lib/debug.nix overhaul #38368

Profpatsch · 2018-04-03T07:00:42Z

The debug module is very useful for day-to-day nix programming, but hasn’t seen a lot of care and aquired quite a lot of cruft.

Main changes:

add *Val*Fn group of functions
remove deprecated strict function
deprecate the showVal group of functions because traceSeqN should be strictly more general
deprecate the Xml-group of functions, because they are mostly trivial and/or overly specific
deprecate traceValIfNot and addErrorContextToAttrs
document the module and tracing functions

More detailed reasoning is included in each commit description.

makefu · 2018-04-03T08:28:29Z

I think it would be nice to have a consistent write-up (or at least a reference entry) on how to use these functions, not only in the comment field above the code but in the manual itself. This is related to NixOS/nix#701 and
NixOS/nix#702

Profpatsch · 2018-04-03T08:52:46Z

@makefu I can mention the debug module in the manual (similar to how generators is mentioned), but would rather not duplicate the docstrings (because that will go out of sync sooner rather than later).

If there’s a debugging tutorial, it should most likely go into a new chapter of the nix pills, which have been designated as our official tutorial as far as I can see.

makefu · 2018-04-03T10:05:49Z

@Profpatsch For newcomers that kind of "documentation" is far from optimal. When you start with nix and nixpkgs it is not very obvious to look for solutions inside the implementation source code.

IMHO the nixpkgs libs need a reference similar to what we have for the modules and packages, however to solve this is out of scope for this PR which looks fine.

grahamc · 2018-04-03T10:58:58Z

lib/default.nix

@@ -117,7 +117,7 @@ let
      traceXMLVal traceXMLValMarked traceSeq traceSeqN traceValSeq
      traceValSeqFn traceValSeqN traceValSeqNFn traceShowVal
      traceShowValMarked showVal traceCall traceCall2 traceCall3
-      traceValIfNot runTests testAllTrue strict traceCallXml
+      traceValIfNot runTests testAllTrue traceCallXml


Needs release notes.

grahamc · 2018-04-03T11:01:00Z

lib/debug.nix

@@ -56,19 +56,25 @@ rec {
  traceShowVal = x: trace (showVal x) x;
  traceShowValMarked = str: x: trace (str + showVal x) x;
  attrNamesToStr = a: lib.concatStringsSep "; " (map (x: "${x}=") (attrNames a));
-  showVal = x:


It isn't clear to me that traceSeqN is an improvement over showVal for this use case. Can you provide some examples of the two's output?

showVal displays the value with one layer of depth. traceValSeqN 1 does the same, traceValSeqN 2 does the same for a depth of two layers and so forth.

To be fair, the display is different, but I don’t think there is any information in showVal that cannot be seen in the output of traceValSeqN.

grahamc · 2018-04-03T11:04:00Z

lib/debug.nix

+    trace ( "Warning: `traceXMLValMarked` is deprecated "
+          + "and will be removed in the next release." )
+    (trace (str + builtins.toXML x) x);
+


These need release notes.

grahamc · 2018-04-03T11:05:03Z

nixos/modules/misc/nixpkgs.nix

@@ -33,7 +33,7 @@ let
  configType = mkOptionType {
    name = "nixpkgs-config";
    description = "nixpkgs config";
-    check = traceValIfNot isConfig;
+    check = x: if isConfig x then true else lib.traceSeqN 1 x false;


I prefer the named one, actually.

It’s locally let-named in the rebased commit.

Profpatsch · 2018-04-03T11:09:16Z

@makefu Added an initial section to the manual in the last commit. It is more of a stub for now (but at least users now find something when they search for debug (in the right manual)).

grahamc · 2018-04-03T11:09:19Z

I think all the functions which have been deprecated need:

release notes
their deprecation warnings to include what to replace them with

Profpatsch · 2018-04-03T12:06:34Z

Added release notes & replacement instructions in the last commit.

Mic92 · 2018-04-09T08:05:12Z

doc/functions.xml

+<section xml:id="sec-debug">
+  <title>Debugging Nix Expressions</title>
+
+  <para>Nix is a unityped, dynamic language, this means every value can


unityped or untyped?

Neither of those are true 😁

@shlevy Hm, why is nix not unityped?

[] and {} are of different types. The fact that those are checked at eval time (which, FWIW, can be seen as compile time with respect to the underlying .drv outputs...) doesn't make them not typed!

Ah, well, I see eval time more as execution time.

Being able to modify the value on-the-fly before printing is very useful in practice.

The grace period was long enough.

The code is re-implemented in terms of `generators.toPretty`, but is strictly less general than `traceValSeqN`, so we deprecate it.

`attrNamesToStr` is very specific (and pretty trivial), so it doesn’t make sense to have it in the library. `traceXMLVal(Marked)` are just a builtin and `trace` and not very useful in general (trace output should not be parsed anyway).

The function is only used in exactly one module and overly specific (`c` must be a true predicate for `x`, if not, a specific trace is called).

The function isn’t used anywhere and `addErrorContext` is an undocumented builtin. The builtin is explicitely qualified at its two uses in the module system.

Incompletely documented, and a FIXME/bug that has been there for years.

Reason: has overhauled the module quite substantially.

It is more of a stub for now, but at least points to the right file.

for every deprecated function.

Profpatsch · 2018-04-13T15:47:56Z

I rebased it to remove the release note merge conflicts.

Profpatsch · 2018-04-27T17:00:44Z

Merging because no further feedback.
We can roll back selectively if something breaks (although nothing should, since these are debug functions).

traceShowVal traceShowValMarked attrNamesToStr showVal traceXMLVal traceXMLValMarked traceCall traceCall2 traceCall3 traceValIfNot addErrorContextToAttrs traceCallXml they were deprecated in NixOS#38368

Profpatsch requested review from edolstra and nbp as code owners April 3, 2018 07:00

Profpatsch assigned grahamc and shlevy Apr 3, 2018

GrahamcOfBorg added 6.topic: nixos 6.topic: policy discussion 6.topic: vim 8.has: module (update) labels Apr 3, 2018

Profpatsch force-pushed the lib-debug-overhaul branch from 8b29d89 to e96069d Compare April 3, 2018 07:09

GrahamcOfBorg added 10.rebuild-darwin: 0 10.rebuild-linux: 0 labels Apr 3, 2018

grahamc reviewed Apr 3, 2018

View reviewed changes

GrahamcOfBorg added the 8.has: documentation label Apr 3, 2018

Profpatsch force-pushed the lib-debug-overhaul branch from 1817a0f to d136321 Compare April 3, 2018 12:05

GrahamcOfBorg added the 8.has: changelog label Apr 3, 2018

Mic92 reviewed Apr 9, 2018

View reviewed changes

shlevy removed their assignment Apr 9, 2018

Profpatsch added 4 commits April 13, 2018 17:27

lib/debug: add traceValFn, traceValSeqFn, traceValSeqNFn

9ae3511

Being able to modify the value on-the-fly before printing is very useful in practice.

lib/debug: remove the deprecated strict function

2cc7cac

The grace period was long enough.

lib/debug: deprecate & modernize showVal

32ea43e

The code is re-implemented in terms of `generators.toPretty`, but is strictly less general than `traceValSeqN`, so we deprecate it.

Profpatsch added 8 commits April 13, 2018 17:27

lib/debug: deprecate traceValIfNot

86b498a

The function is only used in exactly one module and overly specific (`c` must be a true predicate for `x`, if not, a specific trace is called).

lib/debug: fix use-sites of deprecated debug functions

8943858

lib/debug: deprecate addErrorContextToAttrs

1fa0d41

The function isn’t used anywhere and `addErrorContext` is an undocumented builtin. The builtin is explicitely qualified at its two uses in the module system.

lib/debug: deprecate traceCallXml

a79e8e2

Incompletely documented, and a FIXME/bug that has been there for years.

lib/debug: document module & functions, prune imports

943a631

CODEOWNERS: add Profpatsch to lib/debug.nix

902fcf6

Reason: has overhauled the module quite substantially.

docs: initial manual entry for lib/debug.nix

b577529

It is more of a stub for now, but at least points to the right file.

lib/debug: add replacement instructions & release notes

0d3d0fd

for every deprecated function.

Profpatsch force-pushed the lib-debug-overhaul branch from d136321 to 0d3d0fd Compare April 13, 2018 15:37

Profpatsch merged commit 900cec7 into NixOS:master Apr 27, 2018

Artturin mentioned this pull request Oct 6, 2022

lib/debug: throw functions that have been deprecated since 2018 #194780

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lib/debug.nix overhaul #38368

lib/debug.nix overhaul #38368

Profpatsch commented Apr 3, 2018 •

edited

makefu commented Apr 3, 2018

Profpatsch commented Apr 3, 2018 •

edited

makefu commented Apr 3, 2018

grahamc Apr 3, 2018

Profpatsch Apr 3, 2018

grahamc Apr 3, 2018

Profpatsch Apr 3, 2018

grahamc Apr 3, 2018

Profpatsch Apr 3, 2018

grahamc Apr 3, 2018

Profpatsch Apr 3, 2018

Profpatsch commented Apr 3, 2018

grahamc commented Apr 3, 2018

Profpatsch commented Apr 3, 2018

Mic92 Apr 9, 2018

shlevy Apr 9, 2018

Profpatsch Apr 9, 2018

shlevy Apr 9, 2018 •

edited

Profpatsch Apr 9, 2018

Profpatsch commented Apr 13, 2018 •

edited

Profpatsch commented Apr 27, 2018

lib/debug.nix overhaul #38368

lib/debug.nix overhaul #38368

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Profpatsch commented Apr 3, 2018 • edited

makefu commented Apr 3, 2018

Profpatsch commented Apr 3, 2018 • edited

makefu commented Apr 3, 2018

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Profpatsch commented Apr 3, 2018

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Profpatsch commented Apr 13, 2018 • edited

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Profpatsch commented Apr 13, 2018 •

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