/* 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; }; }