[Bug c/108701] New: Incorrect -Wmisleading-indentation

[Bug c/108701] New: Incorrect -Wmisleading-indentation

[apjo at tuta dot io]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108701

            Bug ID: 108701
           Summary: Incorrect -Wmisleading-indentation
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: apjo at tuta dot io
  Target Milestone: ---

Godbolt link (GCC 12.2.0) demonstrating the occurance of the issue :
https://godbolt.org/z/Gx4677oPj

Godbolt link of Clang 15.0.0 with the same input & options not having the
incorrect warning : https://godbolt.org/z/rWrnGnj7d

This is self-explanatory and completely reproducible. Do let me know if there's
any more assistance I can offer.

[Bug c/108701] Incorrect -Wmisleading-indentation

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108701

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Created attachment 54421
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54421&action=edit
testcase

[Bug c/108701] Incorrect -Wmisleading-indentation

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108701

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2023-02-07
     Ever confirmed|0                           |1

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
-ftabstop=4 fixes the warning.
Looks like godbolt is using 4 spaces/tab in their editor but GCC defaults to 8
spaces per tab.

I suspect you need to supply -ftabstop=4 to override GCC's defaults if you are
using 4space/tabs.

[Bug c/108701] Incorrect -Wmisleading-indentation

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108701

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|---                         |INVALID

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The documentation is clear too:
https://gcc.gnu.org/onlinedocs/gcc-12.2.0/gcc/Warning-Options.html#index-Wmisleading-indentation

In the case of mixed tabs and spaces, the warning uses the -ftabstop= option to
determine if the statements line up (defaulting to 8).

[Bug c/108701] Incorrect -Wmisleading-indentation

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108701

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Also once you change godbolt to be 8 spaces/tab, it becomes obvious the warning
is correct for the default.

[Bug c/108701] Incorrect -Wmisleading-indentation

[apjo at tuta dot io]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108701

apjo at tuta dot io <apjo at tuta dot io> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|INVALID                     |FIXED

--- Comment #5 from apjo at tuta dot io <apjo at tuta dot io> ---
(In reply to Andrew Pinski from comment #2)
> -ftabstop=4 fixes the warning.
> Looks like godbolt is using 4 spaces/tab in their editor but GCC defaults to
> 8 spaces per tab.
> 
> I suspect you need to supply -ftabstop=4 to override GCC's defaults if you
> are using 4space/tabs.

Interesting. I only ever use \t tabs for indentations and 1 \t == 8 spaces on
my editors, but Godbolt's default behavior is this weird thing I guess.

[Bug c/108701] Incorrect -Wmisleading-indentation

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108701

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|FIXED                       |INVALID

[Bug c/108701] Incorrect -Wmisleading-indentation

[apjo at tuta dot io]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108701

apjo at tuta dot io <apjo at tuta dot io> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|INVALID                     |FIXED

--- Comment #6 from apjo at tuta dot io <apjo at tuta dot io> ---
Also, thanks Andrew for the prompt reply and solution.

I had a couple follow up questions:
- How is clang getting this right? I guess it defaults to 4 space tab
(heretics!).
- So is this 'basically not a bug'?

[Bug c/108701] Incorrect -Wmisleading-indentation

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108701

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|FIXED                       |INVALID

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I don't know how clang is not warning.  Maybe they don't take into account
spaces vs tabs ...

[Bug c/108701] Incorrect -Wmisleading-indentation

[apjo at tuta dot io]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108701

apjo at tuta dot io <apjo at tuta dot io> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|INVALID                     |---
             Status|RESOLVED                    |REOPENED

--- Comment #8 from apjo at tuta dot io <apjo at tuta dot io> ---
Clang can do it right so GCC should be able to too.

[Bug c/108701] Incorrect -Wmisleading-indentation

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108701

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|---                         |INVALID

--- Comment #9 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
clang is not even warning for -Wmisleading-indentation so it is not doing it
right or wrong there ...

[Bug c/108701] Incorrect -Wmisleading-indentation

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108701

--- Comment #10 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
That is clang does not warn about this case here (changed all tabs to spaces to
indepdent of -ftabstop option):
```
int randBytesGet()
{
        int t;   

        while (true) {

            if (true)
                return 0;
                #if 0
                    int random = rand();
                #endif
                t = 0;
        }
        return t;
}
```
GCC correctly warns about the `t = 0;` statement:
```
<source>: In function 'int randBytesGet()':
<source>:8:13: warning: this 'if' clause does not guard...
[-Wmisleading-indentation]
    8 |             if (true)
      |             ^~
<source>:13:17: note: ...this statement, but the latter is misleadingly
indented as if it were guarded by the 'if'
   13 |                 t = 0;
      |                 ^
```

[Bug c/108701] Incorrect -Wmisleading-indentation

[apjo at tuta dot io]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108701

--- Comment #11 from apjo at tuta dot io <apjo at tuta dot io> ---
(In reply to Andrew Pinski from comment #10)

Okay now that looks like a clang bug. Clang is supposed to diagnose misleading
indentation like that (see: https://godbolt.org/z/1fv4rEseo).