Hrm, the new errors highlighted some code that seems to be broken

New issue: since `Table[A, B]` allocates its backing storage with
`newSeq[KeyValuePair[A, B]]`, it's no longer legal to create a table
with `not nil` types used as either keys or values.

lib/pure/collections/sequtils.nim

@@ -371,9 +371,8 @@ proc map*[T, S](s: openArray[T], op: proc (x: T): S {.closure.}):
       b = map(a, proc(x: int): string = $x)
     assert b == @["1", "2", "3", "4"]
 
-  newSeq(result, s.len)
-  for i in 0 ..< s.len:
-    result[i] = op(s[i])
+  result = newSeqOfCap[S](s.len)
+  for elem in s: result.add op(elem)
 
 proc apply*[T](s: var openArray[T], op: proc (x: var T) {.closure.})
                                                               {.inline.} =

lib/pure/collections/sharedtables.nim

@@ -77,8 +77,7 @@ template withValue*[A, B](t: var SharedTable[A, B], key: A,
   try:
     var hc: Hash
     var index = rawGet(t, key, hc)
-    let hasKey = index >= 0
-    if hasKey:
+    if index >= 0:
       var value {.inject.} = addr(t.data[index].val)
       body
   finally:
@@ -104,8 +103,7 @@ template withValue*[A, B](t: var SharedTable[A, B], key: A,
   try:
     var hc: Hash
     var index = rawGet(t, key, hc)
-    let hasKey = index >= 0
-    if hasKey:
+    if index >= 0:
       var value {.inject.} = addr(t.data[index].val)
       body1
     else:
@@ -119,13 +117,13 @@ proc mget*[A, B](t: var SharedTable[A, B], key: A): var B =
   withLock t:
     var hc: Hash
     var index = rawGet(t, key, hc)
-    let hasKey = index >= 0
-    if hasKey: result = t.data[index].val
-  if not hasKey:
-    when compiles($key):
-      raise newException(KeyError, "key not found: " & $key)
+    if index >= 0:
+      result = t.data[index].val
     else:
-      raise newException(KeyError, "key not found")
+      when compiles($key):
+        raise newException(KeyError, "key not found: " & $key)
+      else:
+        raise newException(KeyError, "key not found")
 
 proc mgetOrPut*[A, B](t: var SharedTable[A, B], key: A, val: B): var B =
   ## retrieves value at ``t[key]`` or puts ``val`` if not present, either way

lib/pure/ioselects/ioselectors_epoll.nim

@@ -502,8 +502,7 @@ proc contains*[T](s: Selector[T], fd: SocketHandle|int): bool {.inline.} =
 proc getData*[T](s: Selector[T], fd: SocketHandle|int): var T =
   let fdi = int(fd)
   s.checkFd(fdi)
-  if fdi in s:
-    result = s.fds[fdi].data
+  result = s.fds[fdi].data
 
 proc setData*[T](s: Selector[T], fd: SocketHandle|int, data: T): bool =
   let fdi = int(fd)

lib/pure/ioselects/ioselectors_kqueue.nim

@@ -600,8 +600,7 @@ proc contains*[T](s: Selector[T], fd: SocketHandle|int): bool {.inline.} =
 proc getData*[T](s: Selector[T], fd: SocketHandle|int): var T =
   let fdi = int(fd)
   s.checkFd(fdi)
-  if fdi in s:
-    result = s.fds[fdi].data
+  result = s.fds[fdi].data
 
 proc setData*[T](s: Selector[T], fd: SocketHandle|int, data: T): bool =
   let fdi = int(fd)

lib/pure/ioselects/ioselectors_select.nim

@@ -410,11 +410,17 @@ else:
     body
 
 proc getData*[T](s: Selector[T], fd: SocketHandle|int): var T =
+  # The compiler needs this to prove that all code paths return a value
+  result = (cast[ptr T](0'u))[]
+
   s.withSelectLock():
     let fdi = int(fd)
     for i in 0..<FD_SETSIZE:
       if s.fds[i].ident == fdi:
-        return s.fds[i].data
+        result = s.fds[i].data
+        break
+
+  assert cast[uint](addr(result)) != 0
 
 proc setData*[T](s: Selector[T], fd: SocketHandle|int, data: T): bool =
   s.withSelectLock():

lib/pure/parsecsv.nim

@@ -338,8 +338,8 @@ proc rowEntry*(my: var CsvParser, entry: string): var string =
     strm.close()
 
   let index = my.headers.find(entry)
-  if index >= 0:
-    result = my.row[index]
+  assert index >= 0
+  result = my.row[index]
 
 when not defined(testing) and isMainModule:
   import os

tests/collections/ttables.nim

@@ -80,7 +80,7 @@ block thashes:
   # Test with range
   block:
     type
-      R = range[1..10]
+      R = range[0..9]
     var t = initTable[R,int]() # causes warning, why?
     t[1] = 42 # causes warning, why?
     t[2] = t[1] + 1

tests/discard/tneedsdiscard_in_for.nim

@@ -8,7 +8,7 @@ type
   Rgba8 = object
 
 proc premultiply*(c: var Rgba8): var Rgba8 =
-  discard
+  return c
 
 type
   App = ref object