breaking change: 'and' and 'mod' do not produce a subrange type anymore; fixes #5854

changelog.md

@@ -28,3 +28,6 @@
   take ``BackwardsIndex`` indices. ``BackwardsIndex`` is produced by ``system.^``.
   This means if you overload ``[]`` or ``[]=`` you need to ensure they also work
   with ``system.BackwardsIndex`` (if applicable for the accessors).
+- ``mod`` and bitwise ``and`` do not produce ``range`` subtypes anymore. This
+  turned out to be more harmful than helpful and the language is simpler
+  without this special typing rule.

compiler/semexprs.nim

@@ -550,7 +550,6 @@ proc evalAtCompileTime(c: PContext, n: PNode): PNode =
       result = semfold.getConstExpr(c.module, call)
       if result.isNil: result = n
       else: return result
-    result.typ = semfold.getIntervalType(callee.magic, call)
 
   block maybeLabelAsStatic:
     # XXX: temporary work-around needed for tlateboundstatic.

compiler/semfold.nim

@@ -137,116 +137,6 @@ proc makeRangeF(typ: PType, first, last: BiggestFloat): PType =
   result.n = n
   addSonSkipIntLit(result, skipTypes(typ, {tyRange}))
 
-proc getIntervalType*(m: TMagic, n: PNode): PType =
-  # Nim requires interval arithmetic for ``range`` types. Lots of tedious
-  # work but the feature is very nice for reducing explicit conversions.
-  const ordIntLit = {nkIntLit..nkUInt64Lit}
-  result = n.typ
-
-  template commutativeOp(opr: untyped) =
-    let a = n.sons[1]
-    let b = n.sons[2]
-    if isIntRangeOrLit(a.typ) and isIntRangeOrLit(b.typ):
-      result = makeRange(pickIntRange(a.typ, b.typ),
-                         opr(pickMinInt(a), pickMinInt(b)),
-                         opr(pickMaxInt(a), pickMaxInt(b)))
-
-  template binaryOp(opr: untyped) =
-    let a = n.sons[1]
-    let b = n.sons[2]
-    if isIntRange(a.typ) and b.kind in {nkIntLit..nkUInt64Lit}:
-      result = makeRange(a.typ,
-                         opr(pickMinInt(a), pickMinInt(b)),
-                         opr(pickMaxInt(a), pickMaxInt(b)))
-
-  case m
-  of mUnaryMinusI, mUnaryMinusI64:
-    let a = n.sons[1].typ
-    if isIntRange(a):
-      # (1..3) * (-1) == (-3.. -1)
-      result = makeRange(a, 0|-|lastOrd(a), 0|-|firstOrd(a))
-  of mUnaryMinusF64:
-    let a = n.sons[1].typ
-    if isFloatRange(a):
-      result = makeRangeF(a, -getFloat(a.n.sons[1]),
-                             -getFloat(a.n.sons[0]))
-  of mAbsF64:
-    let a = n.sons[1].typ
-    if isFloatRange(a):
-      # abs(-5.. 1) == (1..5)
-      if a.n[0].floatVal <= 0.0:
-        result = makeRangeF(a, 0.0, abs(getFloat(a.n.sons[0])))
-      else:
-        result = makeRangeF(a, abs(getFloat(a.n.sons[1])),
-                               abs(getFloat(a.n.sons[0])))
-  of mAbsI:
-    let a = n.sons[1].typ
-    if isIntRange(a):
-      if a.n[0].intVal <= 0:
-        result = makeRange(a, 0, `|abs|`(getInt(a.n.sons[0])))
-      else:
-        result = makeRange(a, `|abs|`(getInt(a.n.sons[1])),
-                              `|abs|`(getInt(a.n.sons[0])))
-  of mSucc:
-    let a = n.sons[1].typ
-    let b = n.sons[2].typ
-    if isIntRange(a) and isIntLit(b):
-      # (-5.. 1) + 6 == (-5 + 6)..(-1 + 6)
-      result = makeRange(a, pickMinInt(n.sons[1]) |+| pickMinInt(n.sons[2]),
-                            pickMaxInt(n.sons[1]) |+| pickMaxInt(n.sons[2]))
-  of mPred:
-    let a = n.sons[1].typ
-    let b = n.sons[2].typ
-    if isIntRange(a) and isIntLit(b):
-      result = makeRange(a, pickMinInt(n.sons[1]) |-| pickMinInt(n.sons[2]),
-                            pickMaxInt(n.sons[1]) |-| pickMaxInt(n.sons[2]))
-  of mAddI, mAddU:
-    commutativeOp(`|+|`)
-  of mMulI, mMulU:
-    commutativeOp(`|*|`)
-  of mSubI, mSubU:
-    binaryOp(`|-|`)
-  of mBitandI:
-    # since uint64 is still not even valid for 'range' (since it's no ordinal
-    # yet), we exclude it from the list (see bug #1638) for now:
-    var a = n.sons[1]
-    var b = n.sons[2]
-    # symmetrical:
-    if b.kind notin ordIntLit: swap(a, b)
-    if b.kind in ordIntLit:
-      let x = b.intVal|+|1
-      if (x and -x) == x and x >= 0:
-        result = makeRange(n.typ, 0, b.intVal)
-  of mModU:
-    let a = n.sons[1]
-    let b = n.sons[2]
-    if b.kind in ordIntLit:
-      if b.intVal >= 0:
-        result = makeRange(n.typ, 0, b.intVal-1)
-      else:
-        result = makeRange(n.typ, b.intVal+1, 0)
-  of mModI:
-    # so ... if you ever wondered about modulo's signedness; this defines it:
-    let a = n.sons[1]
-    let b = n.sons[2]
-    if b.kind in {nkIntLit..nkUInt64Lit}:
-      if b.intVal >= 0:
-        result = makeRange(n.typ, -(b.intVal-1), b.intVal-1)
-      else:
-        result = makeRange(n.typ, b.intVal+1, -(b.intVal+1))
-  of mDivI, mDivU:
-    binaryOp(`|div|`)
-  of mMinI:
-    commutativeOp(min)
-  of mMaxI:
-    commutativeOp(max)
-  else: discard
-
-discard """
-  mShlI,
-  mShrI, mAddF64, mSubF64, mMulF64, mDivF64, mMaxF64, mMinF64
-"""
-
 proc evalIs(n, a: PNode): PNode =
   # XXX: This should use the standard isOpImpl
   internalAssert a.kind == nkSym and a.sym.kind == skType

doc/manual/types.txt

@@ -137,25 +137,6 @@ determined). Assignments from the base type to one of its subrange types
 
 A subrange type has the same size as its base type (``int`` in the example).
 
-Nim requires `interval arithmetic`:idx: for subrange types over a set
-of built-in operators that involve constants: ``x %% 3`` is of
-type ``range[0..2]``. The following built-in operators for integers are
-affected by this rule: ``-``, ``+``, ``*``, ``min``, ``max``, ``succ``,
-``pred``, ``mod``, ``div``, ``%%``, ``and`` (bitwise ``and``).
-
-Bitwise ``and`` only produces a ``range`` if one of its operands is a
-constant *x* so that (x+1) is a power of two.
-(Bitwise ``and`` is then a ``%%`` operation.)
-
-This means that the following code is accepted:
-
-.. code-block:: nim
-  case (x and 3) + 7
-  of 7: echo "A"
-  of 8: echo "B"
-  of 9: echo "C"
-  of 10: echo "D"
-  # note: no ``else`` required as (x and 3) + 7 has the type: range[7..10]
 
 
 Pre-defined floating point types

tests/arithm/tsubrange.nim

@@ -0,0 +1,13 @@
+discard """
+  output: '''1'''
+"""
+
+# bug #5854
+type
+  n16* = range[0'i16..high(int16)]
+
+var level: n16 = 1
+let maxLevel: n16 = 1
+
+level = min(level + 2, maxLevel)
+echo level

todo.txt

@@ -2,7 +2,6 @@ version 1.0 battle plan
 =======================
 
 - make FlowVar compatible to Futures
-- remove 'mod x' type rule
 - fix "high priority" bugs
 - try to fix as many compiler crashes as reasonable