Fix implicit fallthroughs throughout Skia.

This CL is not fully comprehensive; for instance, it does not contain
fixes for backends that don't compile on Mac. But it does resolve the
vast majority of cases that trigger -Wimplicit-fallthrough.

A few minor bugs were found and fixed, but none that were likely to
affect normal operation.

Change-Id: I43487602b0d56200ce8b42702e04f66390d82f60
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/295916
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>

Author: johnstiles-google

dm/DMSrcSink.cpp

@@ -512,7 +512,7 @@ Result CodecSrc::draw(SkCanvas* canvas) const {
                             return Result::Skip(
                                 "Cannot decode frame %i to 565 (%s).", i, fPath.c_str());
                         }
-                        // Fall through.
+                        [[fallthrough]];
                     default:
                         return Result::Fatal(
                             "Couldn't getPixels for frame %i in %s.", i, fPath.c_str());

fuzz/FuzzMain.cpp

@@ -464,6 +464,7 @@ static void fuzz_img(sk_sp<SkData> bytes, uint8_t scale, uint8_t mode) {
                     SkDebugf("Incompatible colortype conversion\n");
                     // Crash to allow afl-fuzz to know this was a bug.
                     raise(SIGSEGV);
+                    break;
                 default:
                     SkDebugf("[terminated] Couldn't getPixels.\n");
                     return;
@@ -594,15 +595,15 @@ static void fuzz_img(sk_sp<SkData> bytes, uint8_t scale, uint8_t mode) {
                                 return;
                             }
                             // If the first subset succeeded, a later one should not fail.
-                            // fall through to failure
+                            [[fallthrough]];
                         case SkCodec::kUnimplemented:
                             if (0 == (x|y)) {
                                 // First subset is okay to return unimplemented.
                                 SkDebugf("[terminated] subset codec not supported\n");
                                 return;
                             }
                             // If the first subset succeeded, why would a later one fail?
-                            // fall through to failure
+                            [[fallthrough]];
                         default:
                             SkDebugf("[terminated] subset codec failed to decode (%d, %d, %d, %d) "
                                                   "with dimensions (%d x %d)\t error %d\n",

gm/dstreadshuffle.cpp

@@ -100,6 +100,7 @@ class DstReadShuffle : public GM {
                 SkFont      font(ToolUtils::create_portable_typeface(), 100);
                 font.setEmbolden(true);
                 canvas->drawString(text, 0.f, 100.f, font, *paint);
+                break;
             }
             default:
                 break;

gm/xfermodes.cpp

@@ -154,7 +154,7 @@ class XfermodesGM : public skiagm::GM {
                 canvas->saveLayer(&bounds, &p);
                 restoreNeeded = true;
                 p.setBlendMode(SkBlendMode::kSrcOver);
-                // Fall through.
+                [[fallthrough]];
             }
             case kQuarterClear_SrcType: {
                 SkScalar halfW = SkIntToScalar(W) / 2;
@@ -175,7 +175,7 @@ class XfermodesGM : public skiagm::GM {
                 SkScalar h = SkIntToScalar(H);
                 SkRect r = SkRect::MakeXYWH(x, y + h / 4, w, h * 23 / 60);
                 canvas->clipRect(r);
-                // Fall through.
+                [[fallthrough]];
             }
             case kRectangle_SrcType: {
                 SkScalar w = SkIntToScalar(W);
@@ -188,10 +188,10 @@ class XfermodesGM : public skiagm::GM {
             }
             case kSmallRectangleImageWithAlpha_SrcType:
                 m.postScale(SK_ScalarHalf, SK_ScalarHalf, x, y);
-                // Fall through.
+                [[fallthrough]];
             case kRectangleImageWithAlpha_SrcType:
                 p.setAlpha(0x88);
-                // Fall through.
+                [[fallthrough]];
             case kRectangleImage_SrcType: {
                 SkAutoCanvasRestore acr(canvas, true);
                 canvas->concat(m);

modules/skparagraph/src/ParagraphImpl.cpp

@@ -1055,8 +1055,12 @@ void ParagraphImpl::setState(InternalState state) {
             fBidiRegions.reset();
             fGraphemes16.reset();
             fCodepoints.reset();
+            [[fallthrough]];
+
         case kShaped:
             fClusters.reset();
+            [[fallthrough]];
+
         case kClusterized:
         case kMarked:
         case kLineBroken:
@@ -1065,12 +1069,15 @@ void ParagraphImpl::setState(InternalState state) {
             this->computeEmptyMetrics();
             this->resetShifts();
             fLines.reset();
+            [[fallthrough]];
+
         case kFormatted:
             fPicture = nullptr;
+            [[fallthrough]];
+
         case kDrawn:
+        default:
             break;
-    default:
-        break;
     }
 }
 

samplecode/SampleAAGeometry.cpp

@@ -278,6 +278,7 @@ static void set_path_verb(int index, SkPath::Verb v, SkPath* path, SkScalar w) {
                     switch (v) {
                         case SkPath::kConic_Verb:
                             weight = w;
+                            [[fallthrough]];
                         case SkPath::kQuad_Verb:
                             pts[2] = pts[1];
                             pts[1].fX = (pts[0].fX + pts[2].fX) / 2;
@@ -303,6 +304,7 @@ static void set_path_verb(int index, SkPath::Verb v, SkPath* path, SkScalar w) {
                             break;
                         case SkPath::kConic_Verb:
                             weight = w;
+                            [[fallthrough]];
                         case SkPath::kQuad_Verb:
                             break;
                         case SkPath::kCubic_Verb: {
@@ -325,6 +327,7 @@ static void set_path_verb(int index, SkPath::Verb v, SkPath* path, SkScalar w) {
                             break;
                         case SkPath::kConic_Verb:
                             weight = w;
+                            [[fallthrough]];
                         case SkPath::kQuad_Verb: {
                             SkDCubic dCubic;
                             dCubic.set(pts);

samplecode/SampleAnimatedImage.cpp

@@ -104,11 +104,10 @@ class SampleAnimatedImage : public Sample {
             switch (uni) {
                 case kPauseKey:
                     fRunning = !fRunning;
-                    if (fImage->isFinished()) {
-                        // fall through
-                    } else {
+                    if (!fImage->isFinished()) {
                         return true;
                     }
+                    [[fallthrough]];
                 case kResetKey:
                     fImage->reset();
                     fCurrentTime = fLastWallTime;

src/codec/SkBmpCodec.cpp

@@ -394,7 +394,7 @@ SkCodec::Result SkBmpCodec::ReadHeader(SkStream* stream, bool inIco,
                 inputFormat = kRLE_BmpInputFormat;
                 break;
             }
-            // Fall through
+            [[fallthrough]];
         case kPng_BmpCompressionMethod:
             // TODO: Decide if we intend to support this.
             //       It is unsupported in the previous version and

src/codec/SkPngCodec.cpp

@@ -1018,8 +1018,7 @@ SkCodec::Result SkPngCodec::initializeXforms(const SkImageInfo& dstInfo, const O
             if (this->getEncodedInfo().bitsPerComponent() != 16) {
                 break;
             }
-
-            // Fall through
+            [[fallthrough]];
         case SkEncodedInfo::kRGBA_Color:
         case SkEncodedInfo::kGray_Color:
             skipFormatConversion = this->colorXform();

src/codec/SkWebpCodec.cpp

@@ -143,7 +143,7 @@ std::unique_ptr<SkCodec> SkWebpCodec::MakeFromStream(std::unique_ptr<SkStream> s
             // sense to guess kBGRA which is likely closer to the final
             // output.  Otherwise, we might end up converting
             // BGRA->YUVA->BGRA.
-            // Fallthrough:
+            [[fallthrough]];
         case 2:
             // This is the lossless format (BGRA).
             if (hasAlpha) {