Error handling: Difference between revisions

Line 11:

The nix language has some constructs to help with printing messages.

- assert: throw an error [2]

* '''assert''': throw an error [2]

The nix language already comes with some usefult builtin functions [3]:

- throw: throw an error with a message

* '''throw''': throw an error with a message

- abort: same as throw, but always stop evaluation

* '''abort''': same as throw, but always stop evaluation

- trace: print to stderr

* '''trace''': print to stderr

- traceVerbose: print, but only when in --trace-verbose mode

* '''traceVerbose''': print, but only when in --trace-verbose mode

- break: breakpoint when in --debugger mode

* '''break''': breakpoint when in --debugger mode

- tryEval: catch throws and asserts

* '''tryEval''': catch throws and asserts

Commonly, assert is combined with throw to generate meaningful error messages: assert condition || throw "message"; This pattern is essentially how lib.assertMsg works (see Sec. nixpkgs). [1]

Line 28:

There are three main facilities for printing errors and do print debugging in nixpkgs:

- lib.trivial.* [6]

* lib.trivial.* [6]

- lib.throwIf and throwIfNot

* lib.throwIf and throwIfNot

- lib.warn, warnIf and warnIfNot

* lib.warn, warnIf and warnIfNot

- lib.debug.*: tracing functions with some pretty printing [7, 9]

* lib.debug.*: tracing functions with some pretty printing [7, 9]

- lib.asserts.*: assert functions [8]

* lib.asserts.*: assert functions [8]

These facilities also expose their attributes directly via lib.* (e.g. lib.throwIf).

Line 42:

The NixOS module system again wraps these library functions and makes them available via module options: [11, 10]

- config.warnings = [];

* config.warnings = [];

- config.assertions = [];

* config.assertions = [];

An example for a debugging facility in NixOS is running NixOS tests interactively (see [13]).

@@ Line 11: / Line 11: @@
 The nix language has some constructs to help with printing messages.
-- assert: throw an error [2]
+* '''assert''': throw an error [2]
 The nix language already comes with some usefult builtin functions [3]:
-- throw: throw an error with a message
+* '''throw''': throw an error with a message
-- abort: same as throw, but always stop evaluation
+* '''abort''': same as throw, but always stop evaluation
-- trace: print to stderr
+* '''trace''': print to stderr
-- traceVerbose: print, but only when in --trace-verbose mode
+* '''traceVerbose''': print, but only when in --trace-verbose mode
-- break: breakpoint when in --debugger mode
+* '''break''': breakpoint when in --debugger mode
-- tryEval: catch throws and asserts
+* '''tryEval''': catch throws and asserts
 Commonly, assert is combined with throw to generate meaningful error messages: assert condition || throw "message"; This pattern is essentially how lib.assertMsg works (see Sec. nixpkgs). [1]
@@ Line 28: / Line 28: @@
 There are three main facilities for printing errors and do print debugging in nixpkgs:
-- lib.trivial.* [6]
+* lib.trivial.* [6]
-     - lib.throwIf and throwIfNot
+     * lib.throwIf and throwIfNot
-     - lib.warn, warnIf and warnIfNot
+     * lib.warn, warnIf and warnIfNot
-- lib.debug.*: tracing functions with some pretty printing [7, 9]
+* lib.debug.*: tracing functions with some pretty printing [7, 9]
-- lib.asserts.*: assert functions [8]
+* lib.asserts.*: assert functions [8]
 These facilities also expose their attributes directly via lib.* (e.g. lib.throwIf).
@@ Line 42: / Line 42: @@
 The NixOS module system again wraps these library functions and makes them available via module options: [11, 10]
-- config.warnings = [];
+* config.warnings = [];
-- config.assertions = [];
+* config.assertions = [];
 An example for a debugging facility in NixOS is running NixOS tests interactively (see [13]).