[3.6] bpo-30923: Silence fall-through warnings included in -Wextra since gcc-7.0 (#3518)

* bpo-30923: Disable warning that has been part of -Wextra since gcc-7.0. (#3142)

(cherry picked from commit d73a960c575207539c3f9765cff26d4fff400b45)

* bpo-30923: Silence fall-through warnings included in -Wextra since gcc-7.0. (#3157)

(cherry picked from commit f432a3234f9f2ee09bd40be03e06bf72865ee375)

* bpo-31275: Small refactoring to silence a fall-through warning. (#3206)

(cherry picked from commit 138753c1b96b5e06a5c5d409fa4cae5e2fe1108b)

3 files changed, 9 insertions, 9 deletions

diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index 2c01e37..1ced630 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -3675,7 +3675,7 @@ _build_callargs(PyCFuncPtrObject *self, PyObject *argtypes,
         case (PARAMFLAG_FIN | PARAMFLAG_FOUT):
             *pinoutmask |= (1 << i); /* mark as inout arg */
             (*pnumretvals)++;
-            /* fall through to PARAMFLAG_FIN... */
+            /* fall through */
         case 0:
         case PARAMFLAG_FIN:
             /* 'in' parameter.  Copy it from inargs. */
diff --git a/Modules/_decimal/libmpdec/io.c b/Modules/_decimal/libmpdec/io.c
index 3aadfb0..f45e558 100644
--- a/Modules/_decimal/libmpdec/io.c
+++ b/Modules/_decimal/libmpdec/io.c
@@ -45,6 +45,12 @@
    PEP-3101 formatting for numeric types. */
 
 
+/* Disable warning that is part of -Wextra since gcc 7.0. */
+#if defined(__GNUC__) && !defined(__INTEL_COMPILER) && __GNUC__ >= 7
+  #pragma GCC diagnostic ignored "-Wimplicit-fallthrough"
+#endif
+
+
 /*
  * Work around the behavior of tolower() and strcasecmp() in certain
  * locales. For example, in tr_TR.utf8:
diff --git a/Modules/cjkcodecs/_codecs_iso2022.c b/Modules/cjkcodecs/_codecs_iso2022.c
index 1ce4218..7394cf6 100644
--- a/Modules/cjkcodecs/_codecs_iso2022.c
+++ b/Modules/cjkcodecs/_codecs_iso2022.c
@@ -807,15 +807,9 @@ jisx0213_encoder(const Py_UCS4 *data, Py_ssize_t *length, void *config)
     case 2: /* second character of unicode pair */
         coded = find_pairencmap((ucs2_t)data[0], (ucs2_t)data[1],
                                 jisx0213_pair_encmap, JISX0213_ENCPAIRS);
-        if (coded == DBCINV) {
-            *length = 1;
-            coded = find_pairencmap((ucs2_t)data[0], 0,
-                      jisx0213_pair_encmap, JISX0213_ENCPAIRS);
-            if (coded == DBCINV)
-                return MAP_UNMAPPABLE;
-        }
-        else
+        if (coded != DBCINV)
             return coded;
+        /* fall through */
 
     case -1: /* flush unterminated */
         *length = 1;