How it works...

Symbol analyzers register one or more symbol action callbacks to analyze symbol kinds of interest. Note that, unlike the default implementation that registered a delegate method named AnalyzeSymbol, we registered a lambda callback.

We specified interest in analyzing all the top-level symbol kinds that can have an enclosing type, namely types, methods, fields, properties, and events in the RegisterSymbolAction invocation:

context.RegisterSymbolAction(symbolContext =>
{
 ...
},
SymbolKind.NamedType,
SymbolKind.Method,
SymbolKind.Field,
SymbolKind.Event,
SymbolKind.Property);

The analyzer driver ensures that the registered lambda is invoked for all symbols of the registered interest kinds in the compilation.

Analysis skips the immediate enclosing type, as C# compiler already reports error CS0542, if a member has the same name as its enclosing type.

// Skip the immediate containing type, CS0542 already covers this case.
var outerType = symbolContext.Symbol.ContainingType?.ContainingType;

Core analysis works by looping over the outer types and comparing the name of the symbol in a symbol analysis context with the relevant outer types, until it finds a match, in which case, it reports a diagnostic; if the outer type has no containing type, it doesn t report a diagnostic.

while (outerType != null)
{
 // Check if the current outer type has the same name as the given member.
 if (symbolName.Equals(outerType.Name))
 {
  // For all such symbols, report a diagnostic.
  ...
 }

 outerType = outerType.ContainingType;
}