Fixes #1642.

compiler/ccgexprs.nim

@@ -2095,14 +2095,18 @@ proc expr(p: BProc, n: PNode, d: var TLoc) =
       # due to a bug/limitation in the lambda lifting, unused inner procs
       # are not transformed correctly. We work around this issue (#411) here
       # by ensuring it's no inner proc (owner is a module):
-      if prc.skipGenericOwner.kind == skModule:
+      #
+      # We also check whether the proc captures its environment here to
+      # prevent issue #1642.
+      if prc.skipGenericOwner.kind == skModule and
+         tfCapturesEnv in prc.typ.flags:
         if (optDeadCodeElim notin gGlobalOptions and
             sfDeadCodeElim notin getModule(prc).flags) or
             ({sfExportc, sfCompilerProc} * prc.flags == {sfExportc}) or
             (sfExportc in prc.flags and lfExportLib in prc.loc.flags) or
             (prc.kind == skMethod): 
           # we have not only the header: 
-          if prc.getBody.kind != nkEmpty or lfDynamicLib in prc.loc.flags: 
+          if prc.getBody.kind != nkEmpty or lfDynamicLib in prc.loc.flags:
             genProc(p.module, prc)
   of nkParForStmt: genParForStmt(p, n)
   of nkState: genState(p, n)

tests/closure/tissue1642.nim

@@ -0,0 +1,6 @@
+discard """
+  file: "tissue1642.nim"
+"""
+block:
+  var i = 0
+  proc p() = inc(i)