wcc: stamp fn-ptr-value call results from the callee fn-type

A call whose callee is a fn-VALUE (a fn-pointer struct field like w.emit(...),
or a local/param) had no free SK_FN entry, so exprtype's name lookup missed and
the N_CALL went nil-stamped (the fn-ptr-field class of the asserttyped gap
audit — 3 warns at smoke). When the name lookup misses, fall back to harec's
check_expr_call shape: read the result off the checked callee node's own type —
autodereference + dealias to the TY_FN, take its result (ref/harec/src/check.c
:1566-1581). Name lookup stays primary: a fn-NAME callee node carries its
return type, not its fn-type, so an N_TFN check first would mis-yield void for
a fn-returning-fn; only genuine fn-value callees reach the fallback.

Drives the 901 gap-corpus B count to 0 — with A/D already closed, only the
legitimate abort exemption (C) remains before the bail can arm. Byte-id holds
(cgen's fn-ptr detection is structural, independent of the stamp; the lib/io
return-forwarding site is cs==ww on both bootstrap combined.ww).

selfhost/cmd/w6c/main.combined.ww

@@ -12327,14 +12327,33 @@ fn exprtype(c: *checker, e: *node, hint: *node) *node = {
 				s = scopelookup(c.cur, nm);
 			};
 		};
-		if (s == nil) { return nil; };
+		if (s != nil) { if (s.skind == skind.SK_FN) { if (s.decl != nil) {
-		if (s.skind != skind.SK_FN) { return nil; };
-		if (s.decl == nil) { return nil; };
 			// fn-decl's lhs is the return-type AST node. Mirrors cstage
-		// cmd/wcc/check.c:984+ regular-CALL `n->type = build_fn_type(c,
+			// cmd/wcc/check.c:984+ regular-CALL `n->type =
-		// s->decl)->ret` shape.
+			// build_fn_type(c, s->decl)->ret` shape.
 			e.type_ = tinfofornode(c, s.decl.lhs): *void;
 			return s.decl.lhs;
+		}; }; };
+		// A callee that is a fn-VALUE — a fn-pointer struct field
+		// (`w.emit(...)`), local, or param — has no free SK_FN entry, so
+		// the name lookup above misses. Read the result off the checked
+		// callee node's own type instead: autodereference + dealias to
+		// the TY_FN, then take its result. Mirrors harec's check_expr_call
+		// `expr->result = type_dealias(check_autodereference(lvalue->
+		// result))->func.result` (ref/harec/src/check.c:1566-1581). The
+		// name path stays primary because a fn-NAME callee node in wwstage
+		// already carries its RETURN type (fn-decl.lhs), not its fn-type —
+		// so a `fn make() fn() void` callee would otherwise mis-yield void.
+		let ct: *node = resolvealias(c, unwrapbang(exprtype(c, callee, nil)));
+		for (ct != nil && ct.kind == nkind.N_TPTR) {
+			ct = resolvealias(c, unwrapbang(ct.lhs));
+		};
+		if (ct != nil) { if (ct.kind == nkind.N_TFN) {
+			let res: *node = ct.lhs;
+			e.type_ = tinfofornode(c, res): *void;
+			return res;
+		}; };
+		return nil;
 	};
 	if (k == nkind.N_DOT) {
 		// A.6.1.5a — fold cases only. Mirrors cstage cmd/wcc/check.c

selfhost/cmd/wcc/check.ww

@@ -2297,14 +2297,33 @@ fn exprtype(c: *checker, e: *node, hint: *node) *node = {
 				s = scopelookup(c.cur, nm);
 			};
 		};
-		if (s == nil) { return nil; };
+		if (s != nil) { if (s.skind == skind.SK_FN) { if (s.decl != nil) {
-		if (s.skind != skind.SK_FN) { return nil; };
-		if (s.decl == nil) { return nil; };
 			// fn-decl's lhs is the return-type AST node. Mirrors cstage
-		// cmd/wcc/check.c:984+ regular-CALL `n->type = build_fn_type(c,
+			// cmd/wcc/check.c:984+ regular-CALL `n->type =
-		// s->decl)->ret` shape.
+			// build_fn_type(c, s->decl)->ret` shape.
 			e.type_ = tinfofornode(c, s.decl.lhs): *void;
 			return s.decl.lhs;
+		}; }; };
+		// A callee that is a fn-VALUE — a fn-pointer struct field
+		// (`w.emit(...)`), local, or param — has no free SK_FN entry, so
+		// the name lookup above misses. Read the result off the checked
+		// callee node's own type instead: autodereference + dealias to
+		// the TY_FN, then take its result. Mirrors harec's check_expr_call
+		// `expr->result = type_dealias(check_autodereference(lvalue->
+		// result))->func.result` (ref/harec/src/check.c:1566-1581). The
+		// name path stays primary because a fn-NAME callee node in wwstage
+		// already carries its RETURN type (fn-decl.lhs), not its fn-type —
+		// so a `fn make() fn() void` callee would otherwise mis-yield void.
+		let ct: *node = resolvealias(c, unwrapbang(exprtype(c, callee, nil)));
+		for (ct != nil && ct.kind == nkind.N_TPTR) {
+			ct = resolvealias(c, unwrapbang(ct.lhs));
+		};
+		if (ct != nil) { if (ct.kind == nkind.N_TFN) {
+			let res: *node = ct.lhs;
+			e.type_ = tinfofornode(c, res): *void;
+			return res;
+		}; };
+		return nil;
 	};
 	if (k == nkind.N_DOT) {
 		// A.6.1.5a — fold cases only. Mirrors cstage cmd/wcc/check.c

selfhost/cmd/wwdump/main.combined.ww

@@ -12327,14 +12327,33 @@ fn exprtype(c: *checker, e: *node, hint: *node) *node = {
 				s = scopelookup(c.cur, nm);
 			};
 		};
-		if (s == nil) { return nil; };
+		if (s != nil) { if (s.skind == skind.SK_FN) { if (s.decl != nil) {
-		if (s.skind != skind.SK_FN) { return nil; };
-		if (s.decl == nil) { return nil; };
 			// fn-decl's lhs is the return-type AST node. Mirrors cstage
-		// cmd/wcc/check.c:984+ regular-CALL `n->type = build_fn_type(c,
+			// cmd/wcc/check.c:984+ regular-CALL `n->type =
-		// s->decl)->ret` shape.
+			// build_fn_type(c, s->decl)->ret` shape.
 			e.type_ = tinfofornode(c, s.decl.lhs): *void;
 			return s.decl.lhs;
+		}; }; };
+		// A callee that is a fn-VALUE — a fn-pointer struct field
+		// (`w.emit(...)`), local, or param — has no free SK_FN entry, so
+		// the name lookup above misses. Read the result off the checked
+		// callee node's own type instead: autodereference + dealias to
+		// the TY_FN, then take its result. Mirrors harec's check_expr_call
+		// `expr->result = type_dealias(check_autodereference(lvalue->
+		// result))->func.result` (ref/harec/src/check.c:1566-1581). The
+		// name path stays primary because a fn-NAME callee node in wwstage
+		// already carries its RETURN type (fn-decl.lhs), not its fn-type —
+		// so a `fn make() fn() void` callee would otherwise mis-yield void.
+		let ct: *node = resolvealias(c, unwrapbang(exprtype(c, callee, nil)));
+		for (ct != nil && ct.kind == nkind.N_TPTR) {
+			ct = resolvealias(c, unwrapbang(ct.lhs));
+		};
+		if (ct != nil) { if (ct.kind == nkind.N_TFN) {
+			let res: *node = ct.lhs;
+			e.type_ = tinfofornode(c, res): *void;
+			return res;
+		}; };
+		return nil;
 	};
 	if (k == nkind.N_DOT) {
 		// A.6.1.5a — fold cases only. Mirrors cstage cmd/wcc/check.c

test/wcc/901_asserttyped_gap.c

@@ -21,7 +21,7 @@
  *
  * Gap classes (counts verified empirically at this revision):
  *   A  module-qual N_DOT call result   checked_test   0  (closed)
- *   B  fn-ptr struct-field call         smoke          3
+ *   B  fn-ptr struct-field call         smoke          0  (closed)
  *   C  abort intrinsic callee           utf8           8
  *   D  module-leaf == type/fn name      fnmatch        0  (closed)
  *   D  module-leaf == type/fn name      random         0  (closed)
@@ -109,7 +109,7 @@ main(void)
 		{ "lib/math/checked/checked_test.combined.ww",
 		  "A module-qual N_DOT call result", 0 },
 		{ "selfhost/test/smoke.combined.ww",
-		  "B fn-ptr struct-field call", 3 },
+		  "B fn-ptr struct-field call", 0 },
 		{ "lib/encoding/utf8/utf8.combined.ww",
 		  "C abort intrinsic callee", 8 },
 		{ "lib/fnmatch/fnmatchtest.combined.ww",
@@ -151,6 +151,6 @@ main(void)
 		return 1;
 	}
 	printf("asserttyped_gap: ww-stage checker warn set matches manifest "
-	    "on %d gap-corpus fixtures (B+C pinned, A+D closed)\n", n);
+	    "on %d gap-corpus fixtures (C pinned, A+B+D closed)\n", n);
 	return 0;
 }