minor code cleanups (#21215)

lib/std/enumerate.nim

@@ -21,7 +21,7 @@ macro enumerate*(x: ForLoopStmt): untyped {.since: (1, 3).} =
   ## The default starting count `0` can be manually overridden if needed.
   runnableExamples:
     let a = [10, 20, 30]
-    var b: seq[(int, int)]
+    var b: seq[(int, int)] = @[]
     for i, x in enumerate(a):
       b.add((i, x))
     assert b == @[(0, 10), (1, 20), (2, 30)]

lib/std/enumutils.nim

@@ -112,9 +112,9 @@ const invalidSlot = uint8.high
 
 proc genLookup[T: typedesc[HoleyEnum]](_: T): auto =
   const n = span(T)
-  var ret: array[n, uint8]
   var i = 0
   assert n <= invalidSlot.int
+  var ret {.noinit.}: array[n, uint8]
   for ai in mitems(ret): ai = invalidSlot
   for ai in items(T):
     ret[ai.ord - T.low.ord] = uint8(i)

lib/std/envvars.nim

@@ -94,8 +94,10 @@ when not defined(nimscript):
         assert getEnv("unknownEnv", "doesn't exist") == "doesn't exist"
 
       let env = getEnvImpl(key)
-      if env == nil: return default
-      result = $env
+      if env == nil:
+        result = default
+      else:
+        result = $env
 
     proc existsEnv*(key: string): bool {.tags: [ReadEnvEffect].} =
       ## Checks whether the environment variable named `key` exists.
@@ -109,7 +111,7 @@ when not defined(nimscript):
       runnableExamples:
         assert not existsEnv("unknownEnv")
 
-      return getEnvImpl(key) != nil
+      result = getEnvImpl(key) != nil
 
     proc putEnv*(key, val: string) {.tags: [WriteEnvEffect].} =
       ## Sets the value of the `environment variable`:idx: named `key` to `val`.
@@ -140,7 +142,7 @@ when not defined(nimscript):
       ## * `envPairs iterator`_
       template bail = raiseOSError(osLastError(), key)
       when defined(windows):
-        #[ 
+        #[
         # https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/putenv-s-wputenv-s?view=msvc-160
         > You can remove a variable from the environment by specifying an empty string (that is, "") for value_string
         note that nil is not legal
@@ -177,20 +179,17 @@ when not defined(nimscript):
 
     iterator envPairsImpl(): tuple[key, value: string] {.tags: [ReadEnvEffect].} =
       when defined(windows):
-        block implBlock:
-          template impl(get_fun, typ, size, zero, free_fun) =
-            let env = get_fun()
-            var e = env
-            if e == nil: break implBlock
-            while true:
-              let eend = strEnd(e)
-              let kv = $e
-              let p = find(kv, '=')
-              yield (substr(kv, 0, p-1), substr(kv, p+1))
-              e = cast[typ](cast[int](eend)+size)
-              if typeof(zero)(eend[1]) == zero: break
-            discard free_fun(env)
-          impl(getEnvironmentStringsW, WideCString, 2, 0, freeEnvironmentStringsW)
+        let env = getEnvironmentStringsW()
+        var e = env
+        if e != nil:
+          while true:
+            let eend = strEnd(e)
+            let kv = $e
+            let p = find(kv, '=')
+            yield (substr(kv, 0, p-1), substr(kv, p+1))
+            e = cast[WideCString](cast[ByteAddress](eend)+2)
+            if int(eend[1]) == 0: break
+          discard freeEnvironmentStringsW(env)
       else:
         var i = 0
         when defined(macosx) and not defined(ios) and not defined(emscripten):

lib/std/oserrors.nim

@@ -75,17 +75,14 @@ proc newOSError*(
   ## See also:
   ## * `osErrorMsg proc`_
   ## * `osLastError proc`_
-  var e: owned(ref OSError); new(e)
-  e.errorCode = errorCode.int32
-  e.msg = osErrorMsg(errorCode)
+  result = (ref OSError)(errorCode: errorCode.int32, msg: osErrorMsg(errorCode))
   if additionalInfo.len > 0:
-    if e.msg.len > 0 and e.msg[^1] != '\n': e.msg.add '\n'
-    e.msg.add "Additional info: "
-    e.msg.add additionalInfo
+    if result.msg.len > 0 and result.msg[^1] != '\n': result.msg.add '\n'
+    result.msg.add "Additional info: "
+    result.msg.add additionalInfo
       # don't add trailing `.` etc, which negatively impacts "jump to file" in IDEs.
-  if e.msg == "":
-    e.msg = "unknown OS error"
-  return e
+  if result.msg == "":
+    result.msg = "unknown OS error"
 
 proc raiseOSError*(errorCode: OSErrorCode, additionalInfo = "") {.noinline.} =
   ## Raises an `OSError exception <system.html#OSError>`_.