Fix out of bounds in text extent computation (#77402)

Author: CyrusNajmabadi

src/EditorFeatures/CSharp/TextStructureNavigation/CSharpTextStructureNavigatorProvider.cs

@@ -97,7 +97,7 @@ protected override TextExtent GetExtentOfWordFromToken(ITextStructureNavigator n
                     contentStart++;
             }
 
-            var end = token.Span.End;
+            var end = Math.Max(contentStart, token.Span.End);
             var contentEnd = end;
 
             if (CharAt(contentEnd - 1) == '8')
@@ -115,6 +115,8 @@ protected override TextExtent GetExtentOfWordFromToken(ITextStructureNavigator n
                     contentEnd--;
             }
 
+            // Ensure that in error conditions like a naked `"` that we don't end up with invalid bounds.
+            contentEnd = Math.Max(contentStart, contentEnd);
             return (TextSpan.FromBounds(start, contentStart), TextSpan.FromBounds(contentStart, contentEnd), TextSpan.FromBounds(contentEnd, end));
         }
 

src/EditorFeatures/CSharpTest/TextStructureNavigation/TextStructureNavigatorTests.cs

@@ -561,4 +561,13 @@ public void TestClampStringLiteral(string content)
     {
         AssertExtent(content);
     }
+
+    [WpfTheory, WorkItem("https://github.com/dotnet/roslyn/issues/77401")]
+    [InlineData(@"{|Significant:""|}$$")]
+    [InlineData(@"{|Significant:""""""|}$$")]
+    [InlineData(@"""""""{|Significant:u8|}$$")]
+    public void TestClampStringLiteral_Invalid(string content)
+    {
+        AssertExtent(content);
+    }
 }