Identify when a stmt could have been parsed as an expr

There are some expressions that can be parsed as a statement without
a trailing semicolon depending on the context, which can lead to
confusing errors due to the same looking code being accepted in some
places and not others. Identify these cases and suggest enclosing in
parenthesis making the parse non-ambiguous without changing the
accepted grammar.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/libsyntax/parse/mod.rs b/src/libsyntax/parse/mod.rs
index 1abc7832ffa..94bbd5ba2f7 100644
--- a/src/libsyntax/parse/mod.rs
+++ b/src/libsyntax/parse/mod.rs
@@ -16,7 +16,7 @@ use rustc_data_structures::sync::{Lrc, Lock};
 use syntax_pos::{Span, SourceFile, FileName, MultiSpan};
 use log::debug;
 
-use rustc_data_structures::fx::FxHashSet;
+use rustc_data_structures::fx::{FxHashSet, FxHashMap};
 use std::borrow::Cow;
 use std::iter;
 use std::path::{Path, PathBuf};
@@ -47,6 +47,7 @@ pub struct ParseSess {
     included_mod_stack: Lock<Vec<PathBuf>>,
     source_map: Lrc<SourceMap>,
     pub buffered_lints: Lock<Vec<BufferedEarlyLint>>,
+    pub abiguous_block_expr_parse: Lock<FxHashMap<Span, Span>>,
 }
 
 impl ParseSess {
@@ -70,6 +71,7 @@ impl ParseSess {
             included_mod_stack: Lock::new(vec![]),
             source_map,
             buffered_lints: Lock::new(vec![]),
+            abiguous_block_expr_parse: Lock::new(FxHashMap::default()),
         }
     }