[RFC PATCH v2 78/78] meson.build: increase -Wimplicit-fallthrough to 5

[Emmanouil Pitsidianakis]

Make GCC's implicit fall-through static analysis stricter by requiring
the use of the fallthrough attribute statement instead of comments.

This makes the QEMU code style more consistent.

Signed-off-by: Emmanouil Pitsidianakis <manos.pitsidianakis@linaro.org>
---
 docs/devel/style.rst | 23 +++++++++++++++++++++++
 meson.build          |  2 +-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/docs/devel/style.rst b/docs/devel/style.rst
index 2f68b50079..f473dd24e9 100644
--- a/docs/devel/style.rst
+++ b/docs/devel/style.rst
@@ -612,28 +612,51 @@ While this generally results in simpler, less leak-prone 
code, there
 are still some caveats to beware of
 
 * Variables declared with g_auto* MUST always be initialized,
   otherwise the cleanup function will use uninitialized stack memory
 
 * If a variable declared with g_auto* holds a value which must
   live beyond the life of the function, that value must be saved
   and the original variable NULL'd out. This can be simpler using
   g_steal_pointer
 
 
 .. code-block:: c
 
     char *somefunc(void)
     {
         g_autofree char *foo = g_strdup_printf("foo%", "wibble");
         g_autoptr (GList) bar = .....
 
         if (eek) {
            return NULL;
         }
 
         return g_steal_pointer(&foo);
     }
 
+Implicit switch case fall-through
+=================================
+
+The C language allows switch cases to "fall-through" when a "break" statement
+is missing at the end of a case. This, however, introduces ambiguity in the
+code, as it's not always clear if the missing break is intentional or a bug.
+
+As this behaviour allows for bugs we do not allow "implicit fall-through".
+
+In order to identify intentional fall-through cases, we have adopted a
+pseudo-keyword macro 'fallthrough' which expands to gcc's extension
+__attribute__((__fallthrough__)).  `Statement Attributes
+<https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html>`_
+
+All switch/case blocks must end in one of:
+
+.. code-block:: c
+
+         break;
+         fallthrough;
+         continue;
+         goto <label>;
+         return [expression];
 
 QEMU Specific Idioms
 ********************
diff --git a/meson.build b/meson.build
index 79aef19bdc..e8805f0e0c 100644
--- a/meson.build
+++ b/meson.build
@@ -438,28 +438,28 @@ add_global_link_arguments(qemu_ldflags, native: false, 
language: all_languages)
 warn_flags = [
   '-Wundef',
   '-Wwrite-strings',
   '-Wmissing-prototypes',
   '-Wstrict-prototypes',
   '-Wredundant-decls',
   '-Wold-style-declaration',
   '-Wold-style-definition',
   '-Wtype-limits',
   '-Wformat-security',
   '-Wformat-y2k',
   '-Winit-self',
   '-Wignored-qualifiers',
   '-Wempty-body',
   '-Wnested-externs',
   '-Wendif-labels',
   '-Wexpansion-to-defined',
-  '-Wimplicit-fallthrough=2',
+  '-Wimplicit-fallthrough=5',
   '-Wmissing-format-attribute',
   '-Wno-initializer-overrides',
   '-Wno-missing-include-dirs',
   '-Wno-shift-negative-value',
   '-Wno-string-plus-int',
   '-Wno-typedef-redefinition',
   '-Wno-tautological-type-limit-compare',
   '-Wno-psabi',
   '-Wno-gnu-variable-sized-type-not-at-end',
 ]
-- 
2.39.2