Use defer in iterator to avoid possible leaks. Fixes #3802

lib/pure/os.nim

@@ -774,6 +774,7 @@ iterator walkFiles*(pattern: string): string {.tags: [ReadDirEffect].} =
       res: int
     res = findFirstFile(pattern, f)
     if res != -1:
+      defer: findClose(res)
       while true:
         if not skipFindData(f) and
             (f.dwFileAttributes and FILE_ATTRIBUTE_DIRECTORY) == 0'i32:
@@ -786,7 +787,6 @@ iterator walkFiles*(pattern: string): string {.tags: [ReadDirEffect].} =
               pattern[dotPos+1] == '*':
             yield splitFile(pattern).dir / extractFilename(ff)
         if findNextFile(res, f) == 0'i32: break
-      findClose(res)
   else: # here we use glob
     var
       f: Glob
@@ -795,11 +795,11 @@ iterator walkFiles*(pattern: string): string {.tags: [ReadDirEffect].} =
     f.gl_pathc = 0
     f.gl_pathv = nil
     res = glob(pattern, 0, nil, addr(f))
+    defer: globfree(addr(f))
     if res == 0:
       for i in 0.. f.gl_pathc - 1:
         assert(f.gl_pathv[i] != nil)
         yield $f.gl_pathv[i]
-    globfree(addr(f))
 
 type
   PathComponent* = enum   ## Enumeration specifying a path component.
@@ -845,6 +845,7 @@ iterator walkDir*(dir: string; relative=false): tuple[kind: PathComponent, path:
       var f: WIN32_FIND_DATA
       var h = findFirstFile(dir / "*", f)
       if h != -1:
+        defer: findClose(h)
         while true:
           var k = pcFile
           if not skipFindData(f):
@@ -856,10 +857,10 @@ iterator walkDir*(dir: string; relative=false): tuple[kind: PathComponent, path:
                      else: dir / extractFilename(getFilename(f))
             yield (k, xx)
           if findNextFile(h, f) == 0'i32: break
-        findClose(h)
     else:
       var d = opendir(dir)
       if d != nil:
+        defer: discard closedir(d)
         while true:
           var x = readdir(d)
           if x == nil: break
@@ -883,7 +884,6 @@ iterator walkDir*(dir: string; relative=false): tuple[kind: PathComponent, path:
             if S_ISDIR(s.st_mode): k = pcDir
             if S_ISLNK(s.st_mode): k = succ(k)
             yield (k, y)
-        discard closedir(d)
 
 iterator walkDirRec*(dir: string, filter={pcFile, pcDir}): string {.
   tags: [ReadDirEffect].} =

lib/system.nim

@@ -2960,9 +2960,9 @@ when not defined(JS): #and not defined(nimscript):
       ##       buffer.add(line.replace("a", "0") & '\x0A')
       ##     writeFile(filename, buffer)
       var f = open(filename, bufSize=8000)
+      defer: close(f)
       var res = TaintedString(newStringOfCap(80))
       while f.readLine(res): yield res
-      close(f)
 
     iterator lines*(f: File): TaintedString {.tags: [ReadIOEffect].} =
       ## Iterate over any line in the file `f`.