fixes #25509; removes void fields from a named tuple type (#25515)

fixes #25509

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
(cherry picked from commit b51be75613)

compiler/semtypinst.nim

@@ -562,6 +562,26 @@ proc eraseVoidParams*(t: PType) =
       setLen t.n.sons, pos
       break
 
+proc eraseTupleVoidFields*(t: PType) =
+  ## Remove void fields from a named tuple type, compacting both `t.n`
+  ## (the field symbol nodes) and `t.sonsImpl` (the child types).
+  if t.n == nil: return  # anonymous tuple, nothing to compact
+  for i in 0..<t.kidsLen:
+    if t.n[i].kind == nkRecList or t[i].kind == tyVoid:
+      # found first void field, compact from here
+      var pos = i
+      for j in i+1..<t.kidsLen:
+        if t[j].kind != tyVoid and j < t.n.len and t.n[j].kind != nkRecList:
+          t.n[pos] = t.n[j]
+          t[pos] = t[j]
+          if t.n[pos].kind == nkSym:
+            t.n[pos].sym.position = pos
+          inc pos
+        # else: skip void entries
+      setLen t.n.sons, pos
+      t.setSonsLen pos
+      break
+
 proc skipIntLiteralParams*(t: PType; idgen: IdGenerator) =
   for i, p in t.ikids:
     if p == nil: continue
@@ -693,7 +713,7 @@ proc replaceTypeVarsTAux(cl: var TReplTypeVars, t: PType, isInstValue = false):
 
   of tyUserTypeClass:
     result = t
-  
+
   of tyStatic:
     if cl.c.matchedConcept != nil:
       # allow concepts to not instantiate statics for now
@@ -766,6 +786,8 @@ proc replaceTypeVarsTAux(cl: var TReplTypeVars, t: PType, isInstValue = false):
         propagateFieldFlags(result, result.n)
         if result.kind == tyObject and cl.c.computeRequiresInit(cl.c, result):
           result.flags.incl tfRequiresInit
+        if result.kind == tyTuple:
+          eraseTupleVoidFields(result)
 
       of tyProc:
         eraseVoidParams(result)

tests/tuples/ttuples_issues.nim

@@ -131,3 +131,47 @@ static:
 
 main()
 mainProc()
+
+
+block:
+  type
+    Tuple[N] = tuple
+      a: int
+      b: N
+
+    TupleVoid = Tuple[void]
+
+  var x: TupleVoid = (a: 1, )
+  doAssert x.a == 1
+
+block:
+  type W[N] = seq[tuple[b: N]]
+  var _: W[void]
+
+block:
+  type Tuple2[N] = tuple
+    a: int
+    b: N
+    c: int
+
+  var y: Tuple2[void] = (a: 10, c: 20)
+  doAssert y.a == 10
+  doAssert y.c == 20
+
+block:
+  type Outer[N] = tuple
+    inner: tuple[x: int, y: N]
+
+  var o: Outer[void] = (inner: (x: 3, ))
+  doAssert o.inner.x == 3
+
+block:
+  type Tup[T] = tuple
+    a: int
+    b: T
+
+  proc f[T](t: Tup[T]): int =
+    result = t.a
+
+  var z: Tup[void] = (a: 7, )
+  doAssert f(z) == 7