"Fix" an overflow in byte position math

compiler/rustc_errors/src/lib.rs

@@ -13,9 +13,11 @@
 #[macro_use]
 extern crate rustc_macros;
 
+#[macro_use]
+extern crate tracing;
+
 pub use emitter::ColorConfig;
 
-use tracing::debug;
 use Level::*;
 
 use emitter::{is_case_difference, Emitter, EmitterWriter};

compiler/rustc_parse/src/lib.rs

@@ -6,6 +6,9 @@
 #![feature(box_patterns)]
 #![recursion_limit = "256"]
 
+#[macro_use]
+extern crate tracing;
+
 use rustc_ast as ast;
 use rustc_ast::token::{self, Nonterminal, Token, TokenKind};
 use rustc_ast::tokenstream::{self, AttributesData, CanSynthesizeMissingTokens, LazyTokenStream};

compiler/rustc_parse/src/parser/expr.rs

@@ -1084,6 +1084,7 @@ impl<'a> Parser<'a> {
 
     /// If we encounter a parser state that looks like the user has written a `struct` literal with
     /// parentheses instead of braces, recover the parser state and provide suggestions.
+    #[instrument(skip(self, seq, snapshot), level = "trace")]
     fn maybe_recover_struct_lit_bad_delims(
         &mut self,
         lo: Span,

compiler/rustc_span/src/lib.rs

@@ -25,6 +25,9 @@
 #[macro_use]
 extern crate rustc_macros;
 
+#[macro_use]
+extern crate tracing;
+
 use rustc_data_structures::AtomicRef;
 use rustc_macros::HashStable_Generic;
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
@@ -782,13 +785,30 @@ impl Span {
     ///     ^^^^^^^^^^^^^^^^^
     /// ```
     pub fn until(self, end: Span) -> Span {
-        let span = self.data();
-        let end = end.data();
+        // Most of this function's body is copied from `to`.
+        // We can't just do `self.to(end.shrink_to_lo())`,
+        // because to also does some magic where it uses min/max so
+        // it can handle overlapping spans. Some advanced mis-use of
+        // `until` with different ctxts makes this visible.
+        let span_data = self.data();
+        let end_data = end.data();
+        // FIXME(jseyfried): `self.ctxt` should always equal `end.ctxt` here (cf. issue #23480).
+        // Return the macro span on its own to avoid weird diagnostic output. It is preferable to
+        // have an incomplete span than a completely nonsensical one.
+        if span_data.ctxt != end_data.ctxt {
+            if span_data.ctxt == SyntaxContext::root() {
+                return end;
+            } else if end_data.ctxt == SyntaxContext::root() {
+                return self;
+            }
+            // Both spans fall within a macro.
+            // FIXME(estebank): check if it is the *same* macro.
+        }
         Span::new(
-            span.lo,
-            end.lo,
-            if end.ctxt == SyntaxContext::root() { end.ctxt } else { span.ctxt },
-            if span.parent == end.parent { span.parent } else { None },
+            span_data.lo,
+            end_data.lo,
+            if end_data.ctxt == SyntaxContext::root() { end_data.ctxt } else { span_data.ctxt },
+            if span_data.parent == end_data.parent { span_data.parent } else { None },
         )
     }
 

compiler/rustc_span/src/source_map.rs

@@ -474,11 +474,12 @@ impl SourceMap {
         f.lookup_line(sp.lo()) != f.lookup_line(sp.hi())
     }
 
+    #[instrument(skip(self), level = "trace")]
     pub fn is_valid_span(&self, sp: Span) -> Result<(Loc, Loc), SpanLinesError> {
         let lo = self.lookup_char_pos(sp.lo());
-        debug!("span_to_lines: lo={:?}", lo);
+        trace!(?lo);
         let hi = self.lookup_char_pos(sp.hi());
-        debug!("span_to_lines: hi={:?}", hi);
+        trace!(?hi);
         if lo.file.start_pos != hi.file.start_pos {
             return Err(SpanLinesError::DistinctSources(DistinctSources {
                 begin: (lo.file.name.clone(), lo.file.start_pos),

src/test/ui/parser/issue-44406.stderr

@@ -26,7 +26,7 @@ LL |         bar {  }
 help: if `bar` is a function, use the arguments directly
    |
 LL -         bar(baz: $rest)
-LL +         bar(true);
+LL +         bar(: $rest)
    | 
 
 error: aborting due to 2 previous errors