lib/debug: add traceFnSeqN

Immensely helpful when you want to see the changes a function makes to
its value as it passes through.

Example:

```
$ nix-instantiate --strict --eval -E '(with import ./lib; traceFnSeqN 2 "id" (x: x) { a.b.c = 3; })'
trace: {
  fn = "id";
  from = {
    a = {
      b = {…};
    };
  };
  to = {
    a = {
      b = {…};
    };
  };
}
{ a = { b = { c = 3; }; }; }
```
This commit is contained in:
Profpatsch 2021-01-24 11:33:41 +01:00
parent ec334a1b01
commit 41e13149f7
2 changed files with 23 additions and 1 deletions

View file

@ -148,6 +148,28 @@ rec {
/* A combination of `traceVal` and `traceSeqN`. */ /* A combination of `traceVal` and `traceSeqN`. */
traceValSeqN = traceValSeqNFn id; traceValSeqN = traceValSeqNFn id;
/* Trace the input and output of a function `f` named `name`,
both down to `depth`.
This is useful for adding around a function call,
to see the before/after of values as they are transformed.
Example:
traceFnSeqN 2 "id" (x: x) { a.b.c = 3; }
trace: { fn = "id"; from = { a.b = {}; }; to = { a.b = {}; }; }
=> { a.b.c = 3; }
*/
traceFnSeqN = depth: name: f: v:
let res = f v;
in lib.traceSeqN
(depth + 1)
{
fn = name;
from = v;
to = res;
}
res;
# -- TESTING -- # -- TESTING --

View file

@ -130,7 +130,7 @@ let
assertMsg assertOneOf; assertMsg assertOneOf;
inherit (self.debug) addErrorContextToAttrs traceIf traceVal traceValFn inherit (self.debug) addErrorContextToAttrs traceIf traceVal traceValFn
traceXMLVal traceXMLValMarked traceSeq traceSeqN traceValSeq traceXMLVal traceXMLValMarked traceSeq traceSeqN traceValSeq
traceValSeqFn traceValSeqN traceValSeqNFn traceShowVal traceValSeqFn traceValSeqN traceValSeqNFn traceFnSeqN traceShowVal
traceShowValMarked showVal traceCall traceCall2 traceCall3 traceShowValMarked showVal traceCall traceCall2 traceCall3
traceValIfNot runTests testAllTrue traceCallXml attrNamesToStr; traceValIfNot runTests testAllTrue traceCallXml attrNamesToStr;
inherit (self.misc) maybeEnv defaultMergeArg defaultMerge foldArgs inherit (self.misc) maybeEnv defaultMergeArg defaultMerge foldArgs