feat(classes): warn when method declarations shadow fields

Retain parameter source lines for warnings and preserve field access
prefix validation when distinguishing fields from methods.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

4 files changed, 18 insertions, 1 deletions

diff --git a/lib/CodeGen/ConstantGen.cc b/lib/CodeGen/ConstantGen.cc
index 12bf4b1..58913e4 100644
--- a/lib/CodeGen/ConstantGen.cc
+++ b/lib/CodeGen/ConstantGen.cc
@@ -1,4 +1,5 @@
 #include "cps/CodeGen.h"
+#include <cstdio>
 
 using namespace llvm;
 using namespace cps;
@@ -15,6 +16,16 @@ void CodeGen::emitScopedBlock(const std::vector<std::unique_ptr<StmtAST>> &Body)
     ConstantScopes.pop_back();
 }
 
+void CodeGen::warnMemberShadow(const std::string &Name, int Line) const {
+    if (CurrentClass.empty()) return;
+    const TypeInfo *Class = resolveType(CurrentClass);
+    const RecordPayload *Record = Class ? Class->asRecord() : nullptr;
+    if (Record && Record->findField(Name)) {
+        fprintf(stderr, "warning: Declaration of %s shadows a field of class %s at line %d\n",
+                Name.c_str(), CurrentClass.c_str(), Line);
+    }
+}
+
 bool CodeGen::prepareSymbolDeclaration(const std::string &Name, bool IsConstant) {
     if (!CurrentClass.empty() && sameIdentifier(Name, "this")) {
         reportError("Cannot redeclare this inside a method");
@@ -31,6 +42,7 @@ bool CodeGen::prepareSymbolDeclaration(const std::string &Name, bool IsConstant)
     } else if (IsConstant) {
         Scope.Saved.emplace(Name, std::nullopt);
     }
+    warnMemberShadow(Name, DiagnosticLine);
     return true;
 }
 
diff --git a/lib/CodeGen/StatementGen.cc b/lib/CodeGen/StatementGen.cc
index c55aebe..2443877 100644
--- a/lib/CodeGen/StatementGen.cc
+++ b/lib/CodeGen/StatementGen.cc
@@ -23,6 +23,8 @@ void CodeGen::emitStmt(StmtAST *Stmt) {
 
     if (auto *FuncDef = dynamic_cast<FunctionDefAST*>(Stmt)) {
         SaveAndRestore<std::string> ClassContext(CurrentClass, FuncDef->getProto()->getOwnerClass());
+        for (const auto &Param : FuncDef->getProto()->getParams())
+            warnMemberShadow(Param.Name, Param.Line ? Param.Line : DiagnosticLine);
         BasicBlock *SavedBlock = Builder->GetInsertBlock();
         // Function bodies get a fresh array scope (metadata SSA values belong
         // to the emitting function), mirroring FunctionGen's Symbols handling.
diff --git a/lib/Parser/ParserFunction.cc b/lib/Parser/ParserFunction.cc
index 1aef756..ad187c8 100644
--- a/lib/Parser/ParserFunction.cc
+++ b/lib/Parser/ParserFunction.cc
@@ -51,6 +51,7 @@ std::optional<std::vector<ParamDecl>> Parser::ParsePrototypeArgs(bool AllowByRef
             return std::nullopt;
         }
         ParamDecl P;
+        P.Line = Lex.getLine();
         P.Name = Lex.IdentifierStr;
         P.Mode = Current;
         getNextToken();
diff --git a/lib/Parser/ParserType.cc b/lib/Parser/ParserType.cc
index 0d664d0..dab71a1 100644
--- a/lib/Parser/ParserType.cc
+++ b/lib/Parser/ParserType.cc
@@ -124,7 +124,9 @@ std::optional<std::vector<RecordFieldDecl>> Parser::ParseRecordBody(
         if (AtField()) {
             // Class fields default to public, like record fields.
             bool IsPublic = CurTok != tok_private;
-            if (IsClass && (CurTok == tok_public || CurTok == tok_private)) getNextToken();
+            if (IsClass && (CurTok == tok_public || CurTok == tok_private) &&
+                (Lex.peekToken() == tok_function || Lex.peekToken() == tok_procedure))
+                getNextToken();
             if (IsClass && (CurTok == tok_function || CurTok == tok_procedure)) {
                 auto Method = CurTok == tok_function ? ParseFunction(Name, IsPublic)
                                                     : ParseProcedure(Name, IsPublic);