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>

3 files changed, 5 insertions, 0 deletions

diff --git a/compiler/rustc_interface/src/interface.rs b/compiler/rustc_interface/src/interface.rs
index 6c7ddb4531e..94f81b66077 100644
--- a/compiler/rustc_interface/src/interface.rs
+++ b/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(
diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index 0a0eb99cd92..21d9eaccf67 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/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;
diff --git a/compiler/rustc_interface/src/util.rs b/compiler/rustc_interface/src/util.rs
index 97856ecf22c..4c64e679b95 100644
--- a/compiler/rustc_interface/src/util.rs
+++ b/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);