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Re: [PATCH] srfi-64: fix unused variable warnings

From: Maxime Devos
Subject: Re: [PATCH] srfi-64: fix unused variable warnings
Date: Thu, 01 Apr 2021 13:37:26 +0200
User-agent: Evolution 3.34.2

On Wed, 2021-03-31 at 23:11 -0700, Aleix Conchillo Flaqué wrote:
> * module/srfi/srfi-64/testing.scm: remove unused name variable and use
> let instead of let*.

I don't think this is the correct approach with respect to side effects.
For example, in:

>  (define (%test-comp2 comp x)
>      (syntax-case (list x (list (syntax quote) (%test-source-line2 x)) comp) 
> ()
>        (((mac tname expected expr) line comp)
>         (syntax
> -     (let* ((r (test-runner-get))
> -            (name tname))
> +     (let ((r (test-runner-get)))
>         (test-result-alist! r (cons (cons 'test-name tname) line))
>         (%test-comp2body r comp expected expr))))

I would keep the let* (but reverse the binding order), but change 'tname'
with 'name' in the call to 'test-result-alist!', such that 'test-X' macros
behave somewhat more like procedure calls (except for installing exeption
handlers and having access to the s-expression of the code that will be run,
of course).  It's largely a matter of taste, though.

In any case, it is good that 'tname' is now evaluated only once, as per
SRFI-64 (notice ***It is evaluated only once.*** (markup mine)):

 (test-assert [test-name] expression)

 This evaluates the expression. The test passes if the result is true;
 if the result is false, a test failure is reported. The test also fails
 if an exception is raised, assuming the implementation has a way to catch
 exceptions. How the failure is reported depends on the test runner environment.
 The test-name is a string that names the test case. (Though the test-name is
 a string literal in the examples, it is an expression. ***It is evaluated only 
 It is used when reporting errors, and also when skipping tests, as described 
 It is an error to invoke test-assert if there is no current test runner.

(My suggestion would be to also evaluate 'test-name' at least once, even if 
is no test runner, which seems a bit stricter than SRFI-64 demands, but seems 
a nice property to have and easy to achieve.)

As this patch does not ‘merely’ fix a warnings, but fixes a bug, could you 
the patch message accordingly?  Something like

  srfi-64: fix double evaluation of test-name.



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