/** 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. # Inputs `pred` : Predicate to check `msg` : Message that should be traced `x` : Value to return # Type ``` traceIf :: bool -> string -> a -> a ``` # Examples :::{.example} ## `lib.debug.traceIf` usage example ```nix traceIf true "hello" 3 trace: hello => 3 ``` ::: */ traceIf = pred: msg: x: if pred then trace msg x else x; /** Trace the supplied value after applying a function to it, and return the original value. # Inputs `f` : Function to apply `x` : Value to trace and return # Type ``` traceValFn :: (a -> b) -> a -> a ``` # Examples :::{.example} ## `lib.debug.traceValFn` usage example ```nix traceValFn (v: "mystring ${v}") "foo" trace: mystring foo => "foo" ``` ::: */ traceValFn = f: x: trace (f x) x; /** Trace the supplied value and return it. # Inputs `x` : Value to trace and return # Type ``` traceVal :: a -> a ``` # Examples :::{.example} ## `lib.debug.traceVal` usage example ```nix traceVal 42 # trace: 42 => 42 ``` ::: */ traceVal = traceValFn id; /** `builtins.trace`, but the value is `builtins.deepSeq`ed first. # Inputs `x` : The value to trace `y` : The value to return # Type ``` traceSeq :: a -> b -> b ``` # Examples :::{.example} ## `lib.debug.traceSeq` usage example ```nix trace { a.b.c = 3; } null trace: { a = ; } => null traceSeq { a.b.c = 3; } null trace: { a = { b = { c = 3; }; }; } => null ``` ::: */ traceSeq = x: 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. # Inputs `depth` : 1\. Function argument `x` : 2\. Function argument `y` : 3\. Function argument # Type ``` traceSeqN :: Int -> a -> b -> b ``` # Examples :::{.example} ## `lib.debug.traceSeqN` usage example ```nix 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. # Inputs `f` : Function to apply `v` : Value to trace */ traceValSeqFn = f: v: traceValFn f (builtins.deepSeq v v); /** A combination of `traceVal` and `traceSeq`. # Inputs `v` : Value to trace */ traceValSeq = traceValSeqFn id; /** A combination of `traceVal` and `traceSeqN` that applies a provided function to the value to be traced. # Inputs `f` : Function to apply `depth` : 2\. Function argument `v` : Value to trace */ traceValSeqNFn = f: depth: v: traceSeqN depth (f v) v; /** A combination of `traceVal` and `traceSeqN`. # Inputs `depth` : 1\. Function argument `v` : Value to trace */ 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. # Inputs `depth` : 1\. Function argument `name` : 2\. Function argument `f` : 3\. Function argument `v` : 4\. Function argument # Examples :::{.example} ## `lib.debug.traceFnSeqN` usage example ```nix 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"];` # Inputs `tests` : Tests to run # Type ``` runTests :: { tests = [ String ]; ${testName} :: { expr :: a; expected :: a; }; } -> [ { name :: String; expected :: a; result :: a; } ] ``` # Examples :::{.example} ## `lib.debug.runTests` usage example ```nix runTests { testAndOk = { expr = lib.and true false; expected = false; }; testAndFail = { expr = lib.and true false; expected = true; }; } -> [ { name = "testAndFail"; expected = true; result = false; } ] ``` ::: */ runTests = 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`. # Inputs `expr` : 1\. Function argument # Examples :::{.example} ## `lib.debug.testAllTrue` usage example ```nix { testX = allTrue [ true ]; } ``` ::: */ testAllTrue = expr: { inherit expr; expected = map (x: true) expr; }; }