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/pragmas/tpragmas_misc.nim

@@ -10,3 +10,55 @@ block:
   static: doAssert defined(tpragmas_misc_def)
   {.undef(tpragmas_misc_def).}
   static: doAssert not defined(tpragmas_misc_def)
+
+block: # (partial fix) bug #15920
+  block: # var template pragmas don't work in templates
+    template foo(lhs, typ, expr) =
+      let lhs = expr
+    proc fun1()=
+      let a {.foo.} = 1
+    template fun2()=
+      let a {.foo.} = 1
+    fun1() # ok
+    fun2() # WAS bug
+
+  template foo2() = discard # distractor (template or other symbol kind)
+  block:
+    template foo2(lhs, typ, expr) =
+      let lhs = expr
+    proc fun1()=
+      let a {.foo2.} = 1
+    template fun2()=
+      let a {.foo2.} = 1
+    fun1() # ok
+    when false: # bug: Error: invalid pragma: foo2
+      fun2()
+
+  block: # proc template pragmas don't work in templates
+    # adapted from $nim/lib/std/private/since.nim
+    # case without overload
+    template since3(version: (int, int), body: untyped) {.dirty.} =
+      when (NimMajor, NimMinor) >= version:
+        body
+    when false: # bug
+      template fun3(): int {.since3: (1, 3).} = 12
+
+  block: # ditto, w
+    # case with overload
+    template since2(version: (int, int), body: untyped) {.dirty.} =
+      when (NimMajor, NimMinor) >= version:
+        body
+    template since2(version: (int, int, int), body: untyped) {.dirty.} =
+      when (NimMajor, NimMinor, NimPatch) >= version:
+        body
+    when false: # bug
+      template fun3(): int {.since2: (1, 3).} = 12
+
+when true: # D20210801T100514:here
+  from macros import genSym
+  block:
+    template fn() =
+      var ret {.gensym.}: int # must special case template pragmas so it doesn't get confused
+      discard ret
+    fn()
+    static: discard genSym()