Fix for doc generation failing on repeated compilations (microsoft#242)

Author: codingupastorm

src/QsCompiler/DocumentationParser/DocNamespace.cs

@@ -220,14 +220,21 @@ string GetItemUid(YamlNode item)
                 }
             }
 
-            // Now add our new items
+            // Now add our new items, overwriting if they already exist
             foreach (var item in items)
             {
                 var typeKey = ToSequenceKey(item.ItemType);
                 SortedDictionary<string, YamlNode> typeList;
                 if (itemTypeNodes.TryGetValue(typeKey, out typeList))
                 {
-                    typeList.Add(item.Uid, item.ToNamespaceItem());
+                    if (typeList.ContainsKey(item.Uid))
+                    {
+                        // TODO: Emit a warning log / diagnostic. What is the accepted way to do that here?
+                        // $"Documentation for {item.Uid} already exists in this folder and will be overwritten.
+                        // It's recommended to compile docs to a new folder to avoid deleted files lingering."
+                    }
+
+                    typeList[item.Uid] = item.ToNamespaceItem();
                 }
             }
 

src/QsCompiler/Tests.Compiler/CommandLineTests.fs

@@ -180,6 +180,13 @@ let ``generate docs`` () =
     Assert.True (existsAndNotEmpty nsDoc)
     Assert.True (existsAndNotEmpty opDoc)
 
+    // Verify that we can compile repeatedly without errors despite docs already existing.
+    let result2 = Program.Main args
+    Assert.Equal(ReturnCode.SUCCESS, result2) 
+    Assert.True (existsAndNotEmpty toc)
+    Assert.True (existsAndNotEmpty nsDoc)
+    Assert.True (existsAndNotEmpty opDoc)
+
 
 [<Fact>]
 let ``find path relative`` () =