无法使用源生成器从系统库中访问属性参数

Question

我正试图使一个源生成器映射列从谷歌bigquery api客户端到类属性。我有麻烦从属性上的ColumnAttribute获得自定义列名。ConstructorArguments总是空的，columnAttribute.AttributeClass在这个样品中总是ErrorTypeSymbol。如果我尝试使用compilation.GetTypeByMetadataName("System.ComponentModel.DataAnnotations.Schema.ColumnAttribute")加载该类型，结果总是null。

using System.Collections.Immutable;
using System.Diagnostics;
using System.Text;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Text;
namespace BigQueryMapping;
[Generator]
public class BigQueryMapperGenerator : IIncrementalGenerator
{
public void Initialize(IncrementalGeneratorInitializationContext context)
{
// add marker attribute
context.RegisterPostInitializationOutput(ctx =>
ctx.AddSource("BigQueryMappedAttribute.g.cs", SourceText.From(Attribute, Encoding.UTF8)));
// add static interface
context.RegisterPostInitializationOutput(ctx =>
ctx.AddSource("BigQueryMappedInterface.g.cs", SourceText.From(Interface, Encoding.UTF8)));
// get classes
IncrementalValuesProvider<ClassDeclarationSyntax> classDeclarations = context.SyntaxProvider
.CreateSyntaxProvider(
predicate: static (s, _) => s is ClassDeclarationSyntax c && c.AttributeLists.Any(),
transform: static (ctx, _) => GetSemanticTargetForGeneration(ctx)
)
.Where(static m => m is not null)!;
IncrementalValueProvider<(Compilation Compilation, ImmutableArray<ClassDeclarationSyntax>Syntaxes)>
compilationAndClasses = context.CompilationProvider.Combine(classDeclarations.Collect());
context.RegisterSourceOutput(compilationAndClasses,
static (spc, source) => Execute(source.Compilation, source.Syntaxes, spc));
static ClassDeclarationSyntax? GetSemanticTargetForGeneration(GeneratorSyntaxContext context)
{
var classDeclarationSyntax = (ClassDeclarationSyntax)context.Node;
foreach (var attributeListSyntax in classDeclarationSyntax.AttributeLists)
{
foreach (var attributeSyntax in attributeListSyntax.Attributes)
{
var fullName = context.SemanticModel.GetTypeInfo(attributeSyntax).Type?.ToDisplayString();
if (fullName == "BigQueryMapping.BigQueryMappedAttribute")
return classDeclarationSyntax;
}
}
return null;
}
static void Execute(Compilation compilation, ImmutableArray<ClassDeclarationSyntax> classes,
SourceProductionContext context)
{
try
{
if (classes.IsDefaultOrEmpty)
return;
var distinctClasses = classes.Distinct();
var classesToGenerate = GetTypesToGenerate(compilation, distinctClasses, context.CancellationToken);
foreach (var classToGenerate in classesToGenerate)
{
var result = GeneratePartialClass(classToGenerate);
context.AddSource($"{classToGenerate.RowClass.Name}.g.cs", SourceText.From(result, Encoding.UTF8));
}
}
catch (Exception e)
{
var descriptor = new DiagnosticDescriptor(id: "BQD001",
title: "Error creating bigquery mapper",
messageFormat: "{0} {1}",
category: "BigQueryMapperGenerator",
DiagnosticSeverity.Error,
isEnabledByDefault: true);
context.ReportDiagnostic(Diagnostic.Create(descriptor, null, e.Message, e.StackTrace));
}
}
}
static IEnumerable<ClassToGenerate> GetTypesToGenerate(Compilation compilation,
IEnumerable<ClassDeclarationSyntax> classes,
CancellationToken ct)
{
var columnAttributeSymbol =
compilation.GetTypeByMetadataName("System.ComponentModel.DataAnnotations.Schema.ColumnAttribute");
foreach (var @class in classes)
{
Debug.WriteLine($"Checking class {@class}");
ct.ThrowIfCancellationRequested();
var semanticModel = compilation.GetSemanticModel(@class.SyntaxTree);
if (semanticModel.GetDeclaredSymbol(@class) is not INamedTypeSymbol classSymbol)
continue;
var info = new ClassToGenerate(classSymbol, new());
foreach (var member in classSymbol.GetMembers())
{
if (member is IPropertySymbol propertySymbol)
{
if (propertySymbol.DeclaredAccessibility == Accessibility.Public)
{
if (propertySymbol.SetMethod is not null)
{
var columnName = propertySymbol.Name;
var columnAttribute = propertySymbol.GetAttributes().FirstOrDefault(a =>
a.AttributeClass!.ToDisplayString() == "Column");
if (columnAttribute is not null)
{
if (!columnAttribute.ConstructorArguments.IsDefaultOrEmpty)
{
var nameArg = columnAttribute.ConstructorArguments.First();
if (nameArg.Value is string name)
{
columnName = name;
}
}
}
info.Properties.Add((columnName, propertySymbol));
}
}
}
}
yield return info;
}
}

static string GeneratePartialClass(ClassToGenerate c)
{
var sb = new StringBuilder();
sb.Append($@"// <auto-generated/>
namespace {c.RowClass.ContainingNamespace.ToDisplayString()}
{{
public partial class {c.RowClass.Name} : BigQueryMapping.IBigQueryGenerated<{c.RowClass.Name}>
{{
public static {c.RowClass.Name} FromBigQueryRow(Google.Cloud.BigQuery.V2.BigQueryRow row)
{{
return new {c.RowClass.Name}
{{");
foreach (var (columnName, property) in c.Properties)
{
// would like to check if key exists but don't see any sort of ContainsKey implemented on BigQueryRow
var tempName = $"___{property.Name}";
var basePropertyType = property.Type.WithNullableAnnotation(NullableAnnotation.None).ToDisplayString();
if (basePropertyType.EndsWith("?"))
{
basePropertyType = basePropertyType.Substring(default, basePropertyType.Length - 1);
}
sb.Append($@"
{property.Name} = row[""{columnName}""] is {basePropertyType} {tempName} ? {tempName} : default,");
}
sb.Append($@"
}};
}}
}}
}}");
return sb.ToString();
}
private record struct ClassToGenerate(INamedTypeSymbol RowClass,
List<(string ColumnName, IPropertySymbol Property)> Properties);
public const string Attribute = /* lang=csharp */ @"// <auto-generated/>
namespace BigQueryMapping {
[System.AttributeUsage(System.AttributeTargets.Class)]
public class BigQueryMappedAttribute : System.Attribute
{
}
}";
public const string Interface = /* lang=csharp */ @"// <auto-generated/>
namespace BigQueryMapping {
public interface IBigQueryGenerated<TRow> {
static TRow FromBigQueryRow(Google.Cloud.BigQuery.V2.BigQueryRow row) => throw new System.NotImplementedException();
}
}";
}

我已经尝试了System.ComponentModel.DataAnnotations.Schema.ColumnAttribute和通过context.RegisterPostInitializationOutput注入的自定义属性来获得类似的结果。我也试着重写这个使用ISourceGenerator而不是IIncrementalGenerator，并得到了相同的行为。我想知道我需要做什么才能让columnAttribute正确加载。

感谢您的帮助

Answer 1

很难通灵调试代码，但这确实跳出来了:

var columnAttribute = propertySymbol.GetAttributes().FirstOrDefault(a =>
a.AttributeClass!.ToDisplayString() == "Column");

我猜这里的类应该是完全限定名。前面已经获取了ColumnAttribute类型，所以更好的做法是将AttributeClass与该类型进行比较，而不是像这样进行字符串检查。

作为半相关的注释，如果您正在寻找带有特定属性注释的类型/成员，而不是自己做，我们有SyntaxValueProvider。ForAttributeWithMetadataName经过大量优化，以减少对Visual Studio的性能影响。它需要17.3或更高的版本，但只要你满意，它通常会帮助性能。