Merge pull request #9753 from 9999years/print-value-on-type-error

Print the value in `value is X while a Y is expected` error

(cherry picked from commit 5f72a97092da6af28a7d2b2a50d74e9d34fae7e1)
Change-Id: Idb4bc903ae59a0f5b6fb3b1da4d47970fe0a6efe

src/libexpr/eval-inline.hh

@@ -1,6 +1,7 @@
 #pragma once
 ///@file
 
+#include "print.hh"
 #include "eval.hh"
 
 namespace nix {
@@ -114,7 +115,10 @@ inline void EvalState::forceAttrs(Value & v, Callable getPos, std::string_view e
     PosIdx pos = getPos();
     forceValue(v, pos);
     if (v.type() != nAttrs) {
-        error("value is %1% while a set was expected", showType(v)).withTrace(pos, errorCtx).debugThrow<TypeError>();
+        error("expected a set but found %1%: %2%",
+              showType(v),
+              ValuePrinter(*this, v, errorPrintOptions))
+            .withTrace(pos, errorCtx).debugThrow<TypeError>();
     }
 }
 
@@ -124,7 +128,10 @@ inline void EvalState::forceList(Value & v, const PosIdx pos, std::string_view e
 {
     forceValue(v, pos);
     if (!v.isList()) {
-        error("value is %1% while a list was expected", showType(v)).withTrace(pos, errorCtx).debugThrow<TypeError>();
+        error("expected a list but found %1%: %2%",
+              showType(v),
+              ValuePrinter(*this, v, errorPrintOptions))
+            .withTrace(pos, errorCtx).debugThrow<TypeError>();
     }
 }