Fix string for array access suggestion

Author: varkor

src/librustc_typeck/check/mod.rs

@@ -3372,7 +3372,9 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                             len.assert_usize(self.tcx),
                             field.as_str().parse::<u64>()
                         ) {
-                            let base = self.tcx.hir().node_to_pretty_string(base.id);
+                            let base = self.tcx.sess.source_map()
+                                .span_to_snippet(base.span)
+                                .unwrap_or_else(|_| self.tcx.hir().node_to_pretty_string(base.id));
                             let help = "instead of using tuple indexing, use array indexing";
                             let suggestion = format!("{}[{}]", base, field);
                             let applicability = if len < user_index {

src/test/ui/parenthesised-deref-suggestion.rs

@@ -5,4 +5,7 @@ struct Session {
 fn main() {
     let sess: &Session = &Session { opts: 0 };
     (sess as *const Session).opts; //~ ERROR no field `opts` on type `*const Session`
+
+    let x = [0u32];
+    (x as [u32; 1]).0; //~ ERROR no field `0` on type `[u32; 1]`
 }

src/test/ui/parenthesised-deref-suggestion.stderr

@@ -7,6 +7,15 @@ help: `(sess as *const Session)` is a raw pointer; try dereferencing it
    |
 LL |     (*(sess as *const Session)).opts; //~ ERROR no field `opts` on type `*const Session`
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0609]: no field `0` on type `[u32; 1]`
+  --> $DIR/parenthesised-deref-suggestion.rs:10:21
+   |
+LL |     (x as [u32; 1]).0; //~ ERROR no field `0` on type `[u32; 1]`
+   |     ----------------^
+   |     |
+   |     help: instead of using tuple indexing, use array indexing: `(x as [u32; 1])[0]`
+
 error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0609`.