fix: var a{.foo.} = expr inside templates (refs #15920) (except when foo is overloaded) (#13869)

* fix: `var a{.foo.} = expr` inside templates
* add test
* improve tdecls test
* improve tests
* add failing test
* PRTEMP
* fixup

tests/stdlib/tdecls.nim

@@ -1,6 +1,10 @@
+discard """
+  targets: "c cpp js"
+"""
+
 import std/decls
 
-block:
+template fun() =
   var s = @[10,11,12]
   var a {.byaddr.} = s[0]
   a+=100
@@ -34,6 +38,13 @@ block:
   doAssert compiles(block:
     var b2 {.byaddr.}: int = s[2])
 
+proc fun2() = fun()
+fun()
+fun2()
+static: fun2()
+when false: # pending bug #13887
+  static: fun()
+
 ## We can define custom pragmas in user code
 template byUnsafeAddr(lhs, typ, expr) =
   when typ is type(nil):
@@ -68,3 +79,13 @@ block: # nkAccQuoted
     let a {.`cast`.} = s[0]
     doAssert a == "foo"
     doAssert a[0].unsafeAddr == s[0][0].unsafeAddr
+
+block: # bug #15920
+  template foo(lhs, typ, expr) =
+    let lhs = expr
+  proc fun1()=
+    let a {.foo.} = 1
+  template fun2()=
+    let a {.foo.} = 1
+  fun1() # ok
+  fun2() # BUG

tests/stdlib/tsince.nim

@@ -27,6 +27,6 @@ since (99, 3):
   doAssert false
 
 when false:
-  # pending https://github.com/timotheecour/Nim/issues/129
+  # pending bug #15920
   # Error: cannot attach a custom pragma to 'fun3'
   template fun3(): int {.since: (1, 3).} = 12