From 519e01e83bc8581639ed1d50b24a04683662e6c5 Mon Sep 17 00:00:00 2001
From: David Malcolm <dmalcolm@redhat.com>
Date: Thu, 23 Jan 2025 11:26:37 -0500
Subject: [PATCH 95/98] FIXME: add suggest_macro_expansion_problem

---
 gcc/c-family/known-headers.cc | 39 +++++++++++++++++++++++++++++++++--
 gcc/c-family/known-headers.h  |  2 +-
 libcpp/include/cpplib.h       |  2 +-
 3 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/gcc/c-family/known-headers.cc b/gcc/c-family/known-headers.cc
index 283edbbd8601..bac9bf2f84d1 100644
--- a/gcc/c-family/known-headers.cc
+++ b/gcc/c-family/known-headers.cc
@@ -298,11 +298,41 @@ get_cp_stdlib_header_for_string_macro_name (const char *name)
   return get_string_macro_hint (name, STDLIB_CPLUSPLUS);
 }
 
+/* Subclass of deferred_diagnostic for suggesting to the user
+   that something has gone wrong with expansion of a preprocessor macro.  */
+
+class suggest_macro_expansion_problem : public deferred_diagnostic
+{
+ public:
+  suggest_macro_expansion_problem (const cpp_hashnode *hashnode)
+  : deferred_diagnostic (cpp_macro_definition_location (hashnode)),
+    m_hashnode (hashnode)
+  {
+    gcc_assert (cpp_macro_p (hashnode));
+  }
+  ~suggest_macro_expansion_problem ()
+  {
+    if (is_suppressed_p ())
+      return;
+
+    location_t loc = get_location ();
+    if (loc <= BUILTINS_LOCATION)
+      return;
+
+    inform (loc,
+	    "%qs was defined as a preprocessor macro here",
+	    NODE_NAME (m_hashnode));
+  }
+
+ private:
+  const cpp_hashnode *m_hashnode;
+};
+
 /* Implementation of class suggest_missing_header.  */
 
 // FIXME
 
-std::unique_ptr<suggest_missing_header>
+std::unique_ptr<deferred_diagnostic>
 suggest_missing_header::maybe_make (location_t loc, const char *name,
 				    const char *header_hint)
 {
@@ -315,7 +345,12 @@ suggest_missing_header::maybe_make (location_t loc, const char *name,
 						 (const unsigned char *) (name),
 						 strlen (name)))
     if (cpp_macro_p (hashnode))
-      return nullptr; // TODO: or a different suggestion
+      {
+	if (cpp_user_macro_p (hashnode))
+	  return std::make_unique<suggest_macro_expansion_problem> (hashnode);
+	else
+	  return nullptr;
+      }
 
   // FIXME: use should_suggest_as_macro_p ?
 
diff --git a/gcc/c-family/known-headers.h b/gcc/c-family/known-headers.h
index fc78e2670553..8c595d1a01c6 100644
--- a/gcc/c-family/known-headers.h
+++ b/gcc/c-family/known-headers.h
@@ -32,7 +32,7 @@ extern const char *get_cp_stdlib_header_for_string_macro_name (const char *n);
 class suggest_missing_header : public deferred_diagnostic
 {
  public:
-  static std::unique_ptr<suggest_missing_header>
+  static std::unique_ptr<deferred_diagnostic>
   maybe_make (location_t loc, const char *name,
 	      const char *header_hint);
 
diff --git a/libcpp/include/cpplib.h b/libcpp/include/cpplib.h
index bc0d7714e96f..f0152ef0c2f4 100644
--- a/libcpp/include/cpplib.h
+++ b/libcpp/include/cpplib.h
@@ -1276,7 +1276,7 @@ inline bool cpp_keyword_p (cpp_hashnode *node)
 extern const unsigned char *cpp_macro_definition (cpp_reader *, cpp_hashnode *);
 extern const unsigned char *cpp_macro_definition (cpp_reader *, cpp_hashnode *,
 						  const cpp_macro *);
-inline location_t cpp_macro_definition_location (cpp_hashnode *node)
+inline location_t cpp_macro_definition_location (const cpp_hashnode *node)
 {
   const cpp_macro *macro = node->value.macro;
   return macro ? macro->line : 0;
-- 
2.49.0