[generator] Add netcoreapp3.1 support (#606)

The `netcoreapp3.1` target framework doesn't include `System.CodeDom`.
Remove use of CSharpCodeGenerator.

Author: jonpryor

src/Java.Interop.Tools.JavaCallableWrappers/Java.Interop.Tools.JavaCallableWrappers/IdentifierValidator.cs

@@ -41,6 +41,11 @@ public static string CreateValidIdentifier (string identifier, bool useEncodedRe
 returnvalidIdentifier.Replace(normalizedIdentifier,"_");
 }
 
+publicstaticboolIsValidIdentifier(stringidentifier)
+{
+return!validIdentifier.IsMatch(identifier);
+}
+
 // Makes uglier but unique identifiers by encoding each invalid character with its character value
 staticstringEncodeReplacement(Matchmatch)=>$"_x{(ushort)match.Value[0]}_";
 }

tools/generator/CodeGenerationOptions.cs

@@ -3,7 +3,9 @@
 usingSystem.Collections.Generic;
 usingSystem.IO;
 usingSystem.Linq;
-usingMicrosoft.CSharp;
+
+usingJava.Interop.Tools.JavaCallableWrappers;
+
 usingXamarin.Android.Binder;
 usingXamarin.AndroidTools.AnnotationSupport;
 
@@ -97,21 +99,29 @@ public string GetOutputName (string s)
 returnGetOutputName(s.Substring(0,idx))+'<'+String.Join(", ",typeParams.ToArray())+'>';
 }
 
-CSharpCodeProvidercode_provider=newCSharpCodeProvider();
-
 publicstringGetSafeIdentifier(stringname)
 {
+if(string.IsNullOrEmpty(name))
+returnname;
+
 // NOTE: "partial" differs in behavior on macOS vs. Windows, Windows reports "partial" as a valid identifier
 //	This check ensures the same output on both platforms
-if(name=="partial")
-returnname;
+switch(name){
+case"partial":returnname;
+// `this` isn't in TypeNameUtilities.reserved_keywords; special-case.
+case"this":return"this_";
+}
 
 // In the ideal world, it should not be applied twice.
 // Sadly that is not true in reality, so we need to exclude non-symbols
 // when replacing the argument name with a valid identifier.
 // (ReturnValue.ToNative() takes an argument which could be either an expression or mere symbol.)
-if(name.LastOrDefault()!=')'&&!name.Contains('.'))
-name=code_provider.IsValidIdentifier(name)?name:name+'_';
+if(name[name.Length-1]!=')'&&!name.Contains('.')&&!name.StartsWith("@")){
+if(!IdentifierValidator.IsValidIdentifier(name)||
+Array.BinarySearch(TypeNameUtilities.reserved_keywords,name)>=0){
+name=name+"_";
+}
+}
 returnname.Replace('$','_');
 }
 

tools/generator/Utilities/TypeNameUtilities.cs

@@ -11,7 +11,7 @@ public static class TypeNameUtilities
 {
 // These must be sorted for BinarySearch to work
 // Missing "this" because it's handled elsewhere as "this_"
-staticstring[]reserved_keywords=new[]{
+internalstaticstring[]reserved_keywords=new[]{
 "abstract","as","base","bool","break","byte","callback","case","catch","char","checked","class","const",
 "continue","decimal","default","delegate","do","double","else","enum","event","explicit","extern","false",
 "finally","fixed","float","for","foreach","goto","if","implicit","in","int","interface","internal",

tools/generator/generator.csproj

@@ -1,7 +1,7 @@
 <ProjectSdk="Microsoft.NET.Sdk">
 
  <PropertyGroup>
- <TargetFramework>net472</TargetFramework>
+ <TargetFrameworks>net472;netcoreapp3.1</TargetFrameworks>
  <OutputType>Exe</OutputType>
  <DefineConstants>$(DefineConstants);GENERATOR;HAVE_CECIL;JCW_ONLY_TYPE_NAMES</DefineConstants>
  <AppendTargetFrameworkToOutputPath>false</AppendTargetFrameworkToOutputPath>