lint: add bad opt access internal lint

Some command-line options accessible through `sess.opts` are best
accessed through wrapper functions on `Session`, `TyCtxt` or otherwise,
rather than through field access on the option struct in the `Session`.

Adds a new lint which triggers on those options that should be accessed
through a wrapper function so that this is prohibited. Options are
annotated with a new attribute `rustc_lint_opt_deny_field_access` which
can specify the error message (i.e. "use this other function instead")
to be emitted.

A simpler alternative would be to simply rename the options in the
option type so that it is clear they should not be used, however this
doesn't prevent uses, just discourages them. Another alternative would
be to make the option fields private, and adding accessor functions on
the option types, however the wrapper functions sometimes rely on
additional state from `Session` or `TyCtxt` which wouldn't be available
in an function on the option type, so the accessor would simply make the
field available and its use would be discouraged too.

Signed-off-by: David Wood <david.wood@huawei.com>

Author: davidtwco

compiler/rustc_driver/src/lib.rs

@@ -123,8 +123,7 @@ impl Callbacks for TimePassesCallbacks {
     fn config(&mut self, config: &mut interface::Config) {
         // If a --prints=... option has been given, we don't print the "total"
         // time because it will mess up the --prints output. See #64339.
-        self.time_passes = config.opts.prints.is_empty()
-            && (config.opts.unstable_opts.time_passes || config.opts.unstable_opts.time);
+        self.time_passes = config.opts.prints.is_empty() && config.opts.time_passes();
         config.opts.trimmed_def_paths = TrimmedDefPaths::GoodPath;
     }
 }

compiler/rustc_error_messages/locales/en-US/passes.ftl

@@ -256,3 +256,9 @@ passes-unused-duplicate = unused attribute
 passes-unused-multiple = multiple `{$name}` attributes
     .suggestion = remove this attribute
     .note = attribute also specified here
+
+passes-rustc-lint-opt-ty = `#[rustc_lint_opt_ty]` should be applied to a struct
+    .label = not a struct
+
+passes-rustc-lint-opt-deny-field-access = `#[rustc_lint_opt_deny_field_access]` should be applied to a field
+    .label = not a field

compiler/rustc_feature/src/builtin_attrs.rs

@@ -619,6 +619,12 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // Used by the `rustc::untranslatable_diagnostic` and `rustc::diagnostic_outside_of_impl` lints
     // to assist in changes to diagnostic APIs.
     rustc_attr!(rustc_lint_diagnostics, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE),
+    // Used by the `rustc::bad_opt_access` lint to identify `DebuggingOptions` and `CodegenOptions`
+    // types (as well as any others in future).
+    rustc_attr!(rustc_lint_opt_ty, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE),
+    // Used by the `rustc::bad_opt_access` lint on fields
+    // types (as well as any others in future).
+    rustc_attr!(rustc_lint_opt_deny_field_access, Normal, template!(List: "message"), WarnFollowing, INTERNAL_UNSTABLE),
 
     // ==========================================================================
     // Internal attributes, Const related:

compiler/rustc_interface/src/interface.rs

@@ -329,6 +329,8 @@ pub fn create_compiler_and_run<R>(config: Config, f: impl FnOnce(&Compiler) -> R
     })
 }
 
+// JUSTIFICATION: before session exists, only config
+#[cfg_attr(not(bootstrap), allow(rustc::bad_opt_access))]
 pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Send) -> R {
     tracing::trace!("run_compiler");
     util::run_in_thread_pool_with_globals(

compiler/rustc_interface/src/tests.rs

@@ -1,3 +1,4 @@
+#![cfg_attr(not(bootstrap), allow(rustc::bad_opt_access))]
 use crate::interface::parse_cfgspecs;
 
 use rustc_data_structures::fx::FxHashSet;

compiler/rustc_interface/src/util.rs

@@ -559,6 +559,8 @@ pub fn collect_crate_types(session: &Session, attrs: &[ast::Attribute]) -> Vec<C
     // Only check command line flags if present. If no types are specified by
     // command line, then reuse the empty `base` Vec to hold the types that
     // will be found in crate attributes.
+    // JUSTIFICATION: before wrapper fn is available
+    #[cfg_attr(not(bootstrap), allow(rustc::bad_opt_access))]
     let mut base = session.opts.crate_types.clone();
     if base.is_empty() {
         base.extend(attr_types);

compiler/rustc_lint/src/internal.rs

@@ -432,3 +432,38 @@ impl LateLintPass<'_> for Diagnostics {
         }
     }
 }
+
+declare_tool_lint! {
+    pub rustc::BAD_OPT_ACCESS,
+    Deny,
+    "prevent using options by field access when there is a wrapper function",
+    report_in_external_macro: true
+}
+
+declare_lint_pass!(BadOptAccess => [ BAD_OPT_ACCESS ]);
+
+impl LateLintPass<'_> for BadOptAccess {
+    fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
+        let ExprKind::Field(base, target) = expr.kind else { return };
+        let Some(adt_def) = cx.typeck_results().expr_ty(base).ty_adt_def() else { return };
+        // Skip types without `#[rustc_lint_opt_ty]` - only so that the rest of the lint can be
+        // avoided.
+        if !cx.tcx.has_attr(adt_def.did(), sym::rustc_lint_opt_ty) {
+            return;
+        }
+
+        for field in adt_def.all_fields() {
+            if field.name == target.name &&
+                let Some(attr) = cx.tcx.get_attr(field.did, sym::rustc_lint_opt_deny_field_access) &&
+                let Some(items) = attr.meta_item_list()  &&
+                let Some(item) = items.first()  &&
+                let Some(literal) = item.literal()  &&
+                let ast::LitKind::Str(val, _) = literal.kind
+            {
+                cx.struct_span_lint(BAD_OPT_ACCESS, expr.span, |lint| {
+                    lint.build(val.as_str()).emit(); }
+                );
+            }
+        }
+    }
+}

compiler/rustc_lint/src/lib.rs

@@ -509,6 +509,8 @@ fn register_internals(store: &mut LintStore) {
     store.register_late_pass(|| Box::new(TyTyKind));
     store.register_lints(&Diagnostics::get_lints());
     store.register_late_pass(|| Box::new(Diagnostics));
+    store.register_lints(&BadOptAccess::get_lints());
+    store.register_late_pass(|| Box::new(BadOptAccess));
     store.register_lints(&PassByValue::get_lints());
     store.register_late_pass(|| Box::new(PassByValue));
     // FIXME(davidtwco): deliberately do not include `UNTRANSLATABLE_DIAGNOSTIC` and
@@ -527,6 +529,7 @@ fn register_internals(store: &mut LintStore) {
             LintId::of(LINT_PASS_IMPL_WITHOUT_MACRO),
             LintId::of(USAGE_OF_QUALIFIED_TY),
             LintId::of(EXISTING_DOC_KEYWORD),
+            LintId::of(BAD_OPT_ACCESS),
         ],
     );
 }

compiler/rustc_mir_transform/src/lower_slice_len.rs

@@ -11,7 +11,7 @@ pub struct LowerSliceLenCalls;
 
 impl<'tcx> MirPass<'tcx> for LowerSliceLenCalls {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
-        sess.opts.mir_opt_level() > 0
+        sess.mir_opt_level() > 0
     }
 
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {

compiler/rustc_mir_transform/src/reveal_all.rs

@@ -9,7 +9,7 @@ pub struct RevealAll;
 
 impl<'tcx> MirPass<'tcx> for RevealAll {
     fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
-        sess.opts.mir_opt_level() >= 3 || super::inline::Inline.is_enabled(sess)
+        sess.mir_opt_level() >= 3 || super::inline::Inline.is_enabled(sess)
     }
 
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {