From c0922ce1fed670f99cdffa79526ee2e4507b4a84 Mon Sep 17 00:00:00 2001
From: metagn <metagngn@gmail.com>
Date: Tue, 25 Nov 2025 20:46:30 +0300
Subject: [PATCH 1/3] consider generic param type as typedesc in tuple type
 expressions

fixes #25312
---
 compiler/semexprs.nim                   |  4 ++--
 tests/tuples/tgenericparamtypetuple.nim | 25 +++++++++++++++++++++++++
 2 files changed, 27 insertions(+), 2 deletions(-)
 create mode 100644 tests/tuples/tgenericparamtypetuple.nim

diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index 31b3770459d71..b74d1adc66efc 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -3064,10 +3064,10 @@ proc semTupleConstr(c: PContext, n: PNode, flags: TExprFlags; expectedType: PTyp
   var isTupleType: bool = false
   if tupexp.len > 0: # don't interpret () as type
     internalAssert c.config, tupexp.kind == nkTupleConstr
-    isTupleType = tupexp[0].typ.kind == tyTypeDesc
+    isTupleType = tupexp[0].typ.kind in {tyTypeDesc, tyGenericParam}
     # check if either everything or nothing is tyTypeDesc
     for i in 1..<tupexp.len:
-      if isTupleType != (tupexp[i].typ.kind == tyTypeDesc):
+      if isTupleType != (tupexp[i].typ.kind in {tyTypeDesc, tyGenericParam}):
         return localErrorNode(c, n, tupexp[i].info, "Mixing types and values in tuples is not allowed.")
   if isTupleType: # expressions as ``(int, string)`` are reinterpret as type expressions
     result = n
diff --git a/tests/tuples/tgenericparamtypetuple.nim b/tests/tuples/tgenericparamtypetuple.nim
new file mode 100644
index 0000000000000..83705fd2dba55
--- /dev/null
+++ b/tests/tuples/tgenericparamtypetuple.nim
@@ -0,0 +1,25 @@
+# issue #25312
+
+import heapqueue
+
+proc test1[T](test: (float, T)) = # Works
+    discard
+
+proc test2[T](test: seq[(float, T)]) = # Works
+    discard
+
+proc test3[T](test: HeapQueue[tuple[sqd: float, data: T]]) = # Works
+    discard
+
+proc test4(test: HeapQueue[(float, float)]) = # Works
+    discard
+
+type ExampleObj = object
+    a: string
+    b: seq[float]
+
+proc test5(test: HeapQueue[(float, ExampleObj)]) = # Works
+    discard
+
+proc failingTest[T](test: HeapQueue[(float, T)]) = # (Compile) Error: Mixing types and values in tuples is not allowed.
+    discard

From 65090150a2b869ca6f6b1e5a5a3f115fb89a1f35 Mon Sep 17 00:00:00 2001
From: metagn <metagngn@gmail.com>
Date: Tue, 25 Nov 2025 20:54:00 +0300
Subject: [PATCH 2/3] add more tests

---
 tests/tuples/tgenericparamtypetuple.nim | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tests/tuples/tgenericparamtypetuple.nim b/tests/tuples/tgenericparamtypetuple.nim
index 83705fd2dba55..93f1ff2d29a66 100644
--- a/tests/tuples/tgenericparamtypetuple.nim
+++ b/tests/tuples/tgenericparamtypetuple.nim
@@ -23,3 +23,12 @@ proc test5(test: HeapQueue[(float, ExampleObj)]) = # Works
 
 proc failingTest[T](test: HeapQueue[(float, T)]) = # (Compile) Error: Mixing types and values in tuples is not allowed.
     discard
+
+proc failingTest2[T](test: HeapQueue[(T, float)]) = # (Compile) Error: Mixing types and values in tuples is not allowed.
+    discard
+
+proc test6[T](test: HeapQueue[(T, T)]) = # works
+    discard
+
+proc test7[T, U](test: HeapQueue[(T, U)]) = # works
+    discard

From e490b9aeabc696057bddd08f50c61f06c56d44b9 Mon Sep 17 00:00:00 2001
From: metagn <metagngn@gmail.com>
Date: Tue, 25 Nov 2025 21:39:54 +0300
Subject: [PATCH 3/3] slightly better check but still not great

---
 compiler/semexprs.nim | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index b74d1adc66efc..8384e514b0d34 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -3054,6 +3054,13 @@ proc semExport(c: PContext, n: PNode): PNode =
 
         s = nextOverloadIter(o, c, a)
 
+proc isTypeTupleField(n: PNode): bool {.inline.} =
+  result = n.typ.kind == tyTypeDesc or
+    (n.typ.kind == tyGenericParam and n.typ.sym.kind == skGenericParam)
+    # `skGenericParam` stays as `tyGenericParam` type rather than being wrapped in `tyTypeDesc`
+    # would check if `n` itself is an `skGenericParam` symbol, but these symbols semcheck to an ident
+    # maybe check if `n` is an ident to ensure this is not a value with the generic param type?
+
 proc semTupleConstr(c: PContext, n: PNode, flags: TExprFlags; expectedType: PType = nil): PNode =
   result = semTuplePositionsConstr(c, n, flags, expectedType)
   if result.typ.kind == tyFromExpr:
@@ -3064,10 +3071,10 @@ proc semTupleConstr(c: PContext, n: PNode, flags: TExprFlags; expectedType: PTyp
   var isTupleType: bool = false
   if tupexp.len > 0: # don't interpret () as type
     internalAssert c.config, tupexp.kind == nkTupleConstr
-    isTupleType = tupexp[0].typ.kind in {tyTypeDesc, tyGenericParam}
+    isTupleType = isTypeTupleField(tupexp[0])
     # check if either everything or nothing is tyTypeDesc
     for i in 1..<tupexp.len:
-      if isTupleType != (tupexp[i].typ.kind in {tyTypeDesc, tyGenericParam}):
+      if isTupleType != isTypeTupleField(tupexp[i]):
         return localErrorNode(c, n, tupexp[i].info, "Mixing types and values in tuples is not allowed.")
   if isTupleType: # expressions as ``(int, string)`` are reinterpret as type expressions
     result = n