Rollup merge of #136107 - dingxiangfei2009:coerce-pointee-wellformed, r=compiler-errors

Introduce CoercePointeeWellformed for coherence checks at typeck stage

Fix #135206

This is the first PR to introduce the "wellformedness" check for `derive(CoercePointee)`.

This patch introduces a new error code to cover all the prerequisites of the said macro. The checks that is enforced with this patch is whether the data is indeed `struct` and whether the layout is set to `repr(transparent)`.

A following series of patch will arrive later to address the following concern.
1. #135217 so that we would only admit one single coercion on one type parameter, and leave the rest for future consideration in tandem of development of other coercion rules.
1. Enforcement of data field requirements.

**An open question** is whether there is a good schema to encode the `#[pointee]` as well, so that we could also check if the `#[pointee]` type parameter is indeed `?Sized`.

``@rustbot`` label F-derive_coerce_pointee

compiler/rustc_expand/src/build.rs

@@ -1,7 +1,8 @@
 use rustc_ast::ptr::P;
 use rustc_ast::util::literal;
 use rustc_ast::{
-    self as ast, AttrVec, BlockCheckMode, Expr, LocalKind, MatchKind, PatKind, UnOp, attr, token,
+    self as ast, AnonConst, AttrVec, BlockCheckMode, Expr, LocalKind, MatchKind, PatKind, UnOp,
+    attr, token,
 };
 use rustc_span::source_map::Spanned;
 use rustc_span::{DUMMY_SP, Ident, Span, Symbol, kw, sym};
@@ -138,6 +139,42 @@ impl<'a> ExtCtxt<'a> {
         }
     }
 
+    pub fn lifetime_param(
+        &self,
+        span: Span,
+        ident: Ident,
+        bounds: ast::GenericBounds,
+    ) -> ast::GenericParam {
+        ast::GenericParam {
+            id: ast::DUMMY_NODE_ID,
+            ident: ident.with_span_pos(span),
+            attrs: AttrVec::new(),
+            bounds,
+            is_placeholder: false,
+            kind: ast::GenericParamKind::Lifetime,
+            colon_span: None,
+        }
+    }
+
+    pub fn const_param(
+        &self,
+        span: Span,
+        ident: Ident,
+        bounds: ast::GenericBounds,
+        ty: P<ast::Ty>,
+        default: Option<AnonConst>,
+    ) -> ast::GenericParam {
+        ast::GenericParam {
+            id: ast::DUMMY_NODE_ID,
+            ident: ident.with_span_pos(span),
+            attrs: AttrVec::new(),
+            bounds,
+            is_placeholder: false,
+            kind: ast::GenericParamKind::Const { ty, kw_span: DUMMY_SP, default },
+            colon_span: None,
+        }
+    }
+
     pub fn trait_ref(&self, path: ast::Path) -> ast::TraitRef {
         ast::TraitRef { path, ref_id: ast::DUMMY_NODE_ID }
     }