feat(preprocessor): add file-local conditional switches

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

1 files changed, 19 insertions, 0 deletions

diff --git a/include/cps/Preprocessor.h b/include/cps/Preprocessor.h
new file mode 100644
index 0000000..ebc2806
--- /dev/null
+++ b/include/cps/Preprocessor.h
@@ -0,0 +1,19 @@
+#pragma once
+#include <istream>
+#include <string>
+#include <vector>
+
+namespace cps {
+
+struct PreprocessedSource {
+    std::string Text;
+    // One entry per original source line, before processing that line's directive.
+    std::vector<bool> LibraryLines;
+    bool HadError = false;
+};
+
+// Switches and conditional nesting belong to this input only. Masked lines retain
+// their byte lengths and line endings so the lexer sees original source locations.
+PreprocessedSource preprocess(std::istream &Input);
+
+}