Make SPIFFS and LittleFS stay out of link when not needed (#6699)

* define two weak functions defaulting to no-op
redefine them to do something useful when either spiffs or littlefs are used

* noop

* single entry point for closing FSes

* rename functions, override when instanciated, add link to explanation

* spiffs: call end on destructor

cores/esp8266/FS.h

@@ -245,6 +245,13 @@ protected:
 
 } // namespace fs
 
+extern "C"
+{
+void close_all_fs(void);
+void littlefs_request_end(void);
+void spiffs_request_end(void);
+}
+
 #ifndef FS_NO_GLOBALS
 using fs::FS;
 using fs::File;

cores/esp8266/FSnoop.cpp

@@ -0,0 +1,33 @@
+/*
+ *  no-op implementations
+ *  used/linked when no strong implementation already exists elsewhere
+ */
+
+#include <FS.h>
+
+extern "C"
+{
+
+void close_all_fs(void)
+{
+    littlefs_request_end();
+    spiffs_request_end();
+}
+
+// default weak definitions
+// they are overriden in their respective real implementation
+// hint: https://github.com/esp8266/Arduino/pull/6699#issuecomment-549085382
+
+void littlefs_request_end(void) __attribute__((weak));
+void littlefs_request_end(void)
+{
+    //ets_printf("debug: noop: littlefs_request_end\n");
+}
+
+void spiffs_request_end(void) __attribute__((weak));
+void spiffs_request_end(void)
+{
+    //ets_printf("debug: noop: spiffs_request_end\n");
+}
+
+}

cores/esp8266/spiffs_api.cpp

@@ -141,6 +141,14 @@ FS SPIFFS = FS(FSImplPtr(new spiffs_impl::SPIFFSImpl(
                              FS_PHYS_PAGE,
                              FS_PHYS_BLOCK,
                              SPIFFS_MAX_OPEN_FILES)));
+
+extern "C" void spiffs_request_end(void)
+{
+    // override default weak function
+    //ets_printf("debug: not weak spiffs end\n");
+    SPIFFS.end();
+}
+
 #endif // ARDUINO
 #endif // !CORE_MOCK
 

cores/esp8266/spiffs_api.h

@@ -80,6 +80,11 @@ public:
         memset(&_fs, 0, sizeof(_fs));
     }
 
+    ~SPIFFSImpl()
+    {
+        end();
+    }
+
     FileImplPtr open(const char* path, OpenMode openMode, AccessMode accessMode) override;
     bool exists(const char* path) override;
     DirImplPtr openDir(const char* path) override;