From 4dcb183af31d5cb33b6ef8e581e77d1c892a58b9 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Thu, 19 Nov 2020 20:59:36 +0100
Subject: [PATCH] AttrCursor::getStringWithContext(): Force re-evaluation if
 the cached context is not valid

Fixes #4236.
---
 src/libexpr/eval-cache.cc | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/libexpr/eval-cache.cc b/src/libexpr/eval-cache.cc
index 381344b4002..7b025be2342 100644
--- a/src/libexpr/eval-cache.cc
+++ b/src/libexpr/eval-cache.cc
@@ -525,8 +525,17 @@ string_t AttrCursor::getStringWithContext()
             cachedValue = root->db->getAttr(getKey(), root->state.symbols);
         if (cachedValue && !std::get_if<placeholder_t>(&cachedValue->second)) {
             if (auto s = std::get_if<string_t>(&cachedValue->second)) {
-                debug("using cached string attribute '%s'", getAttrPathStr());
-                return *s;
+                bool valid = true;
+                for (auto & c : s->second) {
+                    if (!root->state.store->isValidPath(root->state.store->parseStorePath(c.first))) {
+                        valid = false;
+                        break;
+                    }
+                }
+                if (valid) {
+                    debug("using cached string attribute '%s'", getAttrPathStr());
+                    return *s;
+                }
             } else
                 throw TypeError("'%s' is not a string", getAttrPathStr());
         }