From bed8270c0cbaa3007621ad2f0e722abcefe79702 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 24 Jan 2022 15:18:18 +0100
Subject: [PATCH] Fix parsing of variable names that are a prefix of '__curPos'

Fixes

  $ nix-instantiate --parse -E 'x: with x; _'
  (x: (with x; __curPos))
---
 src/libexpr/parser.y                         | 3 ++-
 tests/lang/eval-okay-regression-20220122.exp | 1 +
 tests/lang/eval-okay-regression-20220122.nix | 1 +
 3 files changed, 4 insertions(+), 1 deletion(-)
 create mode 100644 tests/lang/eval-okay-regression-20220122.exp
 create mode 100644 tests/lang/eval-okay-regression-20220122.nix

diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index a3e713937..55f8abcb7 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -404,7 +404,8 @@ expr_select
 
 expr_simple
   : ID {
-      if (strncmp($1.p, "__curPos", $1.l) == 0)
+      std::string_view s = "__curPos";
+      if (strncmp($1.p, s.data(), s.size()) == 0)
           $$ = new ExprPos(CUR_POS);
       else
           $$ = new ExprVar(CUR_POS, data->symbols.create($1));
diff --git a/tests/lang/eval-okay-regression-20220122.exp b/tests/lang/eval-okay-regression-20220122.exp
new file mode 100644
index 000000000..00750edc0
--- /dev/null
+++ b/tests/lang/eval-okay-regression-20220122.exp
@@ -0,0 +1 @@
+3
diff --git a/tests/lang/eval-okay-regression-20220122.nix b/tests/lang/eval-okay-regression-20220122.nix
new file mode 100644
index 000000000..694e9a13b
--- /dev/null
+++ b/tests/lang/eval-okay-regression-20220122.nix
@@ -0,0 +1 @@
+((_: _) 1) + ((__: __) 2)