State-of-the-art format string analysis

[ludo@gnu.org (Ludovic Courtès)]

Hello Guilers!

I’m proud to announce that Guile’s compiler now comes with
state-of-the-art format string static analysis™.

Initially, I thought ‘format’ was about ~A, ~S, ~f, and various obscure
flags that nobody really uses, until I found (thanks to our ‘format’
wizard—you know who you are) that (1) these obscure options are actually
used and useful, and (2) the ‘format’ language is on par with Brainfuck.

So, a few examples:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> ,o compile-options (#:warnings (unbound-variable arity-mismatch format))
scheme@(guile-user)> ,c (format 100 "~a")
<stdin>:9:3: warning: 100: wrong port argument
<stdin>:9:3: warning: "~a": wrong number of `format' arguments: expected 1, got 0
[...]

scheme@(guile-user)> ,c (format #f "~[chbouib~;~a~;~2*~a~]")
<stdin>:11:0: warning: "~[chbouib~;~a~;~2*~a~]": wrong number of `format' arguments: expected 1 to 4, got 0
[...]

scheme@(guile-user)> ,c (format #f "~A ~@{~S~}")
<stdin>:14:3: warning: "~A ~@{~S~}": wrong number of `format' arguments: expected at least 1, got 0
[...]

scheme@(guile-user)> ,c (format #f "~[")
<stdin>:16:0: warning: "~[": unterminated conditional
[...]
--8<---------------cut here---------------end--------------->8---

Comments welcome!

Ludo’.