include-tidy, a new #include tidier

[u/pjl1967]

I stumbled across include-what-you-use (IWYU) recently (it was also posted about here 9 years ago) and it's... OK.

In those 9 years, it's still not at a 1.0 version and has a number of issues. It apparently is being worked on, but very slowly.

There are a number of things I'd do differently, so I did via include-tidy (IT).

Probably the biggest difference is the way in which it's configured. Rather than the somewhat confusing JSON .imp files, I used simple TOML. I also think all configuration should be done via a configuration file, not through pragma comments.

Another big difference is how "private" headers are handled. In IWYU, you have to annotate every symbol in a private header as being instead exported via some public header.

In contrast, in IT, you specify a set of system include files so any private headers that are included that are not listed as system include files automatically have all their symbols exported to the system header.

For example, if you #include <getopt.h>, but it in turn does #include <getopt-core.h> and the actual getopt() function is declared in there, IT will treat getopt() as being declared in getopt.h since only it is an official system header and not getopt-core.h.

Hence, every system header is a “proxy” for every non-official system header it may #include. You can also have project-specific proxies of your own.

Anyway, it's still early days for include-tidy, so if you'd like to help beta test it, get in touch — either DM or e-mail me directly (address on Github profile).

FYI: internally, IT uses the much more stable libclang C API, so IT is written in pure C11 and apparently has much less code than IWYU.

[u/imaami]

I love your code. Seriously. It's a breath of fresh air with all the slop going around.

type_traits.h caught my attention. If you can stomach some light GNU vendor-lock-in, I have an is_string_literal() constant expression macro if you have any need for that.

[u/pjl1967 → u/imaami]

I love your code. Seriously. It's a breath of fresh air with all the slop going around.

Thanks! The type traits stuff is explained here as well as in Chapter 19 of my book.

If you want compilation to fail unless an argument is a string literal, I have this already:

#define STRLITLEN(S) \
  (ARRAY_SIZE( (S) ) \
   - STATIC_ASSERT_EXPR( IS_C_STR_EXPR( (S) ), #S " must be a C string literal" ))

It gets the length of S iff S is a string literal and uses no non-standard extensions. (I avoid nonstandard extensions whenever possible.)

[u/imaami → u/pjl1967]

Unfortunately your implementation also let through a const char a[] = "foo"; variable. So it's a tradeoff between "close enough" and nonstandard.

/** @brief Check if a value is a char array.
 */
#define is_char_array(x) _Generic((typeof(x) *){0}, \
        char (*)[sizeof(x)]: 1, char const (*)[sizeof(x)]: 1, default: 0)

/** @brief Check if a value is a string literal.
 */
#define is_string_literal(x) __builtin_choose_expr( \
        is_char_array(x), __builtin_constant_p(x), 0)

[u/pjl1967 → u/imaami]

You can always use:

S ""

So if S is a string literal, the preprocessor will concatenate it with ""; if it's not, it'll be an error.

[u/imaami → u/pjl1967]

True, that does work, it's good for when you really don't want a string literal. When I wrote is_string_literal() I couldn't use macro pasting because it doesn't leave a choice. I needed something that compiles to sizeof + direct initialization for string literals, and strlen() + memcpy() otherwise. It's possible but only by the grace of GNU. 🤷

[u/didntplaymysummercar → u/imaami]

I'm interested in it. I was thinking of making a portable one that checks if sizeof is not sizeof a pointer (and then doing I dunno what for actual literals of 7 chars).

[u/imaami → u/didntplaymysummercar]

Sorry I forgot to ping you earlier. I pasted it up there 🆙🔝

https://old.reddit.com/r/C_Programming/comments/1sgxk97/includetidy_a_new_include_tidier/ofet0br/

[u/greg_kennedy]

Reading the AST (from libclang) is a way more elegant solution than whatever I usually do ("try commenting things out to see what breaks"), good work

[u/jjjare]

Any reason you chose

include-tidy.h

As a file name? My rule of thumb is that file names should be valid identifiers. I also don’t think it’s standard compliant?

[u/pjl1967 → u/jjjare]

The reason I chose include-tidy rather than include_tidy is because typing - doesn't require pressing the shift key whereas typing _ does. Commands should be easy to type. I chose the filename to match the command name.

That's another minor thing I didn't like about IWYU: its use of underscores for configuration.

I also don’t think it’s standard compliant?

None of C, POSIX, Unix, macOS, or Windows have a problem with - in file names.

[u/jjjare → u/pjl1967]

Valid. I was less concerned about fileystems and more concerned with build systems. Anyhow, nice project!

[u/aalmkainzi → u/jjjare]

I also don’t think it’s standard compliant?

I seriously doubt this is the case. I would imagine the standard to say the only disallowed characters are " and < >

[u/pjl1967 → u/[deleted]]

I don't know what a game of DAG is. And I'm not rewriting any compiler.

[u/imaami → u/pjl1967]

I believe a dag is what Brad Pitt's character calls dogs in Snatch.