
+#[rustc_as_ptr = 5]
+//~^ ERROR malformed
+#[inline = 5]
+//~^ ERROR valid forms for the attribute are
+//~| WARN this was previously accepted by the compiler
+#[align]
+//~^ ERROR malformed
+#[optimize]
+//~^ ERROR malformed
+#[cold = 1]
+//~^ ERROR malformed
+#[must_use()]
+//~^ ERROR valid forms for the attribute are
+#[no_mangle = 1]
+//~^ ERROR malformed
+#[unsafe(naked())]
+//~^ ERROR malformed
+#[track_caller()]
+//~^ ERROR malformed
+#[export_name()]
+//~^ ERROR malformed
+#[used()]
+//~^ ERROR malformed
+#[crate_name]
+//~^ ERROR malformed
+#[doc]
+//~^ ERROR valid forms for the attribute are
+//~| WARN this was previously accepted by the compiler
+#[target_feature]
+//~^ ERROR malformed
+#[export_stable = 1]
+//~^ ERROR malformed
+#[link]
+//~^ ERROR attribute must be of the form
+//~| WARN this was previously accepted by the compiler
+#[link_name]
+//~^ ERROR malformed
+#[link_section]
+//~^ ERROR malformed
+#[coverage]
+//~^ ERROR malformed `coverage` attribute input
+#[no_sanitize]
+//~^ ERROR malformed
+#[ignore()]
+//~^ ERROR valid forms for the attribute are
+//~| WARN this was previously accepted by the compiler
+#[no_implicit_prelude = 23]
+//~^ ERROR malformed
+#[proc_macro = 18]
+//~^ ERROR malformed
+//~| ERROR the `#[proc_macro]` attribute is only usable with crates of the `proc-macro` crate type
+#[cfg]
+//~^ ERROR is not followed by parentheses
+#[cfg_attr]
+//~^ ERROR malformed
+#[instruction_set]
+//~^ ERROR malformed
+#[patchable_function_entry]
+//~^ ERROR malformed
+fn test() {
+    #[coroutine = 63] || {}
+    //~^ ERROR malformed `coroutine` attribute input
+    //~| ERROR mismatched types [E0308]
+}
+
+#[proc_macro_attribute = 19]
+//~^ ERROR malformed
+//~| ERROR the `#[proc_macro_attribute]` attribute is only usable with crates of the `proc-macro` crate type
+#[must_use = 1]
+//~^ ERROR malformed
+fn test2() { }
+
+#[proc_macro_derive]
+//~^ ERROR malformed `proc_macro_derive` attribute
+//~| ERROR the `#[proc_macro_derive]` attribute is only usable with crates of the `proc-macro` crate type
+pub fn test3() {}
+
+#[rustc_layout_scalar_valid_range_start]
+//~^ ERROR malformed
+#[rustc_layout_scalar_valid_range_end]
+//~^ ERROR malformed
+#[must_not_suspend()]
+//~^ ERROR malformed
+#[cfi_encoding]
+//~^ ERROR malformed
+struct Test;
+
+#[diagnostic::on_unimplemented]
+//~^ WARN missing options for `on_unimplemented` attribute
+#[diagnostic::on_unimplemented = 1]
+//~^ WARN malformed
+trait Hey {
+    #[type_const = 1]
+    //~^ ERROR malformed
+    const HEY: usize = 5;
+}
+
+struct Empty;
+#[diagnostic::do_not_recommend()]
+//~^ WARN does not expect any arguments
+impl Hey for Empty {
+
+}
+
+#[marker = 3]
+//~^ ERROR malformed
+#[fundamental()]
+//~^ ERROR malformed
+trait EmptyTrait {
+
+}
+
+
+extern "C" {
+    #[unsafe(ffi_pure = 1)]
+    //~^ ERROR malformed
+    #[link_ordinal]
+    //~^ ERROR malformed
+    pub fn baz();
+
+    #[unsafe(ffi_const = 1)]
+    //~^ ERROR malformed
+    #[linkage]
+    //~^ ERROR malformed
+    pub fn bar();
+}
+
+#[allow]
+//~^ ERROR malformed
+#[expect]
+//~^ ERROR malformed
+#[warn]
+//~^ ERROR malformed
+#[deny]
+//~^ ERROR malformed
+#[forbid]
+//~^ ERROR malformed
+#[debugger_visualizer]
+//~^ ERROR invalid argument
+//~| ERROR malformed `debugger_visualizer` attribute input
+#[automatically_derived = 18]
+//~^ ERROR malformed
+mod yooo {
+
+}
+
+#[non_exhaustive = 1]
+//~^ ERROR malformed
+enum Slenum {
+
+}
+
+#[thread_local()]
+//~^ ERROR malformed
+static mut TLS: u8 = 42;
+
+#[no_link()]
+//~^ ERROR malformed
+#[macro_use = 1]
+//~^ ERROR malformed
+extern crate wloop;
+//~^ ERROR can't find crate for `wloop` [E0463]
+
+#[macro_export = 18]
+//~^ ERROR malformed `macro_export` attribute input
+#[allow_internal_unsafe = 1]
+//~^ ERROR malformed
+//~| ERROR allow_internal_unsafe side-steps the unsafe_code lint
+macro_rules! slump {
+    () => {}
+}
+
+fn main() {}