libexpr: Don't use nix::dirOf in prim_dirOf

This gets us back to pre-2.23 behavior of this primop.
Done by inlining the code of `nix::dirOf` from 2.2-maintenance.

Author: xokdvium

src/libexpr/primops.cc

@@ -2022,8 +2022,13 @@ static void prim_dirOf(EvalState & state, const PosIdx pos, Value ** args, Value
         NixStringContext context;
         auto path = state.coerceToString(
             pos, *args[0], context, "while evaluating the first argument passed to 'builtins.dirOf'", false, false);
-        auto dir = dirOf(*path);
-        v.mkString(dir, context);
+        auto pos = path->rfind('/');
+        if (pos == path->npos)
+            v.mkStringMove(".", context);
+        else if (pos == 0)
+            v.mkStringMove("/", context);
+        else
+            v.mkString(path->substr(0, pos), context);
     }
 }
 

tests/functional/lang/eval-okay-builtins-dirOf.exp

@@ -1 +1 @@
-{ pathDoesntExistNested1 = /totallydoesntexistreally; pathDoesntExistNested2 = /totallydoesntexistreally/subdir1; pathDoesntExistRoot = /; pathRoot = /; stringEmpty = "."; stringMultipleSeps = "a"; stringNoSep = "."; stringRoot = "/"; stringRootA = "/"; stringRootSlash = "//"; stringRootSlashSlash = "///"; stringSingleDir = "a"; stringWithDot = "a/b/c/."; stringWithDotAndDotDot = "a/b/c/../."; stringWithDotAndDotDotSep2 = "a/b/c/../."; stringWithDotDot = "a/b/c/.."; stringWithDotDotSep2 = "a/b/c/.."; stringWithDotSep2 = "a/b/c/."; }
+{ pathDoesntExistNested1 = /totallydoesntexistreally; pathDoesntExistNested2 = /totallydoesntexistreally/subdir1; pathDoesntExistRoot = /; pathRoot = /; stringEmpty = "."; stringMultipleSeps = "a//"; stringNoSep = "."; stringRoot = "/"; stringRootA = "/"; stringRootSlash = "/"; stringRootSlashSlash = "//"; stringSingleDir = "a"; stringWithDot = "a/b/c/."; stringWithDotAndDotDot = "a/b/c/../."; stringWithDotAndDotDotSep2 = "a/b/c/.././"; stringWithDotDot = "a/b/c/.."; stringWithDotDotSep2 = "a/b/c/../"; stringWithDotSep2 = "a/b/c/./"; }