Merge pull request #5986 from NixOS/backport-5984-to-2.6-maintenance

[Backport 2.6-maintenance] Fix parsing of variable names that are a suffix of '__curPos'

src/libexpr/parser.y

@@ -405,7 +405,7 @@ expr_select
 expr_simple
   : ID {
       std::string_view s = "__curPos";
-      if (strncmp($1.p, s.data(), s.size()) == 0)
+      if ($1.l == s.size() && strncmp($1.p, s.data(), s.size()) == 0)
           $$ = new ExprPos(CUR_POS);
       else
           $$ = new ExprVar(CUR_POS, data->symbols.create($1));

tests/lang/eval-okay-regression-20220125.exp

@@ -0,0 +1 @@
+3

tests/lang/eval-okay-regression-20220125.nix

@@ -0,0 +1,2 @@
+((__curPosFoo: __curPosFoo) 1) + ((__curPosBar: __curPosBar) 2)
+