Index expressions rendered the index: subexpression as the id, instead of actually showing the content of the subexpression

This meant the content of the subexpression was completely missing from tree view (as the id did not reference anything)

Author: AlexCeleste

compiler/rustc_mir_build/src/thir/print.rs

@@ -397,9 +397,10 @@ impl<'a, 'tcx> ThirPrinter<'a, 'tcx> {
             }
             Index { lhs, index } => {
                 print_indented!(self, "Index {", depth_lvl);
-                print_indented!(self, format!("index: {:?}", index), depth_lvl + 1);
                 print_indented!(self, "lhs:", depth_lvl + 1);
                 self.print_expr(*lhs, depth_lvl + 2);
+                print_indented!(self, "index:", depth_lvl + 1);
+                self.print_expr(*index, depth_lvl + 2);
                 print_indented!(self, "}", depth_lvl);
             }
             VarRef { id } => {

tests/ui/thir-print/thir-tree-array-index.rs

@@ -0,0 +1,22 @@
+//@ check-pass
+//@ compile-flags: -Zunpretty=thir-tree
+
+fn index(x: usize) -> usize { x }
+
+fn indexing(x: usize) -> usize {
+  let a1: [usize; 5] = [1, 2, 3, 4, 5];
+  let a2: [usize; 5] = [x; 5];
+
+  a1[0];
+  a2[1];
+
+  a1[x];
+  a2[x + 2];
+
+  a1[a2[x] + a2[x - 3]];
+  a2[index (x + 1) - x];
+
+  0
+}
+
+fn main() {}