mirror of
https://github.com/NixOS/nixpkgs.git
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41e13149f7
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; }; }; }
```
292 lines
8.8 KiB
Nix
292 lines
8.8 KiB
Nix
/* Collection of functions useful for debugging
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broken nix expressions.
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* `trace`-like functions take two values, print
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the first to stderr and return the second.
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* `traceVal`-like functions take one argument
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which both printed and returned.
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* `traceSeq`-like functions fully evaluate their
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traced value before printing (not just to “weak
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head normal form” like trace does by default).
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* Functions that end in `-Fn` take an additional
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function as their first argument, which is applied
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to the traced value before it is printed.
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*/
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{ lib }:
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let
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inherit (lib)
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isInt
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attrNames
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isList
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isAttrs
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substring
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addErrorContext
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attrValues
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concatLists
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concatStringsSep
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const
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elem
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generators
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head
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id
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isDerivation
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isFunction
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mapAttrs
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trace;
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in
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rec {
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# -- TRACING --
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/* Conditionally trace the supplied message, based on a predicate.
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Type: traceIf :: bool -> string -> a -> a
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Example:
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traceIf true "hello" 3
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trace: hello
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=> 3
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*/
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traceIf =
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# Predicate to check
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pred:
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# Message that should be traced
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msg:
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# Value to return
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x: if pred then trace msg x else x;
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/* Trace the supplied value after applying a function to it, and
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return the original value.
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Type: traceValFn :: (a -> b) -> a -> a
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Example:
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traceValFn (v: "mystring ${v}") "foo"
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trace: mystring foo
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=> "foo"
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*/
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traceValFn =
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# Function to apply
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f:
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# Value to trace and return
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x: trace (f x) x;
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/* Trace the supplied value and return it.
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Type: traceVal :: a -> a
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Example:
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traceVal 42
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# trace: 42
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=> 42
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*/
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traceVal = traceValFn id;
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/* `builtins.trace`, but the value is `builtins.deepSeq`ed first.
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Type: traceSeq :: a -> b -> b
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Example:
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trace { a.b.c = 3; } null
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trace: { a = <CODE>; }
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=> null
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traceSeq { a.b.c = 3; } null
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trace: { a = { b = { c = 3; }; }; }
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=> null
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*/
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traceSeq =
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# The value to trace
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x:
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# The value to return
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y: trace (builtins.deepSeq x x) y;
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/* Like `traceSeq`, but only evaluate down to depth n.
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This is very useful because lots of `traceSeq` usages
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lead to an infinite recursion.
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Example:
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traceSeqN 2 { a.b.c = 3; } null
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trace: { a = { b = {…}; }; }
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=> null
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*/
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traceSeqN = depth: x: y:
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let snip = v: if isList v then noQuotes "[…]" v
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else if isAttrs v then noQuotes "{…}" v
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else v;
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noQuotes = str: v: { __pretty = const str; val = v; };
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modify = n: fn: v: if (n == 0) then fn v
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else if isList v then map (modify (n - 1) fn) v
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else if isAttrs v then mapAttrs
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(const (modify (n - 1) fn)) v
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else v;
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in trace (generators.toPretty { allowPrettyValues = true; }
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(modify depth snip x)) y;
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/* A combination of `traceVal` and `traceSeq` that applies a
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provided function to the value to be traced after `deepSeq`ing
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it.
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*/
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traceValSeqFn =
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# Function to apply
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f:
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# Value to trace
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v: traceValFn f (builtins.deepSeq v v);
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/* A combination of `traceVal` and `traceSeq`. */
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traceValSeq = traceValSeqFn id;
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/* A combination of `traceVal` and `traceSeqN` that applies a
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provided function to the value to be traced. */
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traceValSeqNFn =
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# Function to apply
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f:
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depth:
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# Value to trace
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v: traceSeqN depth (f v) v;
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/* A combination of `traceVal` and `traceSeqN`. */
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traceValSeqN = traceValSeqNFn id;
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/* Trace the input and output of a function `f` named `name`,
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both down to `depth`.
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This is useful for adding around a function call,
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to see the before/after of values as they are transformed.
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Example:
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traceFnSeqN 2 "id" (x: x) { a.b.c = 3; }
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trace: { fn = "id"; from = { a.b = {…}; }; to = { a.b = {…}; }; }
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=> { a.b.c = 3; }
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*/
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traceFnSeqN = depth: name: f: v:
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let res = f v;
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in lib.traceSeqN
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(depth + 1)
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{
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fn = name;
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from = v;
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to = res;
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}
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res;
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# -- TESTING --
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/* Evaluate a set of tests. A test is an attribute set `{expr,
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expected}`, denoting an expression and its expected result. The
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result is a list of failed tests, each represented as `{name,
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expected, actual}`, denoting the attribute name of the failing
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test and its expected and actual results.
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Used for regression testing of the functions in lib; see
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tests.nix for an example. Only tests having names starting with
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"test" are run.
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Add attr { tests = ["testName"]; } to run these tests only.
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*/
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runTests =
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# Tests to run
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tests: concatLists (attrValues (mapAttrs (name: test:
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let testsToRun = if tests ? tests then tests.tests else [];
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in if (substring 0 4 name == "test" || elem name testsToRun)
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&& ((testsToRun == []) || elem name tests.tests)
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&& (test.expr != test.expected)
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then [ { inherit name; expected = test.expected; result = test.expr; } ]
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else [] ) tests));
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/* Create a test assuming that list elements are `true`.
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Example:
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{ testX = allTrue [ true ]; }
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*/
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testAllTrue = expr: { inherit expr; expected = map (x: true) expr; };
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# -- DEPRECATED --
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traceShowVal = x: trace (showVal x) x;
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traceShowValMarked = str: x: trace (str + showVal x) x;
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attrNamesToStr = a:
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trace ( "Warning: `attrNamesToStr` is deprecated "
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+ "and will be removed in the next release. "
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+ "Please use more specific concatenation "
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+ "for your uses (`lib.concat(Map)StringsSep`)." )
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(concatStringsSep "; " (map (x: "${x}=") (attrNames a)));
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showVal =
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trace ( "Warning: `showVal` is deprecated "
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+ "and will be removed in the next release, "
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+ "please use `traceSeqN`" )
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(let
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modify = v:
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let pr = f: { __pretty = f; val = v; };
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in if isDerivation v then pr
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(drv: "<δ:${drv.name}:${concatStringsSep ","
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(attrNames drv)}>")
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else if [] == v then pr (const "[]")
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else if isList v then pr (l: "[ ${go (head l)}, … ]")
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else if isAttrs v then pr
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(a: "{ ${ concatStringsSep ", " (attrNames a)} }")
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else v;
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go = x: generators.toPretty
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{ allowPrettyValues = true; }
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(modify x);
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in go);
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traceXMLVal = x:
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trace ( "Warning: `traceXMLVal` is deprecated "
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+ "and will be removed in the next release. "
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+ "Please use `traceValFn builtins.toXML`." )
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(trace (builtins.toXML x) x);
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traceXMLValMarked = str: x:
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trace ( "Warning: `traceXMLValMarked` is deprecated "
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+ "and will be removed in the next release. "
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+ "Please use `traceValFn (x: str + builtins.toXML x)`." )
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(trace (str + builtins.toXML x) x);
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# trace the arguments passed to function and its result
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# maybe rewrite these functions in a traceCallXml like style. Then one function is enough
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traceCall = n: f: a: let t = n2: x: traceShowValMarked "${n} ${n2}:" x; in t "result" (f (t "arg 1" a));
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traceCall2 = n: f: a: b: let t = n2: x: traceShowValMarked "${n} ${n2}:" x; in t "result" (f (t "arg 1" a) (t "arg 2" b));
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traceCall3 = n: f: a: b: c: let t = n2: x: traceShowValMarked "${n} ${n2}:" x; in t "result" (f (t "arg 1" a) (t "arg 2" b) (t "arg 3" c));
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traceValIfNot = c: x:
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trace ( "Warning: `traceValIfNot` is deprecated "
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+ "and will be removed in the next release. "
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+ "Please use `if/then/else` and `traceValSeq 1`.")
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(if c x then true else traceSeq (showVal x) false);
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addErrorContextToAttrs = attrs:
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trace ( "Warning: `addErrorContextToAttrs` is deprecated "
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+ "and will be removed in the next release. "
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+ "Please use `builtins.addErrorContext` directly." )
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(mapAttrs (a: v: addErrorContext "while evaluating ${a}" v) attrs);
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# example: (traceCallXml "myfun" id 3) will output something like
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# calling myfun arg 1: 3 result: 3
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# this forces deep evaluation of all arguments and the result!
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# note: if result doesn't evaluate you'll get no trace at all (FIXME)
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# args should be printed in any case
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traceCallXml = a:
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trace ( "Warning: `traceCallXml` is deprecated "
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+ "and will be removed in the next release. "
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+ "Please complain if you use the function regularly." )
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(if !isInt a then
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traceCallXml 1 "calling ${a}\n"
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else
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let nr = a;
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in (str: expr:
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if isFunction expr then
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(arg:
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traceCallXml (builtins.add 1 nr) "${str}\n arg ${builtins.toString nr} is \n ${builtins.toXML (builtins.seq arg arg)}" (expr arg)
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)
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else
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let r = builtins.seq expr expr;
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in trace "${str}\n result:\n${builtins.toXML r}" r
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));
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}
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