stashing: tweak ExpnData based on eddyb's feedback.

src/librustc/lint.rs

@@ -342,7 +342,8 @@ pub fn in_external_macro(sess: &Session, span: Span) -> bool {
     let expn_data = span.ctxt().outer_expn_data();
     match expn_data.kind {
         ExpnKind::Root | ExpnKind::Desugaring(DesugaringKind::ForLoop) => false,
-        ExpnKind::AstPass(_) | ExpnKind::Desugaring(_) => true, // well, it's "external"
+        // well, it's "external"
+        ExpnKind::AstPass(_) | ExpnKind::Desugaring(_) | ExpnKind::ParserRecovery => true,
         ExpnKind::Macro(MacroKind::Bang, _) => {
             if expn_data.def_site.is_dummy() {
                 // Dummy span for the `def_site` means it's an external macro.

src/librustc_errors/diagnostic_builder.rs

@@ -2,7 +2,7 @@ use crate::{Applicability, Handler, Level, StashKey};
 use crate::{Diagnostic, DiagnosticId, DiagnosticStyledString};
 
 use log::debug;
-use rustc_span::{MultiSpan, Span};
+use rustc_span::{ExpnData, ExpnKind, MultiSpan, Span};
 use std::fmt::{self, Debug};
 use std::ops::{Deref, DerefMut};
 use std::thread::panicking;
@@ -133,7 +133,8 @@ impl<'a> DiagnosticBuilder<'a> {
             // suite! { len; is_empty; }
             // ```
             // ...would result in overwriting due to using the same `def_site` span for `A`.
-            let span = span.fresh_expansion(span.ctxt().outer_expn_data());
+            let data = ExpnData::default(ExpnKind::ParserRecovery, span, span.edition());
+            let span = span.fresh_expansion(data);
             handler.stash_diagnostic(span, key, diag);
             span
         })

src/librustc_errors/emitter.rs

@@ -293,7 +293,9 @@ pub trait Emitter {
 
                         // Skip past non-macro entries, just in case there
                         // are some which do actually involve macros.
-                        ExpnKind::Desugaring(..) | ExpnKind::AstPass(..) => None,
+                        ExpnKind::Desugaring(..)
+                        | ExpnKind::AstPass(..)
+                        | ExpnKind::ParserRecovery => None,
 
                         ExpnKind::Macro(macro_kind, _) => Some(macro_kind),
                     }

src/librustc_save_analysis/lib.rs

@@ -789,7 +789,10 @@ impl<'l, 'tcx> SaveContext<'l, 'tcx> {
 
             // These are not macros.
             // FIXME(eddyb) maybe there is a way to handle them usefully?
-            ExpnKind::Root | ExpnKind::AstPass(_) | ExpnKind::Desugaring(_) => return None,
+            ExpnKind::Root
+            | ExpnKind::AstPass(_)
+            | ExpnKind::Desugaring(_)
+            | ExpnKind::ParserRecovery => return None,
         };
 
         // If the callee is an imported macro from an external crate, need to get

src/librustc_span/hygiene.rs

@@ -729,6 +729,8 @@ pub enum ExpnKind {
     AstPass(AstPass),
     /// Desugaring done by the compiler during HIR lowering.
     Desugaring(DesugaringKind),
+    /// AST fragements produced by parser recovery.
+    ParserRecovery,
 }
 
 impl ExpnKind {
@@ -742,6 +744,7 @@ impl ExpnKind {
             },
             ExpnKind::AstPass(kind) => kind.descr().to_string(),
             ExpnKind::Desugaring(kind) => format!("desugaring of {}", kind.descr()),
+            ExpnKind::ParserRecovery => "parser recovery".to_string(),
         }
     }
 }