Parse and infer tuple indices

crates/ra_syntax/src/syntax_error.rs

@@ -95,6 +95,7 @@ pub enum SyntaxErrorKind {
     InvalidSuffix,
     InvalidBlockAttr,
     InvalidMatchInnerAttr,
+    InvalidTupleIndexFormat,
 }
 
 impl fmt::Display for SyntaxErrorKind {
@@ -139,6 +140,9 @@ impl fmt::Display for SyntaxErrorKind {
             InvalidMatchInnerAttr => {
                 write!(f, "Inner attributes are only allowed directly after the opening brace of the match expression")
             }
+            InvalidTupleIndexFormat => {
+                write!(f, "Tuple (struct) field access is only allowed through decimal integers with no underscores or suffix")
+            }
             ParseError(msg) => write!(f, "{}", msg.0),
         }
     }