Reduce capabilities of `Diagnostic`.

Currently many diagnostic modifier methods are available on both
`Diagnostic` and `DiagnosticBuilder`. This commit removes most of them
from `Diagnostic`. To minimize the diff size, it keeps them within
`diagnostic.rs` but changes the surrounding `impl Diagnostic` block to
`impl DiagnosticBuilder`. (I intend to move things around later, to give
a more sensible code layout.)

`Diagnostic` keeps a few methods that it still needs, like `sub`,
`arg`, and `replace_args`.

The `forward!` macro, which defined two additional methods per call
(e.g. `note` and `with_note`), is replaced by the `with_fn!` macro,
which defines one additional method per call (e.g. `with_note`). It's
now also only used when necessary -- not all modifier methods currently
need a `with_*` form. (New ones can be easily added as necessary.)

All this also requires changing `trait AddToDiagnostic` so its methods
take `DiagnosticBuilder` instead of `Diagnostic`, which leads to many
mechanical changes. `SubdiagnosticMessageOp` gains a type parameter `G`.

There are three subdiagnostics -- `DelayedAtWithoutNewline`,
`DelayedAtWithNewline`, and `InvalidFlushedDelayedDiagnosticLevel` --
that are created within the diagnostics machinery and appended to
external diagnostics. These are handled at the `Diagnostic` level, which
means it's now hard to construct them via `derive(Diagnostic)`, so
instead we construct them by hand. This has no effect on what they look
like when printed.

There are lots of new `allow` markers for `untranslatable_diagnostics`
and `diagnostics_outside_of_impl`. This is because
`#[rustc_lint_diagnostics]` annotations were present on the `Diagnostic`
modifier methods, but missing from the `DiagnosticBuilder` modifier
methods. They're now present.

1 files changed, 7 insertions, 0 deletions

diff --git a/compiler/rustc_const_eval/src/transform/check_consts/ops.rs b/compiler/rustc_const_eval/src/transform/check_consts/ops.rs
index 25ddd5e85f9..5b4bbf8510b 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/ops.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/ops.rs
@@ -93,6 +93,9 @@ pub struct FnCallNonConst<'tcx> {
 }
 
 impl<'tcx> NonConstOp<'tcx> for FnCallNonConst<'tcx> {
+    // FIXME: make this translatable
+    #[allow(rustc::diagnostic_outside_of_impl)]
+    #[allow(rustc::untranslatable_diagnostic)]
     fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, _: Span) -> DiagnosticBuilder<'tcx> {
         let FnCallNonConst { caller, callee, args, span, call_source, feature } = *self;
         let ConstCx { tcx, param_env, .. } = *ccx;
@@ -321,6 +324,8 @@ impl<'tcx> NonConstOp<'tcx> for FnCallUnstable {
             .dcx()
             .create_err(errors::UnstableConstFn { span, def_path: ccx.tcx.def_path_str(def_id) });
 
+        // FIXME: make this translatable
+        #[allow(rustc::untranslatable_diagnostic)]
         if ccx.is_const_stable_const_fn() {
             err.help("const-stable functions can only call other const-stable functions");
         } else if ccx.tcx.sess.is_nightly_build() {
@@ -591,6 +596,8 @@ impl<'tcx> NonConstOp<'tcx> for StaticAccess {
             span,
             format!("referencing statics in {}s is unstable", ccx.const_kind(),),
         );
+        // FIXME: make this translatable
+        #[allow(rustc::untranslatable_diagnostic)]
         err
             .note("`static` and `const` variables can refer to other `const` variables. A `const` variable, however, cannot refer to a `static` variable.")
             .help("to fix this, the value can be extracted to a `const` and then used.");