refactor(codegen): share file keyword filename operand emission

EOF, OPENFILE, READFILE and CLOSEFILE each rejected a whole-array filename
and then emitted it as a C string. Route them through a private
emitFileNameOperand helper; diagnostics are unchanged. WRITEFILE keeps its
own combined check.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

3 files changed, 15 insertions, 20 deletions

diff --git a/include/cps/CodeGen.h b/include/cps/CodeGen.h
index 73068bf..2d77284 100644
--- a/include/cps/CodeGen.h
+++ b/include/cps/CodeGen.h
@@ -128,6 +128,7 @@ class CodeGen {
     llvm::Value *emitStringFromCString(llvm::Value *Text);
     llvm::Value *emitStringCString(llvm::Value *Value);
     llvm::Value *emitCStringExpr(ExprAST *Expr);
+    llvm::Value *emitFileNameOperand(ExprAST *E, const char *Keyword);
     bool containsString(const TypeInfo *Type) const;
     std::unique_ptr<TypeSystem> Types;
 
diff --git a/lib/CodeGen/ExpressionGen.cc b/lib/CodeGen/ExpressionGen.cc
index 3377a39..ece055a 100644
--- a/lib/CodeGen/ExpressionGen.cc
+++ b/lib/CodeGen/ExpressionGen.cc
@@ -225,11 +225,7 @@ Value *CodeGen::emitCall(const std::string &Callee,
         return Memory->emitRelease(Address, Line);
     }
     if (Name == "EOF") {
-        if (isWholeArrayVar(ArgExprs[0].get())) {
-            reportError("Cannot use a whole array as the EOF filename");
-            return nullptr;
-        }
-        Value *FileName = emitCStringExpr(ArgExprs[0].get());
+        Value *FileName = emitFileNameOperand(ArgExprs[0].get(), "EOF");
         if (!FileName) return nullptr;
         return Files->emitEof(FileName, Line);
     }
diff --git a/lib/CodeGen/StatementGen.cc b/lib/CodeGen/StatementGen.cc
index 40fe394..f4cd661 100644
--- a/lib/CodeGen/StatementGen.cc
+++ b/lib/CodeGen/StatementGen.cc
@@ -239,11 +239,7 @@ void CodeGen::emitStmtImpl(StmtAST *Stmt) {
     }
 
     if (auto *Open = dynamic_cast<OpenFileStmtAST*>(Stmt)) {
-        if (isWholeArrayVar(Open->getFileName())) {
-            reportError("Cannot use a whole array as the OPENFILE filename");
-            return;
-        }
-        Value *Name = emitCStringExpr(Open->getFileName());
+        Value *Name = emitFileNameOperand(Open->getFileName(), "OPENFILE");
         if (!Name) return;
         Files->emitOpen(Name, Open->getMode(), Open->getLine());
         return;
@@ -265,11 +261,7 @@ void CodeGen::emitStmtImpl(StmtAST *Stmt) {
                         Read->getVarName().c_str(), Info->TypeName.c_str());
             return;
         }
-        if (isWholeArrayVar(Read->getFileName())) {
-            reportError("Cannot use a whole array as the READFILE filename");
-            return;
-        }
-        Value *Name = emitCStringExpr(Read->getFileName());
+        Value *Name = emitFileNameOperand(Read->getFileName(), "READFILE");
         if (!Name) return;
         Value *LineStr = Files->emitRead(Name, Read->getLine());
         if (!LineStr) return;
@@ -302,11 +294,7 @@ void CodeGen::emitStmtImpl(StmtAST *Stmt) {
     }
 
     if (auto *Close = dynamic_cast<CloseFileStmtAST*>(Stmt)) {
-        if (isWholeArrayVar(Close->getFileName())) {
-            reportError("Cannot use a whole array as the CLOSEFILE filename");
-            return;
-        }
-        Value *Name = emitCStringExpr(Close->getFileName());
+        Value *Name = emitFileNameOperand(Close->getFileName(), "CLOSEFILE");
         if (!Name) return;
         Files->emitClose(Name, Close->getLine());
         return;
@@ -346,3 +334,13 @@ void CodeGen::emitStmtImpl(StmtAST *Stmt) {
         return;
     }
 }
+
+// File keywords take their filename as a STRING-valued expression; a whole
+// array is rejected before evaluation.
+Value *CodeGen::emitFileNameOperand(ExprAST *E, const char *Keyword) {
+    if (isWholeArrayVar(E)) {
+        reportError("Cannot use a whole array as the %s filename", Keyword);
+        return nullptr;
+    }
+    return emitCStringExpr(E);
+}