sink parameter inference for types that have destructors (#13544)

* ensure capitalize doesn't take an inferred sink parameter

* sink parameter inference: first version, for now disabled. Changed that sink parameters can be consumed multiple times in order to adhere to our spec.

* sink inference can now be disabled with .nosinks; sometimes for proc type interop this is required

* fixes yet another critical DFA bug

* better implementation that also understands if expressions etc

* document sink parameter inference and allow for global disabling

compiler/ast.nim

@@ -229,7 +229,7 @@ type
   TNodeKinds* = set[TNodeKind]
 
 type
-  TSymFlag* = enum    # 40 flags!
+  TSymFlag* = enum    # 41 flags!
     sfUsed,           # read access of sym (for warnings) or simply used
     sfExported,       # symbol is exported from module
     sfFromGeneric,    # symbol is instantiation of a generic; this is needed
@@ -238,6 +238,8 @@ type
     sfGlobal,         # symbol is at global scope
 
     sfForward,        # symbol is forward declared
+    sfWasForwarded,   # symbol had a forward declaration
+                      # (implies it's too dangerous to patch its type signature)
     sfImportc,        # symbol is external; imported
     sfExportc,        # symbol is exported (under a specified name)
     sfMangleCpp,      # mangle as cpp (combines with `sfExportc`)
@@ -847,7 +849,7 @@ type
     position*: int            # used for many different things:
                               # for enum fields its position;
                               # for fields its offset
-                              # for parameters its position
+                              # for parameters its position (starting with 0)
                               # for a conditional:
                               # 1 iff the symbol is defined, else 0
                               # (or not in symbol table)
@@ -1865,6 +1867,9 @@ proc isInlineIterator*(typ: PType): bool {.inline.} =
 proc isClosureIterator*(typ: PType): bool {.inline.} =
   typ.kind == tyProc and tfIterator in typ.flags and typ.callConv == ccClosure
 
+proc isClosure*(typ: PType): bool {.inline.} =
+  typ.kind == tyProc and typ.callConv == ccClosure
+
 proc isSinkParam*(s: PSym): bool {.inline.} =
   s.kind == skParam and (s.typ.kind == tySink or tfHasOwned in s.typ.flags)