From 7ccc7d7e93e0fdfcf72aed239cf8b5d4c04e7de5 Mon Sep 17 00:00:00 2001
From: Andreas Rumpf <rumpf_a@web.de>
Date: Sat, 30 May 2020 15:32:31 +0200
Subject: [PATCH] fixes #14498 [backport:1.2] (#14503)

---
 compiler/parampatterns.nim        | 12 +++++++++---
 compiler/semexprs.nim             |  2 +-
 tests/lent/tnot_allowed_lent.nim  |  4 ++--
 tests/lent/tnot_allowed_lent2.nim | 14 ++++++++++++++
 4 files changed, 26 insertions(+), 6 deletions(-)
 create mode 100644 tests/lent/tnot_allowed_lent2.nim

diff --git a/compiler/parampatterns.nim b/compiler/parampatterns.nim
index 486f8ff544..33881a7b30 100644
--- a/compiler/parampatterns.nim
+++ b/compiler/parampatterns.nim
@@ -176,6 +176,7 @@ type
     arLocalLValue,            # is an l-value, but local var; must not escape
                               # its stack frame!
     arDiscriminant,           # is a discriminant
+    arLentValue,              # lent value
     arStrange                 # it is a strange beast like 'typedesc[var T]'
 
 proc exprRoot*(n: PNode): PSym =
@@ -260,9 +261,14 @@ proc isAssignable*(owner: PSym, n: PNode; isUnsafeAddr=false): TAssignableResult
       # types that are equal modulo distinction preserve l-value:
       result = isAssignable(owner, n[1], isUnsafeAddr)
   of nkHiddenDeref:
-    if isUnsafeAddr and n[0].typ.kind == tyLent: result = arLValue
-    elif n[0].typ.kind == tyLent: result = arDiscriminant
-    else: result = arLValue
+    let n0 = n[0]
+    if n0.typ.kind == tyLent:
+      if isUnsafeAddr or (n0.kind == nkSym and n0.sym.kind == skResult):
+        result = arLValue
+      else:
+        result = arLentValue
+    else:
+      result = arLValue
   of nkDerefExpr, nkHiddenAddr:
     result = arLValue
   of nkObjUpConv, nkObjDownConv, nkCheckedFieldExpr:
diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index e29101385e..c5b864d1fb 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -1712,7 +1712,7 @@ proc semAsgn(c: PContext, n: PNode; mode=asgnNormal): PNode =
   if le == nil:
     localError(c.config, a.info, "expression has no type")
   elif (skipTypes(le, {tyGenericInst, tyAlias, tySink}).kind != tyVar and
-        isAssignable(c, a) == arNone) or
+        isAssignable(c, a) in {arNone, arLentValue}) or
       skipTypes(le, abstractVar).kind in {tyOpenArray, tyVarargs}:
     # Direct assignment to a discriminant is allowed!
     localError(c.config, a.info, errXCannotBeAssignedTo %
diff --git a/tests/lent/tnot_allowed_lent.nim b/tests/lent/tnot_allowed_lent.nim
index b144ce36b8..2de18d4afa 100644
--- a/tests/lent/tnot_allowed_lent.nim
+++ b/tests/lent/tnot_allowed_lent.nim
@@ -7,10 +7,10 @@ type
 
 proc mytest1(s: MyObject, i: int): lent string =
   ## works fine
-  if i < s.x.len - 1 and s.x[i] != "": 
+  if i < s.x.len - 1 and s.x[i] != "":
     result = s.x[i]
   else: raise newException(KeyError, "err1")
-  
+
 proc mytest2(s: MyObject, i: int): lent string =
   ## reject due to if expr
   if i < s.x.len - 1 and s.x[i] != "": s.x[i]
diff --git a/tests/lent/tnot_allowed_lent2.nim b/tests/lent/tnot_allowed_lent2.nim
new file mode 100644
index 0000000000..e61cae9227
--- /dev/null
+++ b/tests/lent/tnot_allowed_lent2.nim
@@ -0,0 +1,14 @@
+discard """
+  errmsg: "'x' cannot be assigned to"
+  line: 10
+"""
+
+proc bug14498 =
+  var a = @['a', 'b', 'c', 'd', 'e', 'f']
+
+  for x in a:
+    x = 'c'
+
+  echo a
+
+bug14498()