Clean up trivial gcc -wextra warnings (#6254)

After verifying that they really were spurious, clean up the warnings
that gcc -wextra reports, except for LeaMDNS.

Upgrade GCC to gcc-7 for host builds

.travis.yml

@@ -6,6 +6,14 @@ git:
   depth: 1
   submodules: false
 
+addons:
+  apt:
+    sources:
+      - ubuntu-toolchain-r-test
+    packages:
+      - g++-7
+      - gcc-7
+
 before_install:
   - git submodule update --init  # no recursive update
 
@@ -80,6 +88,7 @@ jobs:
       stage: build
       script: $TRAVIS_BUILD_DIR/tests/ci/host_test.sh
       install: sudo apt-get install valgrind lcov
+      env: CC=gcc-7 CXX=g++-7
 
     - name: "Docs"
       stage: build
@@ -96,6 +105,7 @@ jobs:
     - name: "Mock trivial test"
       stage: build
       script: $TRAVIS_BUILD_DIR/tests/buildm.sh
+      env: CC=gcc-7 CXX=g++-7
 
     - name: "Boards"
       stage: build

cores/esp8266/libb64/cdecode.cpp

@@ -43,6 +43,7 @@ static int base64_decode_block_signed(const int8_t* code_in, const int length_in
           fragment = (int8_t)base64_decode_value_signed(*codechar++);
         } while (fragment < 0);
         *plainchar    = (fragment & 0x03f) << 2;
+        // falls through
       case step_b:
         do {
           if (codechar == code_in+length_in){
@@ -54,6 +55,7 @@ static int base64_decode_block_signed(const int8_t* code_in, const int length_in
         } while (fragment < 0);
         *plainchar++ |= (fragment & 0x030) >> 4;
         *plainchar    = (fragment & 0x00f) << 4;
+        // falls through
       case step_c:
         do {
           if (codechar == code_in+length_in){
@@ -65,6 +67,7 @@ static int base64_decode_block_signed(const int8_t* code_in, const int length_in
         } while (fragment < 0);
         *plainchar++ |= (fragment & 0x03c) >> 2;
         *plainchar    = (fragment & 0x003) << 6;
+        // falls through
       case step_d:
         do {
           if (codechar == code_in+length_in){

cores/esp8266/libb64/cencode.cpp

@@ -50,6 +50,7 @@ int base64_encode_block(const char* plaintext_in, int length_in, char* code_out,
       result = (fragment & 0x0fc) >> 2;
       *codechar++ = base64_encode_value(result);
       result = (fragment & 0x003) << 4;
+      // falls through
   case step_B:
       if (plainchar == plaintextend){
         state_in->result = result;
@@ -60,6 +61,7 @@ int base64_encode_block(const char* plaintext_in, int length_in, char* code_out,
       result |= (fragment & 0x0f0) >> 4;
       *codechar++ = base64_encode_value(result);
       result = (fragment & 0x00f) << 2;
+      // falls through
   case step_C:
       if (plainchar == plaintextend){
         state_in->result = result;

libraries/ESP8266AVRISP/src/ESP8266AVRISP.cpp

@@ -107,10 +107,9 @@ AVRISPState_t ESP8266AVRISP::serve() {
         case AVRISP_STATE_IDLE:
             // should not be called when idle, error?
             break;
-        case AVRISP_STATE_PENDING: {
+        case AVRISP_STATE_PENDING:
             _state = AVRISP_STATE_ACTIVE;
-        // fallthrough
+            // falls through
-        }
         case AVRISP_STATE_ACTIVE: {
             while (_client.available()) {
                 avrisp();

tests/host/Makefile

@@ -153,6 +153,7 @@ FLAGS += -DLWIP_IPV6=0
 FLAGS += -DHOST_MOCK=1
 FLAGS += -DNONOSDK221=1
 FLAGS += $(MKFLAGS)
+FLAGS += -Wimplicit-fallthrough=2 # allow "// fall through" comments to stop spurious warnings
 CXXFLAGS += -std=c++11 -fno-rtti $(FLAGS) -funsigned-char
 CFLAGS += -std=c99 $(FLAGS) -funsigned-char
 LDFLAGS += -coverage $(OPTZ) -g $(M32)

tests/host/common/UdpContextSocket.cpp

@@ -155,6 +155,7 @@ size_t mockUDPFillInBuf (int sock, char* ccinbuf, size_t& ccinbufsize, uint8_t&
 size_t mockUDPPeekBytes (int sock, char* dst, size_t usersize, int timeout_ms, char* ccinbuf, size_t& ccinbufsize)
 {
 	(void) sock;
+	(void) timeout_ms;  
 	if (usersize > CCBUFSIZE)
 		fprintf(stderr, MOCK "CCBUFSIZE(%d) should be increased by %zd bytes (-> %zd)\n", CCBUFSIZE, usersize - CCBUFSIZE, usersize);
 

tests/host/common/include/ClientContext.h

@@ -258,6 +258,9 @@ public:
 
     void keepAlive (uint16_t idle_sec = TCP_DEFAULT_KEEPALIVE_IDLE_SEC, uint16_t intv_sec = TCP_DEFAULT_KEEPALIVE_INTERVAL_SEC, uint8_t count = TCP_DEFAULT_KEEPALIVE_COUNT)
     {
+        (void) idle_sec;
+        (void) intv_sec;
+        (void) count;
         mockverbose("TODO ClientContext::keepAlive()\n");
     }