analyze: discard annotations on DUMMY_SP

c2rust-analyze/src/analyze.rs

@@ -50,7 +50,7 @@ use rustc_middle::ty::Ty;
 use rustc_middle::ty::TyCtxt;
 use rustc_middle::ty::TyKind;
 use rustc_middle::ty::WithOptConstParam;
-use rustc_span::{Span, Symbol, DUMMY_SP};
+use rustc_span::{Span, Symbol};
 use std::collections::HashMap;
 use std::collections::HashSet;
 use std::env;
@@ -1544,7 +1544,13 @@ fn run(tcx: TyCtxt) {
         }
 
         // Emit annotations for fields
-        let span = tcx.def_ident_span(did).unwrap_or(DUMMY_SP);
+        let span = match tcx.def_ident_span(did) {
+            Some(x) => x,
+            None => {
+                warn!("field {:?} has no def_ident_span to annotate", did);
+                continue;
+            }
+        };
         let mut ptrs = Vec::new();
         let ty_str = context::print_ty_with_pointer_labels(field_lty, |ptr| {
             if ptr.is_none() {

c2rust-analyze/src/annotate.rs

@@ -1,3 +1,4 @@
+use log::warn;
 use rustc_middle::ty::TyCtxt;
 use rustc_span::{FileName, Span};
 use std::collections::HashMap;
@@ -22,6 +23,16 @@ impl<'tcx> AnnotationBuffer<'tcx> {
     }
 
     pub fn emit(&mut self, span: Span, msg: impl Display) {
+        if span.is_dummy() {
+            // `DUMMY_SP` covers the range `BytePos(0) .. BytePos(0)`.  Whichever file happens to
+            // be added to the `SourceMap` first will be assigned a range starting at `BytePos(0)`,
+            // so the `SourceFile` lookup below would attach the annotation to that file.  Rather
+            // than letting the annotation be attached to an arbitrary file, we warn and discard
+            // it.
+            warn!("discarding annotation on DUMMY_SP: {}", msg);
+            return;
+        }
+
         let sm = self.tcx.sess.source_map();
 
         let span = span.source_callsite();