From d3c428413367a87ab2d27abe9c7f3c379eb12e1c Mon Sep 17 00:00:00 2001
From: regnat <rg@regnat.ovh>
Date: Tue, 5 Jan 2021 10:01:22 +0100
Subject: [PATCH] Make the error message for missing outputs more useful

Don't only show the name of the output, but also the derivation to which
this output belongs (as otherwise it's very hard to track back what went
wrong)
---
 src/libstore/store-api.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 01e2fcc7b..9da415c42 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -394,7 +394,7 @@ OutputPathMap Store::queryDerivationOutputMap(const StorePath & path) {
     OutputPathMap result;
     for (auto & [outName, optOutPath] : resp) {
         if (!optOutPath)
-            throw Error("output '%s' has no store path mapped to it", outName);
+            throw Error("output '%s' of derivation '%s' has no store path mapped to it", outName, printStorePath(path));
         result.insert_or_assign(outName, *optOutPath);
     }
     return result;