GCC patch v2 description

gcc_component_ref_v2.patch

@@ -1,7 +1,49 @@
 From 0d2945f8e3c1b89b122fef0ded3973dfae2eb904 Mon Sep 17 00:00:00 2001
 From: York Jasper Niebuhr <yjnworkstation@gmail.com>
 Date: Thu, 30 Oct 2025 13:12:24 +0100
-Subject: [PATCH] c_parse_component_ref callback
+Subject: [PATCH] c, plugin: Add c_parse_component_ref callback
+
+This patch supersedes my earlier submission:
+https://gcc.gnu.org/pipermail/gcc-patches/2025-October/697934.html
+
+It adds the c_parse_component_ref callback that plugins can register
+using register_c_parse_component_ref_cb. The callback receives the
+parsed COMPONENT_REF tree and may replace it by returning a new tree.
+Replacements that are not type-compatible with the original are ignored.
+
+The callback allows plugins to observe or instrument struct member
+accesses that would otherwise be lost due to folding before the earliest
+possible plugin pass or hook. In particular, the fold_offsetof
+functionality removes all traces of type and member information in
+offsetof-like trees, leaving only an integer constant for plugins to
+inspect.
+
+A typical use case would be to replace a select set of COMPONENT_REF
+nodes with type-compatible expressions calling a placeholder function,
+e.g. __deferred_offsetof(type, member). These calls cannot be folded
+away and thus remain available for plugin analysis in later passes.
+Offsets not of interest can be left untouched, preserving their const
+qualification and use in static assertions.
+
+Allowing the callback to alter COMPONENT_REF nodes required minor
+adjustments to fold_offsetof, which assumes a specific input format.
+The parser paths that cannot guarantee that format after invoking the
+callback now use fold_offsetof_maybe(), which attempts to fold normally
+but, on failure, casts the unfolded expressions to the desired output
+type.
+
+If the callback is not used to alter COMPONENT_REF trees, there is **no
+change** in GCC’s behavior.
+
+Since this callback targets fairly niche use cases, I opted to not make
+it part of the public plugin API so there is no need for maintenance
+guarantees.
+
+**Changes since the first proposal:**
+  * Moved callback invocation to a higher level (the parser)
+  * The callback is no longer part of the public plugin API
+
+Signed-off-by: York Jasper Niebuhr <yjnworkstation@gmail.com>
 
 ---
  gcc/c-family/c-common.cc | 48 +++++++++++++++++++++------