[PATCH 4/4] Add -Wmisleading-indentation to -Wall

[David Malcolm <dmalcolm at redhat dot com>]

Our documentation describes -Wall as enabling "all the warnings about
constructions that some users consider questionable, and that are easy to avoid
(or modify to prevent the warning), even in conjunction with macros."

I believe that -Wmisleading-indentation meets these criteria, and is
likely to be of benefit to users who may not read release notes; it
warns for indentation that's misleading, but not for indentation
that's merely bad: the former are places where a user will likely
want to fix the code.

The fix is usually easy and obvious: fix the misleadingly-indented
code.  If that isn't an option for some reason, pragmas can be used to
turn off the warning for a particular fragment of code:

  #pragma GCC diagnostic push
  #pragma GCC diagnostic ignored "-Wmisleading-indentation"
    if (flag)
      x = 3;
      y = 2;
  #pragma GCC diagnostic pop

-Wmisleading-indentation has been tested with a variety of indentation
styles (see gcc/testsuite/c-c++-common/Wmisleading-indentation.c)
and on a variety of real-world projects.  For example, in:
  https://www.mail-archive.com/gcc-patches@gcc.gnu.org/msg119790.html
Patrick reports:
"Tested by building the linux, git, vim, sqlite and gdb-binutils sources
 with -Wmisleading-indentation."

With the tweak earlier in this kit I believe we now have a good
enough signal:noise ratio for this warning to be widely used; hence this
patch adds the warning to -Wall.

Bootstrapped&regrtested with x86_64-pc-linux-gnu.

OK for trunk?

gcc/c-family/ChangeLog:
	* c.opt (Wmisleading-indentation): Add to -Wall for C and C++.

gcc/ChangeLog:
	* doc/invoke.texi (-Wall): Add -Wmisleading-indentation to the
	list.
	(-Wmisleading-indentation): Update documentation to reflect
	being enabled by -Wall in C/C++.
---
 gcc/c-family/c.opt  | 2 +-
 gcc/doc/invoke.texi | 5 +++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index e573254..d603511 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -562,7 +562,7 @@ C ObjC C++ ObjC++ Var(warn_memset_transposed_args) Warning LangEnabledBy(C ObjC
 Warn about suspicious calls to memset where the third argument is constant literal zero and the second is not.
 
 Wmisleading-indentation
-C C++ Common Var(warn_misleading_indentation) Warning
+C C++ Common Var(warn_misleading_indentation) Warning LangEnabledBy(C C++,Wall)
 Warn when the indentation of the code does not reflect the block structure.
 
 Wmissing-braces
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 5665315..abbbe5f 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -3531,6 +3531,7 @@ Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
 -Wformat   @gol
 -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)}  @gol
 -Wmaybe-uninitialized @gol
+-Wmisleading-indentation @r{(only for C/C++)} @gol
 -Wmissing-braces @r{(only for C/ObjC)} @gol
 -Wnonnull  @gol
 -Wopenmp-simd @gol
@@ -3876,8 +3877,6 @@ Specifically, a warning is issued for @code{if}, @code{else}, @code{while}, and
 @code{for} clauses with a guarded statement that does not use braces,
 followed by an unguarded statement with the same indentation.
 
-This warning is disabled by default.
-
 In the following example, the call to ``bar'' is misleadingly indented as
 if it were guarded by the ``if'' conditional.
 
@@ -3907,6 +3906,8 @@ The warning is not issued after a @code{#line} directive, since this
 typically indicates autogenerated code, and no assumptions can be made
 about the layout of the file that the directive references.
 
+This warning is enabled by @option{-Wall} in C and C++.
+
 @item -Wmissing-braces
 @opindex Wmissing-braces
 @opindex Wno-missing-braces
-- 
1.8.5.3