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