refactor(diag): file-qualified diagnostic locations

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

1 files changed, 44 insertions, 0 deletions

diff --git a/include/cps/Diagnostics.h b/include/cps/Diagnostics.h
new file mode 100644
index 0000000..6f26292
--- /dev/null
+++ b/include/cps/Diagnostics.h
@@ -0,0 +1,44 @@
+#pragma once
+#include <cstdarg>
+#include <cstdio>
+#include <string>
+#include <vector>
+
+namespace cps {
+// Empty for single-source builds to preserve existing diagnostic text.
+inline std::string DiagnosticSource;
+inline std::string lineSuffix(int Line) {
+    return " at line " + std::to_string(Line) +
+           (DiagnosticSource.empty() ? "" : " in " + DiagnosticSource);
+}
+inline void sourceDiagnostic(int Line, const char *Format, ...) {
+    va_list Args, Copy;
+    va_start(Args, Format);
+    va_copy(Copy, Args);
+    int Size = std::vsnprintf(nullptr, 0, Format, Copy);
+    va_end(Copy);
+    if (Size < 0) { va_end(Args); return; }
+    std::vector<char> Buffer(Size + 1);
+    std::vsnprintf(Buffer.data(), Buffer.size(), Format, Args);
+    va_end(Args);
+    std::string Message(Buffer.data(), Size);
+    if (!DiagnosticSource.empty()) {
+        auto At = Message.find("at line ");
+        if (At != std::string::npos) {
+            auto End = Message.find_first_not_of("0123456789", At + 8);
+            Message.insert(End == std::string::npos ? Message.size() : End,
+                           " in " + DiagnosticSource);
+        } else {
+            auto Old = Message.find("(line ");
+            if (Old != std::string::npos) {
+                auto End = Message.find(')', Old);
+                Message.replace(Old, End - Old + 1, lineSuffix(Line).substr(1));
+            } else {
+                auto End = Message.find_last_not_of("\n");
+                Message.insert(End == std::string::npos ? 0 : End + 1, lineSuffix(Line));
+            }
+        }
+    }
+    std::fputs(Message.c_str(), stderr);
+}
+}