fixes #20107 (#20246) [backport]

1 files changed, 14 insertions, 0 deletions

diff --git a/compiler/ccgexprs.nim b/compiler/ccgexprs.nim
index 4c15101a9..1f16f458f 100644
--- a/compiler/ccgexprs.nim
+++ b/compiler/ccgexprs.nim
@@ -731,7 +731,21 @@ proc isCppRef(p: BProc; typ: PType): bool {.inline.} =
       skipTypes(typ, abstractInstOwned).kind in {tyVar} and
       tfVarIsPtr notin skipTypes(typ, abstractInstOwned).flags
 
+proc derefBlock(p: BProc, e: PNode, d: var TLoc) =
+  # We transform (block: x)[] to (block: x[])
+  let e0 = e[0]
+  var n = shallowCopy(e0)
+  for i in 0 ..< e0.len - 1:
+    n[i] = e0[i]
+  n[e0.len-1] = newTreeIT(nkHiddenDeref, e.info, e.typ, e0[e0.len-1])
+  expr p, n, d
+
 proc genDeref(p: BProc, e: PNode, d: var TLoc) =
+  if e.kind == nkHiddenDeref and e[0].kind in {nkBlockExpr, nkBlockStmt}:
+    # bug #20107. Watch out to not deref the pointer too late.
+    derefBlock(p, e, d)
+    return
+
   let mt = mapType(p.config, e[0].typ, mapTypeChooser(e[0]))
   if mt in {ctArray, ctPtrToArray} and lfEnforceDeref notin d.flags:
     # XXX the amount of hacks for C's arrays is incredible, maybe we should