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`. */
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 --

View File

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