Error handling: Difference between revisions

(5 intermediate revisions by 2 users not shown)

Line 8:

lib.warn "This is a sample warning message."

{

config.warnings = [

config.warnings = (

# Some NixOS module: throw error, if services.foo.bar == true

(lib.optionals config.services.foo.bar "This is also a sample warning message, but invoked differently.")

lib.optionals config.services.foo.bar "This is also a sample warning message, but invoked differently."

];

);

}

</syntaxHighlight>

Line 19:

The nix language has a construct to help with printing messages.

* '''assert''': throw an error (see [https://nixos.org/manual/nix/stable/language/~~constructs~~.html?highlight=assert#assertions Nix manual: Assertions])

* '''assert''': throw an error (see [https://nixos.org/manual/nix/stable/language/syntax.html?highlight=assert#assertions Nix manual: Assertions])

The nix language also comes with some related [https://nixos.org/manual/nix/stable/language/builtins.html builtin functions]:

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To summarise debugging approaches discussed in this article, you can use <code>break</code> to debug nix code, <code>breakpointHook</code> to debug nix builds and interactive tools to debug NixOS tests.

To find the location where variables get defined, you can use the following tools:

For bare nix code, use <code>builtins.unsafeGetAttrPos

</code> ([https://github.com/NixOS/nix/blob/b17c4290cf61d8a0386817b87231762c175097c5/tests/lang/eval-okay-getattrpos.nix example]) which returns the line and column of where an attribute is defined. It is undocumented and considered bad practice.

(soon to come [https://github.com/NixOS/nixpkgs/pull/249243 github PR]): For NixOS options unsafeGetAttrPos doesn't work, but the module system itself records that information: to find the location of <code>config.networking.hostName</code>, use <code>:p options.networking.hostName.declarationPositions</code>.

== References ==

@@ Line 8: / Line 8: @@
 lib.warn "This is a sample warning message."
 {
-     config.warnings = [
+     config.warnings = (
        # Some NixOS module: throw error, if services.foo.bar == true
-       (lib.optionals config.services.foo.bar "This is also a sample warning message, but invoked differently.")
+       lib.optionals config.services.foo.bar "This is also a sample warning message, but invoked differently."
-     ];
+     );
 }
 </syntaxHighlight>
@@ Line 19: / Line 19: @@
 The nix language has a construct to help with printing messages.
-* '''assert''': throw an error (see [https://nixos.org/manual/nix/stable/language/constructs.html?highlight=assert#assertions Nix manual: Assertions])
+* '''assert''': throw an error (see [https://nixos.org/manual/nix/stable/language/syntax.html?highlight=assert#assertions Nix manual: Assertions])
 The nix language also comes with some related [https://nixos.org/manual/nix/stable/language/builtins.html builtin functions]:
@@ Line 68: / Line 68: @@
 To summarise debugging approaches discussed in this article, you can use <code>break</code> to debug nix code, <code>breakpointHook</code> to debug nix builds and interactive tools to debug NixOS tests.
+To find the location where variables get defined, you can use the following tools:
+For bare nix code, use <code>builtins.unsafeGetAttrPos
+</code> ([https://github.com/NixOS/nix/blob/b17c4290cf61d8a0386817b87231762c175097c5/tests/lang/eval-okay-getattrpos.nix example]) which returns the line and column of where an attribute is defined. It is undocumented and considered bad practice.
+(soon to come [https://github.com/NixOS/nixpkgs/pull/249243 github PR]): For NixOS options unsafeGetAttrPos doesn't work, but the module system itself records that information: to find the location of <code>config.networking.hostName</code>, use <code>:p options.networking.hostName.declarationPositions</code>.
 == References ==