don't crash an app if we got empty run during text shaping (#821)

* don't crash an app if we got empty run during text shaping

* on windows and linux it may produce some glyph

skiko/src/commonMain/cpp/common/include/TextLineRunHandler.hh

@@ -56,6 +56,7 @@ public:
 
     void commitRunBuffer(const RunInfo& info) override {
         TextLine::Run& run = fLine->fRuns.back();
+        if (0 < info.glyphCount) {
             int32_t glyph = 0;
             int32_t graphemesInGlyph = 1;
             SkScalar glyphLeft = run.fPos[glyph].fX;
@@ -84,6 +85,7 @@ public:
                     glyphLeft = glyphRight;
                 }
             }
+        }
         fPosition += info.fAdvance.fX;
     }
 

skiko/src/commonMain/kotlin/org/jetbrains/skia/shaper/Shaper.kt

@@ -195,8 +195,7 @@ class Shaper internal constructor(ptr: NativePointer) : Managed(ptr, _FinalizerH
             Stats.onNativeCall()
             ManagedString(text).use { managedString ->
                 interopScope {
-                    TextLine(
-                        _nShapeLine(
+                    val linePtr = _nShapeLine(
                         _ptr,
                         managedString._ptr,
                         getPtr(font),
@@ -204,7 +203,8 @@ class Shaper internal constructor(ptr: NativePointer) : Managed(ptr, _FinalizerH
                         optsFeatures = arrayOfFontFeaturesToInterop(opts.features),
                         optsBooleanProps = opts._booleanPropsToInt()
                     )
-                    )
+                    require(linePtr != NullPointer) { "Shape line: $text returned nullptr" }
+                    TextLine(linePtr)
                 }
 
             }

skiko/src/commonTest/kotlin/org/jetbrains/skia/TextLineTest.kt

 package org.jetbrains.skiko
 
-import org.jetbrains.skia.Font
-import org.jetbrains.skia.ManagedString
-import org.jetbrains.skia.TextLine
-import org.jetbrains.skia.Typeface
+import org.jetbrains.skia.*
 import org.jetbrains.skia.impl.use
+import org.jetbrains.skia.shaper.ShapingOptions
 import kotlin.test.Test
 import kotlin.test.assertContentEquals
 import kotlin.test.assertEquals
@@ -227,4 +225,11 @@ class TextLineTest {
         assertCloseEnough(expected = 48.0f, actual = textLine.getCoordAtOffset(2), epsilon = eps)
         assertCloseEnough(expected = 69.0f, actual = textLine.getCoordAtOffset(3), epsilon = eps)
     }
+
+    @Test
+    fun dontCrashOnStringsWithoutGlyphs() = runTest {
+        val failedOn = "\uFE0F" // Variation Selector-16
+        val textLine = TextLine.make(failedOn, jbMono36(), ShapingOptions.DEFAULT)
+        assertCloseEnough(expected = 0f, actual = textLine.width)
+    }
 }