Fix #8473 (#15169)

* Make explicit {.nimcall.} a seperate calling convention

* Add testcase for #5688

* Fix bootstrapping

* Remove little lies :)

* Use typeflag instead

tests/closure/tinvalidclosure.nim

@@ -1,5 +1,5 @@
 discard """
-  errormsg: "type mismatch: got <proc (x: int){.gcsafe, locks: 0.}>"
+  errormsg: "type mismatch: got <proc (x: int){.nimcall, gcsafe, locks: 0.}>"
   line: 12
 """
 

tests/closure/tinvalidclosure4.nim

@@ -0,0 +1,9 @@
+discard """
+  errormsg: "illegal capture 'v'"
+  line: 7
+"""
+
+proc outer(v: int) =
+  proc b {.nimcall.} = echo v
+  b()
+outer(5)

tests/closure/tinvalidclosure5.nim

@@ -0,0 +1,10 @@
+discard """
+  errormsg: "type mismatch: got <proc (){.closure, gcsafe, locks: 0.}> but expected 'A = proc (){.nimcall.}'"
+  line: 9
+"""
+
+type A = proc() {.nimcall.}
+proc main =
+  let b = 1
+  let a: A = proc() = echo b
+

tests/closure/tnested.nim

@@ -33,6 +33,7 @@ py
 py
 px
 6
+proc (){.closure, gcsafe, locks: 0.}
 '''
 """
 
@@ -177,3 +178,19 @@ block tclosure2:
 
 
     outer2()
+
+# bug #5688
+
+import typetraits
+
+proc myDiscard[T](a: T) = discard
+
+proc foo() =
+  let a = 5
+  let f = (proc() =
+             myDiscard (proc() = echo a)
+          )
+  echo name(type(f))
+
+foo()
+