# Syntactic test suite coverage in Dr Racket

**URL:** <https://racket.discourse.group/t/syntactic-test-suite-coverage-in-dr-racket/1421>\
**Category:** General\
**Tags:** drracket\
**Created:** [October 30, 2022, 12:21am UTC](https://racket.discourse.group/t/syntactic-test-suite-coverage-in-dr-racket/1421 "2022-10-30T00:21:07Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![tehkonst](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/tehkonst/32/802_2.png) [@tehkonst](https://racket.discourse.group/u/tehkonst)\
**Post date:** [October 30, 2022, 12:21am UTC](https://racket.discourse.group/t/syntactic-test-suite-coverage-in-dr-racket/1421/1 "2022-10-30T00:21:07Z")

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Hi. I am trying to use drracket's syntactic test suite coverage.  
 ![image](https://global.discourse-cdn.com/free1/uploads/racket/original/1X/4280ac53caea6fce9c28ff6c2f4825fc4f5ca349.png)  
It always marks expressions in functions with optional arguments (see the screenshot).  
Can I make drracket test coverage to ignore these lines?

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**Author:** ![soegaard](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/soegaard/32/19_2.png) [@soegaard](https://racket.discourse.group/u/soegaard)\
**Post date:** [October 30, 2022, 10:31am UTC](https://racket.discourse.group/t/syntactic-test-suite-coverage-in-dr-racket/1421/2 "2022-10-30T10:31:32Z")

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This looks like a bug to me.

The expression `(func)` calls `func`without keyword arguments, so the default expressions 100, 200, and, `#t` are used. Therefore the tool shouldn't color them black.

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**Author:** ![jbclements](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/jbclements/32/11_2.png) [@jbclements](https://racket.discourse.group/u/jbclements)\
**Post date:** [November 8, 2022, 10:07pm UTC](https://racket.discourse.group/t/syntactic-test-suite-coverage-in-dr-racket/1421/3 "2022-11-08T22:07:51Z")

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It looks to me like this problem is specific to keyword arguments; when using other default arguments, the coloring appears correct. So, for example,

```scheme
#lang racket

(define (f [x 99])
  (+ x 1234))

(f)

```

results in full coverage.

File a bug report?

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**Author:** ![greghendershott](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/greghendershott/32/98_2.png) [@greghendershott](https://racket.discourse.group/u/greghendershott)\
**Post date:** [November 9, 2022, 2:55pm UTC](https://racket.discourse.group/t/syntactic-test-suite-coverage-in-dr-racket/1421/4 "2022-11-09T14:55:51Z")

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It also looks like it's limited to keyword argument functions that are _directly_ applied:

```scheme
#lang racket/base

(define (f [x 42])
  x)
(f)

(define (g #:x [x 42])
  x)
(g) ;<-- actually a macro invocation
(apply g '()) ;<-- actually runtime; now "42" is shown as used

```

The expansion of `f` is not much more than `case-lambda`.

The expansion of `g` is... fairly complicated. It looks like `g` is defined as a runtime function value -- but also an `g` is defined as a syntax transformer, for expansion time. Probably an optimization? Anyway in that case `42` seems truly not to be used, at runtime... or something like that?

> ****
>
> ```
> (module anonymous-module racket/base
> (#%module-begin
> (module configure-runtime '#%kernel
> (#%module-begin (#%require racket/runtime-config) (#%app configure (quote #f))))
> (define-values (f)
> (let-values (((f)
> (lambda (x1)
> (let-values (((x) (if (quote #f) (quote 42) x1))) (let-values () x)))))
> (case-lambda [() (#%app f (quote 42))] [(x1) (#%app f x1)])))
> (#%app call-with-values (lambda () (#%app f)) print-values)
> (define-syntaxes (g)
> (#%app
> make-keyword-syntax
> (lambda () (#%app values (quote-syntax g) (quote-syntax g4)))
> (quote 0)
> '()
> (quote #f)
> '()
> '((#:x x2:18 x3:19 #f 42))))
> (define-values:20 (g)
> (lambda (x2:18)
> (let-values:21 (((x) (if:22 (quote #f) (quote 42) x2:18))) (let-values:23 () x))))
> (define-values:24 (g:25)
> (lambda (given-kws given-args)
> (let-values:26 (((x3:19) (#%app:27 pair?:27 given-kws)))
> (let-values:28 (((x2:18) (if:27 x3:19 (#%app:27 car:27 given-args) (quote 42))))
> (#%app g x2:18)))))
> (define-values:29 (g4)
> (#%app
> make-optional-keyword-procedure
> (lambda (given-kws given-argc)
> (if:30 (#%app:31 =:31 given-argc (quote 2))
> (let-values:32 (((l125477:33) given-kws))
> (let-values:34 (((l125477:33)
> (if:33 (#%app:33 null?:33 l125477:33)
> l125477:33
> (if:33 (#%app:33 eq?:33 (#%app:33 car:33 l125477:33) '#:x)
> (#%app:33 cdr:33 l125477:33)
> l125477:33))))
> (#%app:35 null?:35 l125477:33)))
> (quote #f)))
> (case-lambda:36 [(given-kws given-args) (#%app:36 g:25 given-kws given-args)])
> null
> '(#:x)
> (case-lambda:37 [() (#%app:37 g:25 null null)])))
> (#%app:38
> call-with-values:38
> (lambda:38 ()
> (let-values:39 ()
> (if:40 (#%app:40 variable-reference-constant?:40 (#%variable-reference:40 g4:41))
> (#%app:40 g:42 (quote 42))
> (#%app:40 g4:41))))
> print-values:38)
> (#%app:43 call-with-values:43 (lambda:43 () (#%app:44 apply:45 g4:46 '())) print-values:43)))
> ```

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<div class="post-metadata">

**Author:** ![robby](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/robby/32/7_2.png) [@robby](https://racket.discourse.group/u/robby)\
**Post date:** [November 9, 2022, 3:20pm UTC](https://racket.discourse.group/t/syntactic-test-suite-coverage-in-dr-racket/1421/5 "2022-11-09T15:20:35Z")

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Not looking at the keyword implementation directly but just trying examples it also looks like an optimization to me. While this program shows the `42` as uncovered:

```scheme
#lang racket
(define (g #:x [x 3])
  x)
(g)

```

This program doesn't:

```scheme
#lang racket
(define (g #:x [x (+ 41 1)])
  x)
(g)

```

I wonder if one of the quoted `42`s in the fully expanded form needs to have the source location of the constant put onto it?

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<div class="post-metadata">

**Author:** ![greghendershott](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/greghendershott/32/98_2.png) [@greghendershott](https://racket.discourse.group/u/greghendershott)\
**Post date:** [November 9, 2022, 4:41pm UTC](https://racket.discourse.group/t/syntactic-test-suite-coverage-in-dr-racket/1421/6 "2022-11-09T16:41:56Z")

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Ah, that could be it. In the expansion of the direct `(g)`, here:

```scheme
(#%app:38
    call-with-values:38
    (lambda:38 ()
      (let-values:39 ()
        (if:40 (#%app:40 variable-reference-constant?:40 (#%variable-reference:40 g4:41))
          (#%app:40 g:42 (quote 42))
          (#%app:40 g4:41))))
    print-values:38)

```

The `42` has srcloc in private/kw.rkt, not in the user program.

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<div class="post-metadata">

**Author:** ![samth](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/samth/32/3_2.png) [@samth](https://racket.discourse.group/u/samth)\
**Post date:** [November 9, 2022, 6:09pm UTC](https://racket.discourse.group/t/syntactic-test-suite-coverage-in-dr-racket/1421/7 "2022-11-09T18:09:32Z")

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Right, what seems to happen is that the default value is stored in `make-keyword-syntax` as a value rather than a syntax object, and so there's no syntax location to re-use. I'm not sure how difficult it would be to change that to using a syntax object instead. The comment on line 1380 of racket/private/kw.rkt suggests that @mflatt thought about at least some aspects of this previously.

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<div class="post-metadata">

**Author:** ![mflatt](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/mflatt/32/6_2.png) [@mflatt](https://racket.discourse.group/u/mflatt)\
**Post date:** [November 10, 2022, 2:06am UTC](https://racket.discourse.group/t/syntactic-test-suite-coverage-in-dr-racket/1421/8 "2022-11-10T02:06:20Z")

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I've pushed a repair. Thanks, everyone, for reporting and tracking down the problem.