Merge changes I07d2da41,I864d7340,I86612c64 into main

* changes:
  Change error messages about 'invalid paths' to 'path does not exist'.
  Add a clearer error message for InvalidPathError during evaluation
  Harmonise the Store::queryPathInfoUncached interface

src/libexpr/eval-error.hh

@@ -47,12 +47,16 @@ MakeError(MissingArgumentError, EvalError);
 MakeError(RestrictedPathError, Error);
 MakeError(InfiniteRecursionError, EvalError);
 
+/**
+ * Represents an exception due to an invalid path; that is, it does not exist.
+ * It corresponds to `!Store::validPath()`.
+ */
 struct InvalidPathError : public EvalError
 {
 public:
     Path path;
     InvalidPathError(EvalState & state, const Path & path)
-        : EvalError(state, "path '%s' is not valid", path)
+        : EvalError(state, "path '%s' did not exist in the store during evaluation", path)
     {
     }
 };

src/libexpr/primops.cc

@@ -383,7 +383,8 @@ void prim_exec(EvalState & state, const PosIdx pos, Value * * args, Value & v)
     try {
         auto _ = state.realiseContext(context); // FIXME: Handle CA derivations
     } catch (InvalidPathError & e) {
-        state.error<EvalError>("cannot execute '%1%', since path '%2%' is not valid", program, e.path).atPos(pos).debugThrow();
+        e.addTrace(state.positions[pos], "while realising the context for builtins.exec");
+        throw;
     }
 
     auto output = runProgram(program, true, commandArgs);