Fix stack empty error for an embed outside an update block

src/SIL.Machine/Corpora/UpdateUsfmParserHandler.cs

@@ -413,10 +413,16 @@ protected override void EndNonVerseText(UsfmParserState state, ScriptureRef scri
 
         protected override void EndEmbedText(UsfmParserState state, ScriptureRef scriptureRef)
         {
+            // If this embed is outside an update block, create an update block just for this embed
+            bool embedOutsideOfBlock = _updateBlocks.Count == 0;
+            if (embedOutsideOfBlock)
+                StartUpdateBlock(new[] { scriptureRef });
             _updateBlocks
                 .Peek()
                 .AddEmbed(_embedTokens, markedForRemoval: _embedBehavior == UpdateUsfmMarkerBehavior.Strip);
             _embedTokens.Clear();
+            if (embedOutsideOfBlock)
+                EndUpdateBlock(state, new[] { scriptureRef });
         }
 
         public string GetUsfm(string stylesheetFileName = "usfm.sty")

tests/SIL.Machine.Tests/Corpora/UpdateUsfmParserHandlerTests.cs

@@ -1408,6 +1408,91 @@ public void GetUsfm_PreferExisting_AddRemark()
         AssertUsfmEquals(target, result);
     }
 
+    [Test]
+    public void UpdateBlock_FootnoteInPublishedChapterNumber()
+    {
+        List<UpdateUsfmRow> rows = [new UpdateUsfmRow(ScrRef("ESG 1:0/2:s"), "Update 1")];
+        string usfm =
+            @"\id ESG - Test
+\c 1
+\cp A \f + \fr A.1-3: \ft Some note.\f*
+\s Heading 1
+";
+        var usfmUpdateBlockHandler = new TestUsfmUpdateBlockHandler();
+        string target = UpdateUsfm(
+            rows,
+            usfm,
+            usfmUpdateBlockHandlers: [usfmUpdateBlockHandler],
+            textBehavior: UpdateUsfmTextBehavior.StripExisting,
+            paragraphBehavior: UpdateUsfmMarkerBehavior.Preserve,
+            embedBehavior: UpdateUsfmMarkerBehavior.Preserve,
+            styleBehavior: UpdateUsfmMarkerBehavior.Preserve
+        );
+
+        string result =
+            @"\id ESG
+\c 1
+\cp A \f + \fr A.1-3: \ft Some note.\f*
+\s Update 1
+";
+        AssertUsfmEquals(target, result);
+
+        Assert.That(usfmUpdateBlockHandler.Blocks.Count, Is.EqualTo(2));
+        AssertUpdateBlockEquals(
+            usfmUpdateBlockHandler.Blocks[0],
+            ["ESG 1:0/1:f"],
+            (UsfmUpdateBlockElementType.Embed, @"\f + \fr A.1-3: \ft Some note.\f*", false)
+        );
+        AssertUpdateBlockEquals(
+            usfmUpdateBlockHandler.Blocks[1],
+            ["ESG 1:0/2:s"],
+            (UsfmUpdateBlockElementType.Text, "Update 1 ", false),
+            (UsfmUpdateBlockElementType.Text, "Heading 1 ", true)
+        );
+    }
+
+    [Test]
+    public void UpdateBlock_FootnoteAtStartOfChapterWithPrecedingText()
+    {
+        List<UpdateUsfmRow> rows = [new UpdateUsfmRow(ScrRef("ESG 1:0/2:s"), "Update 1")];
+        string usfm =
+            @"\id ESG - Test
+\c 1
+Text 1\f + \fr A.1-3: \ft Some note.\f*
+\s Heading 1
+";
+        var usfmUpdateBlockHandler = new TestUsfmUpdateBlockHandler();
+        string target = UpdateUsfm(
+            rows,
+            usfm,
+            usfmUpdateBlockHandlers: [usfmUpdateBlockHandler],
+            textBehavior: UpdateUsfmTextBehavior.PreferNew,
+            paragraphBehavior: UpdateUsfmMarkerBehavior.Preserve,
+            embedBehavior: UpdateUsfmMarkerBehavior.Preserve,
+            styleBehavior: UpdateUsfmMarkerBehavior.Preserve
+        );
+
+        string result =
+            @"\id ESG - Test
+\c 1 Text 1\f + \fr A.1-3: \ft Some note.\f*
+\s Update 1
+";
+        AssertUsfmEquals(target, result);
+
+        Assert.That(usfmUpdateBlockHandler.Blocks.Count, Is.EqualTo(2));
+        AssertUpdateBlockEquals(
+            usfmUpdateBlockHandler.Blocks[0],
+            ["ESG 1:0/1:f"],
+            (UsfmUpdateBlockElementType.Embed, @"\f + \fr A.1-3: \ft Some note.\f*", false)
+        );
+        AssertUpdateBlockEquals(
+            usfmUpdateBlockHandler.Blocks[1],
+            ["ESG 1:0/2:s"],
+            (UsfmUpdateBlockElementType.Text, "Update 1 ", false),
+            (UsfmUpdateBlockElementType.Text, "Heading 1 ", true)
+        );
+    }
+
     private static ScriptureRef[] ScrRef(params string[] refs)
     {
         return refs.Select(r => ScriptureRef.Parse(r)).ToArray();