lix/doc/manual/rl-next/better-errors-in-nix-repl.md at 864ffff2ccfc9667b346bf6f541aa3a50eccd96c

Rebecca Turner 9e7e927837 Print top-level errors normally in nix repl

Previously, errors while printing values in `nix repl` would be printed
in `«error: ...»` brackets rather than displayed normally:

```
nix-repl> legacyPackages.aarch64-darwin.pythonPackages.APScheduler
«error: Package ‘python-2.7.18.7’ in /nix/store/6s0m1qc31zw3l3kq0q4wd5cp3lqpkq0q-source/pkgs/development/interpreters/python/cpython/2.7/default.nix:335 is marked as insecure, refusing to evaluate.»
```

Now, errors will be displayed normally if they're emitted at the
top-level of an expression:

```
nix-repl> legacyPackages.aarch64-darwin.pythonPackages.APScheduler
error:
       … in the condition of the assert statement
         at /nix/store/6s0m1qc31zw3l3kq0q4wd5cp3lqpkq0q-source/lib/customisation.nix:268:17:
          267|     in commonAttrs // {
          268|       drvPath = assert condition; drv.drvPath;
             |                 ^
          269|       outPath = assert condition; drv.outPath;

       … in the left operand of the OR (||) operator
         at /nix/store/6s0m1qc31zw3l3kq0q4wd5cp3lqpkq0q-source/pkgs/development/interpreters/python/passthrufun.nix:28:45:
           27|         if lib.isDerivation value then
           28|           lib.extendDerivation (valid value || throw "${name} should use `buildPythonPackage` or `toPythonModule` if it is to be part of the Python packages set.") {} value
             |                                             ^
           29|         else

       (stack trace truncated; use '--show-trace' to show the full trace)

       error: Package ‘python-2.7.18.7’ in /nix/store/6s0m1qc31zw3l3kq0q4wd5cp3lqpkq0q-source/pkgs/development/interpreters/python/cpython/2.7/default.nix:335 is marked as insecure, refusing to evaluate.
```

Errors emitted in nested structures (like e.g. when printing `nixpkgs`)
will still be printed in brackets.

Change-Id: I25aeddf08c017582718cb9772a677bf51b9fc2ad

2024-04-09 08:34:40 -07:00

1 KiB

Raw Blame History

synopsis	prs	cls
Concise error printing in `nix repl`	9928	811

Previously, if an element of a list or attribute set threw an error while evaluating, nix repl would print the entire error (including source location information) inline. This output was clumsy and difficult to parse:

nix-repl> { err = builtins.throw "uh oh!"; }
{ err = «error:
       … while calling the 'throw' builtin
         at «string»:1:9:
            1| { err = builtins.throw "uh oh!"; }
             |         ^

       error: uh oh!»; }

Now, only the error message is displayed, making the output much more readable.

nix-repl> { err = builtins.throw "uh oh!"; }
{ err = «error: uh oh!»; }

However, if the whole expression being evaluated throws an error, source locations and (if applicable) a stack trace are printed, just like you'd expect:

nix-repl> builtins.throw "uh oh!"
error:
       … while calling the 'throw' builtin
         at «string»:1:1:
            1| builtins.throw "uh oh!"
             | ^

       error: uh oh!

1 KiB Raw Blame History

1 KiB

Raw Blame History