use attributes to indicate switch fall through instead of commentsvince/fallthrough

16 files changed, 85 insertions, 50 deletions

diff --git a/Makefile b/Makefile
index 5cb55561f..18665ed3d 100644
--- a/Makefile
+++ b/Makefile
@@ -90,13 +90,13 @@ ifeq ($(call cc_ver_ge,4,6),1)
 endif
 
 ifeq ($(TOOLCHAIN),gcc)
-  # Implicit fallthrough warnings suppressed by comment
+  # Implicit fallthrough warnings
   ifeq ($(call cc_ver_ge,7,1),1)
-    COMMON_WARNFLAGS += -Wimplicit-fallthrough=3
+    COMMON_WARNFLAGS += -Wimplicit-fallthrough=5
   endif
 else
-  # clang uses [[clang::fallthrough]] to annotate fallthrough instead of comments
-  COMMON_WARNFLAGS += -Wno-implicit-fallthrough
+  # non gcc has different warning syntax
+  COMMON_WARNFLAGS += -Wimplicit-fallthrough
 endif
 
 # deal with chaging warning flags for different platforms
diff --git a/content/handlers/css/hints.c b/content/handlers/css/hints.c
index 145cf8185..0f246a64c 100644
--- a/content/handlers/css/hints.c
+++ b/content/handlers/css/hints.c
@@ -1650,22 +1650,22 @@ css_error node_presentational_hint(void *pw, void *node,
 		css_hint_width(pw, node);
 		css_hint_table_cell_border_padding(pw, node);
 		css_hint_white_space_nowrap(pw, node);
-		/* fall through */
+		fallthrough;
 	case DOM_HTML_ELEMENT_TYPE_TR:
 		css_hint_height(pw, node);
-		/* fall through */
+		fallthrough;
 	case DOM_HTML_ELEMENT_TYPE_THEAD:
 	case DOM_HTML_ELEMENT_TYPE_TBODY:
 	case DOM_HTML_ELEMENT_TYPE_TFOOT:
 		css_hint_text_align_special(pw, node);
-		/* fall through */
+		fallthrough;
 	case DOM_HTML_ELEMENT_TYPE_COL:
 		css_hint_vertical_align_table_cells(pw, node);
 		break;
 	case DOM_HTML_ELEMENT_TYPE_APPLET:
 	case DOM_HTML_ELEMENT_TYPE_IMG:
 		css_hint_margin_hspace_vspace(pw, node);
-		/* fall through */
+		fallthrough;
 	case DOM_HTML_ELEMENT_TYPE_EMBED:
 	case DOM_HTML_ELEMENT_TYPE_IFRAME:
 	case DOM_HTML_ELEMENT_TYPE_OBJECT:
@@ -1688,7 +1688,7 @@ css_error node_presentational_hint(void *pw, void *node,
 		break;
 	case DOM_HTML_ELEMENT_TYPE_CAPTION:
 		css_hint_caption_side(pw, node);
-		/* fall through */
+		fallthrough;
 	case DOM_HTML_ELEMENT_TYPE_DIV:
 		css_hint_text_align_special(pw, node);
 		break;
diff --git a/content/handlers/html/box_inspect.c b/content/handlers/html/box_inspect.c
index 181f58cf8..6591b6446 100644
--- a/content/handlers/html/box_inspect.c
+++ b/content/handlers/html/box_inspect.c
@@ -25,6 +25,7 @@
 #include <stdio.h>
 #include <dom/dom.h>
 
+#include "utils/utils.h"
 #include "utils/nsurl.h"
 #include "utils/errors.h"
 #include "netsurf/types.h"
@@ -212,7 +213,7 @@ box_move_xy(struct box *b, enum box_walk_dir dir, int *x, int *y)
 			rb = b;
 			break;
 		}
-		/* fall through */
+		fallthrough;
 
 	case BOX_WALK_NEXT_SIBLING:
 		do {
diff --git a/content/handlers/html/dom_event.c b/content/handlers/html/dom_event.c
index d389a21b4..d42882515 100644
--- a/content/handlers/html/dom_event.c
+++ b/content/handlers/html/dom_event.c
@@ -25,6 +25,7 @@
 #include <string.h>
 
 #include "utils/config.h"
+#include "utils/utils.h"
 #include "utils/corestrings.h"
 #include "utils/nsoption.h"
 #include "utils/log.h"
@@ -691,6 +692,7 @@ dom_default_action_DOMNodeInsertedIntoDocument_cb(struct dom_event *evt,
 			switch (tag_type) {
 			case DOM_HTML_ELEMENT_TYPE_SCRIPT:
 				dom_SCRIPT_showed_up(htmlc, (dom_html_script_element *) node);
+				fallthrough;
 			default:
 				break;
 			}
@@ -740,6 +742,7 @@ dom_default_action_DOMSubtreeModified_cb(struct dom_event *evt, void *pw)
 			case DOM_HTML_ELEMENT_TYPE_TEXTAREA:
 			case DOM_HTML_ELEMENT_TYPE_INPUT:
 				html_texty_element_update(htmlc, (dom_node *)node);
+				fallthrough;
 			default:
 				break;
 			}
diff --git a/content/handlers/html/interaction.c b/content/handlers/html/interaction.c
index 9e359c98f..0a843e026 100644
--- a/content/handlers/html/interaction.c
+++ b/content/handlers/html/interaction.c
@@ -899,7 +899,7 @@ gadget_mouse_action(html_content *html,
 			}
 			free(oldcoords);
 		}
-		/* Fall through */
+		fallthrough;
 
 	case GADGET_SUBMIT:
 		if (mas->gadget.control->form) {
@@ -1669,7 +1669,7 @@ void html_set_drag_type(html_content *html, html_drag_type drag_type,
 
 	case HTML_DRAG_SELECTION:
 		assert(drag_owner.no_owner == true);
-		/* Fall through */
+		fallthrough;
 	case HTML_DRAG_TEXTAREA_SELECTION:
 	case HTML_DRAG_CONTENT_SELECTION:
 		msg_data.drag.type = CONTENT_DRAG_SELECTION;
@@ -1800,7 +1800,7 @@ void html_set_selection(html_content *html, html_selection_type selection_type,
 		break;
 	case HTML_SELECTION_SELF:
 		assert(selection_owner.none == false);
-		/* fall through */
+		fallthrough;
 	case HTML_SELECTION_TEXTAREA:
 	case HTML_SELECTION_CONTENT:
 		msg_data.selection.selection = true;
diff --git a/content/handlers/html/layout_flex.c b/content/handlers/html/layout_flex.c
index 61adcaa6c..bde3c5bd1 100644
--- a/content/handlers/html/layout_flex.c
+++ b/content/handlers/html/layout_flex.c
@@ -960,7 +960,6 @@ static void layout_flex__place_line_items_cross(struct flex_ctx *ctx,
 
 		switch (lh__box_align_self(ctx->flex, b)) {
 		default:
-			/* Fall through. */
 		case CSS_ALIGN_SELF_STRETCH:
 			if (lh__box_size_cross_is_auto(ctx->horizontal, b)) {
 				*box_size_cross += cross_free_space;
@@ -970,7 +969,7 @@ static void layout_flex__place_line_items_cross(struct flex_ctx *ctx,
 					return;
 				}
 			}
-			/* Fall through. */
+			fallthrough;
 		case CSS_ALIGN_SELF_FLEX_START:
 			*box_pos_cross = ctx->flex->padding[cross_start] +
 					line->pos +
@@ -986,7 +985,6 @@ static void layout_flex__place_line_items_cross(struct flex_ctx *ctx,
 			break;
 
 		case CSS_ALIGN_SELF_BASELINE:
-			/* Fall through. */
 		case CSS_ALIGN_SELF_CENTER:
 			*box_pos_cross = ctx->flex->padding[cross_start] +
 					line->pos + cross_free_space / 2 +
diff --git a/content/handlers/html/redraw_border.c b/content/handlers/html/redraw_border.c
index 39ed432cd..3a1f6f308 100644
--- a/content/handlers/html/redraw_border.c
+++ b/content/handlers/html/redraw_border.c
@@ -25,6 +25,7 @@
 #include <stdbool.h>
 #include <stdlib.h>
 
+#include "utils/utils.h"
 #include "utils/log.h"
 #include "netsurf/plotters.h"
 #include "netsurf/css.h"
@@ -121,7 +122,7 @@ html_redraw_border_plot(const int side,
 	switch (style) {
 	case CSS_BORDER_STYLE_DOTTED:
 		plot_style_bdr.stroke_type = PLOT_OP_TYPE_DOT;
-		/* fall through */
+		fallthrough;
 	case CSS_BORDER_STYLE_DASHED:
 		rect.x0 = (p[0] + p[2]) / 2;
 		rect.y0 = (p[1] + p[3]) / 2;
@@ -131,7 +132,7 @@ html_redraw_border_plot(const int side,
 		break;
 
 	case CSS_BORDER_STYLE_SOLID:
-		/* fall through to default */
+		/* solid is the default */
 	default:
 		if (rectangular || thickness == 1) {
 
@@ -190,7 +191,7 @@ html_redraw_border_plot(const int side,
 
 	case CSS_BORDER_STYLE_GROOVE:
 		light = 3 - light;
-		/* fall through */
+		fallthrough;
 	case CSS_BORDER_STYLE_RIDGE:
 		/* choose correct colours for each part of the border line */
 		if (light <= 1) {
@@ -300,7 +301,7 @@ html_redraw_border_plot(const int side,
 
 	case CSS_BORDER_STYLE_INSET:
 		light = (light + 2) % 4;
-		/* fall through */
+		fallthrough;
 	case CSS_BORDER_STYLE_OUTSET:
 		/* choose correct colours for each part of the border line */
 		switch (light) {
diff --git a/content/handlers/html/script.c b/content/handlers/html/script.c
index 962386d68..554fc4f70 100644
--- a/content/handlers/html/script.c
+++ b/content/handlers/html/script.c
@@ -495,6 +495,7 @@ exec_src_script(html_content *c,
 		switch (script_type) {
 		case HTML_SCRIPT_SYNC:
 			ret =  DOM_HUBBUB_HUBBUB_ERR | HUBBUB_PAUSED;
+			break;
 
 		case HTML_SCRIPT_ASYNC:
 			break;
diff --git a/content/handlers/html/table.c b/content/handlers/html/table.c
index 4ffcceab9..f8762e862 100644
--- a/content/handlers/html/table.c
+++ b/content/handlers/html/table.c
@@ -26,6 +26,7 @@
 #include <dom/dom.h>
 
 #include "utils/log.h"
+#include "utils/utils.h"
 #include "utils/talloc.h"
 #include "css/utils.h"
 
@@ -93,27 +94,27 @@ table_border_is_more_eyecatching(const css_unit_ctx *unit_len_ctx,
 
 	/* 3b -- sort by style */
 	switch (a->style) {
-	case CSS_BORDER_STYLE_DOUBLE: impact++; /* Fall through */
-	case CSS_BORDER_STYLE_SOLID:  impact++; /* Fall through */
-	case CSS_BORDER_STYLE_DASHED: impact++; /* Fall through */
-	case CSS_BORDER_STYLE_DOTTED: impact++; /* Fall through */
-	case CSS_BORDER_STYLE_RIDGE:  impact++; /* Fall through */
-	case CSS_BORDER_STYLE_OUTSET: impact++; /* Fall through */
-	case CSS_BORDER_STYLE_GROOVE: impact++; /* Fall through */
-	case CSS_BORDER_STYLE_INSET:  impact++; /* Fall through */
+	case CSS_BORDER_STYLE_DOUBLE: impact++; fallthrough;
+	case CSS_BORDER_STYLE_SOLID:  impact++; fallthrough;
+	case CSS_BORDER_STYLE_DASHED: impact++; fallthrough;
+	case CSS_BORDER_STYLE_DOTTED: impact++; fallthrough;
+	case CSS_BORDER_STYLE_RIDGE:  impact++; fallthrough;
+	case CSS_BORDER_STYLE_OUTSET: impact++; fallthrough;
+	case CSS_BORDER_STYLE_GROOVE: impact++; fallthrough;
+	case CSS_BORDER_STYLE_INSET:  impact++; fallthrough;
 	default:
 		break;
 	}
 
 	switch (b->style) {
-	case CSS_BORDER_STYLE_DOUBLE: impact--; /* Fall through */
-	case CSS_BORDER_STYLE_SOLID:  impact--; /* Fall through */
-	case CSS_BORDER_STYLE_DASHED: impact--; /* Fall through */
-	case CSS_BORDER_STYLE_DOTTED: impact--; /* Fall through */
-	case CSS_BORDER_STYLE_RIDGE:  impact--; /* Fall through */
-	case CSS_BORDER_STYLE_OUTSET: impact--; /* Fall through */
-	case CSS_BORDER_STYLE_GROOVE: impact--; /* Fall through */
-	case CSS_BORDER_STYLE_INSET:  impact--; /* Fall through */
+	case CSS_BORDER_STYLE_DOUBLE: impact--; fallthrough;
+	case CSS_BORDER_STYLE_SOLID:  impact--; fallthrough;
+	case CSS_BORDER_STYLE_DASHED: impact--; fallthrough;
+	case CSS_BORDER_STYLE_DOTTED: impact--; fallthrough;
+	case CSS_BORDER_STYLE_RIDGE:  impact--; fallthrough;
+	case CSS_BORDER_STYLE_OUTSET: impact--; fallthrough;
+	case CSS_BORDER_STYLE_GROOVE: impact--; fallthrough;
+	case CSS_BORDER_STYLE_INSET:  impact--; fallthrough;
 	default:
 		break;
 	}
@@ -128,20 +129,20 @@ table_border_is_more_eyecatching(const css_unit_ctx *unit_len_ctx,
 
 	/** \todo COL/COL_GROUP */
 	switch (a_src) {
-	case BOX_TABLE_CELL:       impact++; /* Fall through */
-	case BOX_TABLE_ROW:        impact++; /* Fall through */
-	case BOX_TABLE_ROW_GROUP:  impact++; /* Fall through */
-	case BOX_TABLE:            impact++; /* Fall through */
+	case BOX_TABLE_CELL:       impact++; fallthrough;
+	case BOX_TABLE_ROW:        impact++; fallthrough;
+	case BOX_TABLE_ROW_GROUP:  impact++; fallthrough;
+	case BOX_TABLE:            impact++; fallthrough;
 	default:
 		break;
 	}
 
 	/** \todo COL/COL_GROUP */
 	switch (b_src) {
-	case BOX_TABLE_CELL:       impact--; /* Fall through */
-	case BOX_TABLE_ROW:        impact--; /* Fall through */
-	case BOX_TABLE_ROW_GROUP:  impact--; /* Fall through */
-	case BOX_TABLE:            impact--; /* Fall through */
+	case BOX_TABLE_CELL:       impact--; fallthrough;
+	case BOX_TABLE_ROW:        impact--; fallthrough;
+	case BOX_TABLE_ROW_GROUP:  impact--; fallthrough;
+	case BOX_TABLE:            impact--; fallthrough;
 	default:
 		break;
 	}
diff --git a/content/handlers/image/webp.c b/content/handlers/image/webp.c
index da13316bc..c04c0efd2 100644
--- a/content/handlers/image/webp.c
+++ b/content/handlers/image/webp.c
@@ -142,7 +142,7 @@ webp_cache_convert(struct content *c)
 	default:
 		/* WebP has no ABGR function, fall back to default. */
 		webp_fmt.layout = BITMAP_LAYOUT_R8G8B8A8;
-		/* Fall through. */
+		fallthrough;
 	case BITMAP_LAYOUT_R8G8B8A8:
 		decoded = WebPDecodeRGBAInto(source_data, source_size, pixels,
 				rowstride * webpfeatures.height, rowstride);
diff --git a/content/handlers/javascript/duktape/dukky.c b/content/handlers/javascript/duktape/dukky.c
index c0a2749a9..a780b0067 100644
--- a/content/handlers/javascript/duktape/dukky.c
+++ b/content/handlers/javascript/duktape/dukky.c
@@ -385,7 +385,7 @@ static void dukky_html_element_class_from_tag_type(dom_html_element_type type,
 		break;
 	case DOM_HTML_ELEMENT_TYPE__COUNT:
 		assert(type != DOM_HTML_ELEMENT_TYPE__COUNT);
-		/* fallthrough */
+		fallthrough;
 	case DOM_HTML_ELEMENT_TYPE__UNKNOWN:
 		SET_HTML_CLASS(UNKNOWN)
 		break;
diff --git a/frontends/gtk/download.c b/frontends/gtk/download.c
index 63ca1c267..d1231634d 100644
--- a/frontends/gtk/download.c
+++ b/frontends/gtk/download.c
@@ -432,7 +432,7 @@ static gboolean nsgtk_download_update(gboolean force_update)
 		switch (dl->status) {
 		case NSGTK_DOWNLOAD_WORKING:
 			pulse_mode = TRUE;
-			/* Fall through */
+			fallthrough;
 
 		case NSGTK_DOWNLOAD_NONE:
 			dl->speed = dl->size_downloaded /
@@ -449,12 +449,13 @@ static gboolean nsgtk_download_update(gboolean force_update)
 
 			dl_ctx.num_active++;
 			update = TRUE;
-			/* Fall through */
+			fallthrough;
 
 		case NSGTK_DOWNLOAD_COMPLETE:
 			downloaded += dl->size_downloaded;
 			total += dl->size_total;
 			dls++;
+			fallthrough;
 
 		default:
 			;//Do nothing
diff --git a/frontends/gtk/search.c b/frontends/gtk/search.c
index 17447bbb7..f9a509f6e 100644
--- a/frontends/gtk/search.c
+++ b/frontends/gtk/search.c
@@ -270,6 +270,8 @@ nserror nsgtk_search_restyle(struct gtk_search *search)
 	case 4: /* Text icons only */
 		gtk_toolbar_set_style(GTK_TOOLBAR(search->bar),
 				      GTK_TOOLBAR_TEXT);
+		break;
+
 	default:
 		break;
 	}
diff --git a/frontends/windows/download.c b/frontends/windows/download.c
index 2b94e8363..cfd2bbbb7 100644
--- a/frontends/windows/download.c
+++ b/frontends/windows/download.c
@@ -169,7 +169,7 @@ nsws_download_event_callback(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
 		case IDOK:
 			if (download1->downloaded != download1->size)
 				return TRUE;
-			/* Fall through */
+			fallthrough;
 
 		case IDCANCEL:
 			nsws_download_clear_data(download1);
diff --git a/frontends/windows/window.c b/frontends/windows/window.c
index 10d16deaf..00e5a7e05 100644
--- a/frontends/windows/window.c
+++ b/frontends/windows/window.c
@@ -432,7 +432,7 @@ nsws_window_urlbar_callback(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
 			NSLOG(netsurf, INFO, "Destroyed font object");
 			DeleteObject(hFont);
 		}
-		/* Fall through */
+		fallthrough;
 
 	case WM_NCDESTROY:
 		/* remove properties if window is being destroyed */
diff --git a/utils/utils.h b/utils/utils.h
index 3995071cd..cb9e04b45 100644
--- a/utils/utils.h
+++ b/utils/utils.h
@@ -89,4 +89,31 @@
  */
 bool is_dir(const char *path);
 
+/**
+ * switch fall through
+ */
+#if defined __cplusplus && defined __has_cpp_attribute
+    #if __has_cpp_attribute(fallthrough) && __cplusplus >= __has_cpp_attribute(fallthrough)
+        #define fallthrough [[fallthrough]]
+    #elif __has_cpp_attribute(gnu::fallthrough) && __STDC_VERSION__ >= __has_cpp_attribute(gnu::fallthrough)
+        #define fallthrough [[gnu::fallthrough]]
+    #elif __has_cpp_attribute(clang::fallthrough) && __STDC_VERSION__ >= __has_cpp_attribute(clang::fallthrough)
+        #define fallthrough [[clang::fallthrough]]
+    #endif
+#elif defined __STDC_VERSION__ && defined __has_c_attribute
+    #if __has_c_attribute(fallthrough) && __STDC_VERSION__ >= __has_c_attribute(fallthrough)
+        #define fallthrough [[fallthrough]]
+    #endif
+#endif
+#if !defined fallthrough && defined __has_attribute
+    #if __has_attribute(__fallthrough__)
+        #define fallthrough __attribute__((__fallthrough__))
+    #endif
+#endif
+#if !defined fallthrough
+/*  early gcc and clang have no implicit fallthrough warning */
+    #define fallthrough do {} while(0)
+#endif
+
+
 #endif