From 1c0b7ddda8bfabc9274f0d3bcb79be8eb8869f36 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Sun, 24 May 2020 10:03:08 -0400
Subject: [PATCH] fix regression in AST node iteration

the new iteration code caused an integer underflow for function
prototypes with no parameters. now fixed.
---
 lib/std/zig/ast.zig | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/std/zig/ast.zig b/lib/std/zig/ast.zig
index a257b9e1c..91aaf2909 100644
--- a/lib/std/zig/ast.zig
+++ b/lib/std/zig/ast.zig
@@ -706,7 +706,6 @@ pub const Node = struct {
             return null;
         }
 
-
         pub fn firstToken(self: *const VarDecl) TokenIndex {
             if (self.visib_token) |visib_token| return visib_token;
             if (self.thread_local_token) |thread_local_token| return thread_local_token;
@@ -1049,7 +1048,9 @@ pub const Node = struct {
                 i -= 1;
             }
 
-            const params_len = switch (self.paramsConst()[self.params_len - 1].param_type) {
+            const params_len: usize = if (self.params_len == 0)
+                0
+            else switch (self.paramsConst()[self.params_len - 1].param_type) {
                 .var_type, .type_expr => self.params_len,
                 .var_args => self.params_len - 1,
             };
@@ -2660,7 +2661,6 @@ pub const Node = struct {
             }
         };
 
-
         pub fn iterate(self: *const Asm, index: usize) ?*Node {
             var i = index;