From f2e4ae0016ff0a344e814238ffc26146ab765f21 Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Wed, 6 May 2026 14:42:36 +0800
Subject: [PATCH] fixes lent tuple codegen error (#25782)

ref https://github.com/nim-lang/Nim/pull/25783

This pull request addresses an issue with addressability of tuple
elements of type `lent` or `var` in Nim, ensuring that expressions
involving these types are handled correctly during type changes. The
main changes introduce a check to prevent attempting to change the type
of tuple elements that are views (`var` or `lent`), and a new test is
added to verify the correct error is raised when trying to take the
address of such elements.

Type system and semantic analysis improvements:

* Added the `isViewTarget` template in `semexprs.nim` to check if a type
is a view (`var` or `lent`), and updated `changeType` to skip type
changes for tuple elements that are views. This prevents invalid
addressability operations on these types.
[[1]](diffhunk://#diff-539da3a63df08fa987f1b0c67d26cdc690753843d110b6bf0805a685eeaffd40R655-R657)
[[2]](diffhunk://#diff-539da3a63df08fa987f1b0c67d26cdc690753843d110b6bf0805a685eeaffd40R686-R693)

Testing:

* Added a new test `tlent_tuple_address.nim` to verify that attempting
to take the address of tuple elements of type `lent` correctly produces
an "expression has no address" error.
---
 compiler/semexprs.nim              | 13 ++++++++++---
 tests/lent/tlent_tuple_address.nim | 12 ++++++++++++
 2 files changed, 22 insertions(+), 3 deletions(-)
 create mode 100644 tests/lent/tlent_tuple_address.nim

diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index 64a8d2a4f9..aa0489cd22 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -652,6 +652,9 @@ proc overloadedCallOpr(c: PContext, n: PNode): PNode =
     result = semExpr(c, result, flags = {efNoUndeclared})
 
 proc changeType(c: PContext; n: PNode, newType: PType, check: bool) =
+  template isViewTarget(t: PType): bool =
+    t.skipTypes({tyGenericInst, tyAlias, tySink}).kind in {tyVar, tyLent}
+
   case n.kind
   of nkCurly:
     for i in 0..<n.len:
@@ -680,12 +683,15 @@ proc changeType(c: PContext; n: PNode, newType: PType, check: bool) =
           if f == nil:
             globalError(c.config, m.info, "unknown identifier: " & m.sym.name.s)
             return
-          changeType(c, n[i][1], f.typ, check)
+          if not isViewTarget(f.typ):
+            changeType(c, n[i][1], f.typ, check)
         else:
-          changeType(c, n[i][1], tup[i], check)
+          if not isViewTarget(tup[i]):
+            changeType(c, n[i][1], tup[i], check)
     else:
       for i in 0..<n.len:
-        changeType(c, n[i], tup[i], check)
+        if not isViewTarget(tup[i]):
+          changeType(c, n[i], tup[i], check)
         when false:
           var m = n[i]
           var a = newNodeIT(nkExprColonExpr, m.info, newType[i])
@@ -708,6 +714,7 @@ proc changeType(c: PContext; n: PNode, newType: PType, check: bool) =
         localError(c.config, n.info, "cannot convert '" & n.sym.name.s &
                                          "' to '" & typeNameAndDesc(newType) & "'")
   else: discard
+
   n.typ = newType
 
 proc arrayConstrType(c: PContext, n: PNode): PType =
diff --git a/tests/lent/tlent_tuple_address.nim b/tests/lent/tlent_tuple_address.nim
new file mode 100644
index 0000000000..f9c8d4542d
--- /dev/null
+++ b/tests/lent/tlent_tuple_address.nim
@@ -0,0 +1,12 @@
+discard """
+  errormsg: "expression has no address"
+"""
+
+iterator foo(x: int): (lent int, lent int) =
+  yield (x, x + 1)
+
+
+var x = 12
+for i in foo(x):
+  echo i[0]
+  echo i[1]