Nix flakes should not cache evaluation errors #3872
Description
Describe the bug
Currently error messages are only showed the first time they appear.
After that the error message looks like this:
$ sudo nixos-rebuild switch
building the system configuration...
error: --- EvalError -------------------------------------------------------------------------- nix
cached failure of attribute 'nixosConfigurations.turingmachine.config.system.build.toplevel.drvPath'
The problem is that the error message of the first time might be no longer visible,
so users would get stuck not knowing what its going on.
Steps To Reproduce
- Create an invalid nixos configuration i.e. add two conflicting options (but valid nix syntax)
- Run
nixos-rebuild switch:
error: --- ThrownError --------------------------------------------------------------------------- nix
The option `system.nixos.versionSuffix' has conflicting definitions, in `<unknown-file>' and `<unknown-file>'.
(use '--show-trace' to show detailed location information)
- Run
nixos-rebuild switchagain:
building the system configuration...
error: --- EvalError -------------------------------------------------------------------------- nix
cached failure of attribute 'nixosConfigurations.turingmachine.config.system.build.toplevel.drvPath'
Expected behavior
It should not cache evaluation failures and show me the message agin
nix-env --version output
$ nix-env --version
nix-env (Nix) 2.4pre20200721_ff314f1