[Xamarin.Android.Build.Tasks] Add more warning codes

Context: #1560

* I investigated the code paths that led into the `LogWarning()` in
  `GenerateResourceDesigner.AddRename()`.  I could not find any way to
  hit that message with the current code.  Moreover, the only reports of
  the message I could find on the web were from capitalization
  mismatches, and those are now explicitly ignored by the use of the
  `StringComparison.OrdinalIgnoreCase` argument in the call to
  `string.Compare()`.  Since this message does not currently indicate an
  actionable problem, I changed it from a warning to a debug message.

* Neither of the warnings in
  `GetAdditionalResourcesFromAssemblies.AddAttributeValue()` is
  actionable for Xamarin.Android app developers.  The first warning can
  only arise if a new attribute name has been added to the `switch`
  statement in `DoExecute()`.  The second warning can only occur in a
  library that uses one of those attributes.  Since the attributes are
  not formally documented, they are currently only intended for use by
  the Xamarin team.  Since these warnings aren't aimed at end-users,
  they don't need to have their own codes.  So for now, I just updated
  the warnings to reuse the `errorCode`.

* The first warning in
  `GetAdditionalResourcesFromAssemblies.MakeSureLibraryIsInPlace()` is
  just an informational message.  The download step is *expected* to be
  skipped during design-time builds.  I changed the warning to a debug
  message accordingly.

* I changed the warning in `ReadAdditionalResourcesFromAssemblyCache` to
  a debug message because it is just informational.  For example, in the
  normal process of building application projects, the
  Xamarin.Android.Common.targets checks if `CacheFile` exists before it
  invokes the task, so an absent `CacheFile` is often normal.  In cases
  where the warning could be actionable for an end-user, the warning
  would indicate that something went wrong earlier when creating the
  `CacheFile` in `GetAdditionalResourcesFromAssemblies`, so even in that
  case this warning would not be needed because more actionable messages
  should come from the earlier task.  On top of that, this whole old
  mechanism of downloading external files is rarely used now that the
  large majority of the NuGet packages from the Xamarin team have been
  updated to use the newer Xamarin.Build.Download mechanism.

* I also changed the warnings in `ReadImportedLibrariesCache` and
 `ReadLibraryProjectImportsCache` to debug messages for similar reasons.
 A missing cache file in one of these tasks indicates that something
 went wrong during the corresponding earlier `GetImportedLibraries` or
 `ResolveLibraryProjectImports` task, so any actionable messages would
 need to get logged in the earlier task instead.

* The warnings in
  `ResolveAssemblies.ResolveRuntimeAssemblyForReferenceAssembly()`
  should not occur during normal use.  They both depend on *generated*
  content related to the NuGet target framework moniker.  Based on these
  considerations, I assigned just one shared warning code to both
  warnings for now.

Author: brendanzagaeski

Documentation/guides/messages/README.md

@@ -41,20 +41,24 @@
 + [XA0113](xa0113.md): Google Play requires that new applications must use a `$(TargetFrameworkVersion)` of v8.0 (API level 26) or above.
 + [XA0114](xa0114.md): Google Play requires that application updates must use a `$(TargetFrameworkVersion)` of v8.0 (API level 26) or above.
 + [XA0115](xa0115.md): Invalid value 'armeabi' in $(AndroidSupportedAbis). This ABI is no longer supported. Please update your project properties.
++ [XA0118](xa0118.md): Could not parse '{TargetMoniker}'
 
 ### XA1xxx Project Related
 
 + [XA1000](xa1000.md): There was an problem parsing {file}. This is likely due to incomplete or invalid xml.
 + [XA1001](xa1001.md): AndroidResgen: Warning while updating Resource XML '{filename}': {Message}
 + [XA1002](xa1002.md): We found a matching key '{Key}' for '{Item}'. But the casing was incorrect. Please correct the casing
 + [XA1003](xa1003.md): '{zip}' does not exist. Please rebuild the project.
++ [XA1004](xa1004.md): Attempting naive type name fixup for element with ID '{id}' and type '{managedType}'
 
 ### XA2xxx Linker
 
 ### XA3xxx AOT
 
 ### XA4xxx Code Generation
 
++ [XA4214](xa4214.md): Duplicate managed type found! Mappings between managed types and Java types must be unique. First Type: '{0}'; Second Type: '{1}'.
++ [XA4215](xa4215.md): Duplicate Java type found! Mappings between managed types and Java types must be unique. First Type: '{0}'; Second Type: '{1}'.
 + [XA4301](xa4301.md): : Apk already contains the item `xxx`.
 
 ### XA5xxx GCC and toolchain

Documentation/guides/messages/xa1004.md

@@ -0,0 +1,39 @@
+# Compiler Warning XA1004
+
+When [Layout Bindings and Code-Behind][code-behind] are enabled, this warning
+will be emitted for every layout element that has the `//*/@android:id`
+attribute set and uses a fully-qualified name for the element type.
+
+For example, the warning *will* be emitted for both of the following elements:
+
+```xml
+<android.widget.TextView
+    android:id="@+id/text1" />
+<Android.Widget.TextView
+    android:id="@+id/text2" />
+```
+
+But it will *not* be emitted for elements that use just an unqualified class
+name like:
+
+```xml
+<TextView
+    android:id="@+id/text1" />
+```
+
+The "naive type name fixup" tries to ensure that any fully-qualified type name
+is a C# name rather than a Java name. First it checks a short list of known
+mappings between Java namespaces and C# namespaces, such as the mapping of
+`android.view` to `Android.Views`. For any remaining namespaces, it splits the
+namespace on `.` and capitalizes each part.
+
+To resolve this warning, change each element to use its unqualified C# class
+name or add a [`xamarin:managedType`][code-behind-attributes] attribute to each
+element that specifies the fully qualified C# name.
+
+Example message:
+- `warning XA1004: Attempting naive type name fixup for element with ID '@+id/text1' and type 'android.widget.TextView'`  
+  `warning XA1004: If the above fixup fails, please add `xamarin:managedType` attribute to the element with fully qualified managed type name of the element.`
+
+[code-behind]: ../LayoutCodeBehind.md
+[code-behind-attributes]: ../LayoutCodeBehind.md#layouqt-xml-attributes

Documentation/guides/messages/xa4214.md

@@ -0,0 +1,9 @@
+# Compiler Warning XA4214
+
+If the same fully qualified C# type name exists in two or more assemblies and
+both C# types inherit from `Java.Lang.Object`, then the build process will only
+generate an Android Callable Wrapper for *one* of them.
+
+Example message:
+- `warning XA4214: Duplicate managed type found! Mappings between managed types and Java types must be unique. First Type: 'Library.Class1, Library1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'; Second Type: 'Library.Class1, Library2, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.`
+- `warning XA4214: References to the type 'Library.Class1' will refer to 'Library.Class1, Library1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.`

Documentation/guides/messages/xa4215.md

@@ -0,0 +1,8 @@
+# Compiler Error XA4215
+
+This error indicates that two or more C# types are emitting the same fully
+qualified Java type name. To resolve this error, change the `[Register]`
+attribute on one of the C# types to a different Java type name.
+
+Example message:
+- `error XA4215: Duplicate Java type found! Mappings between managed types and Java types must be unique. First Type: 'Library.Class1, Library1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'; Second Type: 'Library.Class2, Library1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'`

src/Xamarin.Android.Build.Tasks/Tasks/CalculateLayoutCodeBehind.cs

@@ -317,8 +317,8 @@ void CreateWidget (XPathNavigator current, string filePath, string androidNS, st
 					managedType = managedType.Substring (0, idx).Trim ();
 
 				if (mayNeedTypeFixup && (idx = managedType.LastIndexOf ('.')) >= 0) {
-					LogWarning ($"Attempting naive type name fixup for element with ID '{id}' and type '{managedType}'");
-					LogMessage ("If the above fixup fails, please add `tools:managedType` attribute to the element with fully qualified managed type name of the element");
+					LogCodedWarning ("XA1004", $"Attempting naive type name fixup for element with ID '{id}' and type '{managedType}'");
+					LogCodedWarning ("XA1004", "If the above fixup fails, please add `xamarin:managedType` attribute to the element with fully qualified managed type name of the element.");
 
 					oldType = managedType;
 					string ns = managedType.Substring (0, idx);

src/Xamarin.Android.Build.Tasks/Tasks/GenerateJavaStubs.cs

@@ -177,20 +177,23 @@ void Run (DirectoryAssemblyResolver res)
 
 				TypeDefinition conflict;
 				if (managed.TryGetValue (managedKey, out conflict)) {
-					Log.LogWarning (
+					Log.LogCodedWarning (
+							"XA4214",
 							"Duplicate managed type found! Mappings between managed types and Java types must be unique. " +
 							"First Type: '{0}'; Second Type: '{1}'.",
 							conflict.GetAssemblyQualifiedName (),
 							type.GetAssemblyQualifiedName ());
-					Log.LogWarning (
+					Log.LogCodedWarning (
+							"XA4214",
 							"References to the type '{0}' will refer to '{1}'.",
 							managedKey, conflict.GetAssemblyQualifiedName ());
 					continue;
 				}
 				if (java.TryGetValue (javaKey, out conflict)) {
-					Log.LogError (
+					Log.LogCodedError (
+							"XA4215",
 							"Duplicate Java type found! Mappings between managed types and Java types must be unique. " +
-							"First Type: '{0}'; Second Type: '{1}'",
+							"First Type: '{0}'; Second Type: '{1}'.",
 							conflict.GetAssemblyQualifiedName (),
 							type.GetAssemblyQualifiedName ());
 					keep_going = false;

src/Xamarin.Android.Build.Tasks/Tasks/GenerateResourceDesigner.cs

@@ -267,7 +267,7 @@ private void AddRename (string android, string user)
 					var ext = Path.GetExtension (android);
 					var dir = Path.GetDirectoryName (user);
 
-					Log.LogWarning ("Resource target names differ; got '{0}', expected '{1}'.",
+					Log.LogDebugMessage ("Resource target names differ; got '{0}', expected '{1}'.",
 						Path.Combine (dir, Path.GetFileName (to) + ext),
 						Path.Combine (dir, Path.GetFileName (curTo) + ext));
 				}

src/Xamarin.Android.Build.Tasks/Tasks/GetAdditionalResourcesFromAssemblies.cs

@@ -108,14 +108,14 @@ void AddAttributeValue (ICollection<string> items, CustomAttribute attr, string
 			bool isDirectory, string fullPath)
 		{
 			if (!attr.HasConstructorArguments || attr.ConstructorArguments.Count != 1) {
-				LogWarning ("Attribute {0} doesn't have expected one constructor agrument", attr.AttributeType.FullName);
+				LogCodedWarning (errorCode, "Attribute {0} doesn't have expected one constructor agrument", attr.AttributeType.FullName);
 				return;
 			}
 
 			CustomAttributeArgument arg = attr.ConstructorArguments.First ();
 			string path = arg.Value as string;
 			if (string.IsNullOrEmpty (path)) {
-				LogWarning ("Attribute {0} contructor argument is empty or not set to string", attr.AttributeType.FullName);
+				LogCodedWarning (errorCode, "Attribute {0} contructor argument is empty or not set to string", attr.AttributeType.FullName);
 				return;
 			}
 			path = SubstituteEnvVariables (path).TrimEnd (Path.DirectorySeparatorChar);
@@ -298,7 +298,7 @@ string MakeSureLibraryIsInPlace (string destinationBase, string url, string vers
 			string file = Path.Combine (zipDir, !uri.IsFile ? hash + ".zip" : Path.GetFileName (uri.AbsolutePath));
 			if (string.IsNullOrEmpty (extraPath) && (!File.Exists (file) || !IsValidDownload (file, sha1) || !MonoAndroidHelper.IsValidZip (file))) {
 				if (DesignTimeBuild) {
-					LogWarning ($"DesignTimeBuild={DesignTimeBuild}. Skipping download of {url}");
+					LogDebugMessage ($"DesignTimeBuild={DesignTimeBuild}. Skipping download of {url}");
 					return null;
 				}
 

src/Xamarin.Android.Build.Tasks/Tasks/ReadAdditionalResourcesFromAssemblyCache.cs

@@ -37,7 +37,7 @@ public override bool Execute ()
 			Log.LogDebugMessage ("Task ReadAdditionalResourcesFromAssemblyCache");
 			Log.LogDebugMessage ("  CacheFile: {0}", CacheFile);
 			if (!File.Exists (CacheFile)) {
-				Log.LogWarning ("{0} does not exist. No Additional Resources found", CacheFile);
+				Log.LogDebugMessage ("{0} does not exist. No Additional Resources found", CacheFile);
 				return !Log.HasLoggedErrors;
 			}
 			var doc = XDocument.Load (CacheFile);

src/Xamarin.Android.Build.Tasks/Tasks/ReadImportedLibrariesCache.cs

@@ -51,7 +51,7 @@ public override bool Execute ()
 			Log.LogDebugMessage ("Task ReadImportedLibrariesCache");
 			Log.LogDebugMessage ("  CacheFile: {0}", CacheFile);
 			if (!File.Exists (CacheFile)) {
-				Log.LogWarning ("{0} does not exist. No Imported Libraries found", CacheFile);
+				Log.LogDebugMessage ("{0} does not exist. No Imported Libraries found", CacheFile);
 				return !Log.HasLoggedErrors;
 			}
 			var doc = XDocument.Load (CacheFile);