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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)
isList
isAttrs
substring
attrValues
concatLists
const
elem
generators
id
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
Type: traceSeqN :: Int -> a -> b -> b
*/
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;
/* 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 --
/* Evaluates 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, result}`,
- expected
- What was passed as `expected`
- result
- The actual `result` of the test
Used for regression testing of the functions in lib; see
tests.nix for more examples.
Important: Only attributes that start with `test` are executed.
- If you want to run only a subset of the tests add the attribute `tests = ["testName"];`
Example:
runTests {
testAndOk = {
expr = lib.and true false;
expected = false;
};
testAndFail = {
expr = lib.and true false;
expected = true;
};
}
->
[
{
name = "testAndFail";
expected = true;
result = false;
}
]
Type:
runTests :: {
tests = [ String ];
${testName} :: {
expr :: a;
expected :: a;
};
}
->
[
{
name :: String;
expected :: a;
result :: a;
}
]
*/
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; };
}
|