evaluate all hidden conversions in case branches (#24187)

fixes #11422, refs #8336/#8333, refs #20130

The compiler generates conversion nodes *after* evaluating the branches
of case statements as constants, the reasoning is that case branches
accept constants of different types, like arrays or sets. But this means
that conversion nodes that need to be evaluated like converter calls
don't get evaluated as a constant for codegen. #8336 fixed this by
re-evaluating the node if an `nkHiddenCallConv` was created, and in
#20130 this logic also had to be added for `nkHiddenStdConv` for
cstrings. This logic was only for single case elements, it has now been
added to range elements as well to fix #11422. Additionally, all
conversion nodes are now evaluated for simplicity, but maybe this won't
pass CI.

compiler/semtypes.nim

@@ -586,9 +586,14 @@ proc semBranchRange(c: PContext, n, a, b: PNode, covered: var Int128): PNode =
   let bc = semConstExpr(c, b)
   if ac.kind in {nkStrLit..nkTripleStrLit} or bc.kind in {nkStrLit..nkTripleStrLit}:
     localError(c.config, b.info, "range of string is invalid")
-  let at = fitNode(c, n[0].typ, ac, ac.info).skipConvTakeType
-  let bt = fitNode(c, n[0].typ, bc, bc.info).skipConvTakeType
-
+  var at = fitNode(c, n[0].typ, ac, ac.info).skipConvTakeType
+  var bt = fitNode(c, n[0].typ, bc, bc.info).skipConvTakeType
+  # the calls to fitNode may introduce calls to converters
+  # mirrored with semCaseBranch for single elements
+  if at.kind in {nkHiddenCallConv, nkHiddenStdConv, nkHiddenSubConv}:
+    at = semConstExpr(c, at)
+  if bt.kind in {nkHiddenCallConv, nkHiddenStdConv, nkHiddenSubConv}:
+    bt = semConstExpr(c, bt)
   result = newNodeI(nkRange, a.info)
   result.add(at)
   result.add(bt)
@@ -636,8 +641,8 @@ proc semCaseBranch(c: PContext, n, branch: PNode, branchIndex: int,
         checkMinSonsLen(n, 1, c.config)
         var tmp = fitNode(c, n[0].typ, r, r.info)
         # the call to fitNode may introduce a call to a converter
-        if tmp.kind == nkHiddenCallConv or
-            (tmp.kind == nkHiddenStdConv and n[0].typ.kind == tyCstring):
+        # mirrored with semBranchRange
+        if tmp.kind in {nkHiddenCallConv, nkHiddenStdConv, nkHiddenSubConv}:
           tmp = semConstExpr(c, tmp)
         branch[i] = skipConv(tmp)
         inc(covered)

tests/casestmt/tcasestmt.nim

@@ -41,6 +41,11 @@ block t8333:
   case 0
   of 'a': echo 0
   else: echo 1
+block: # issue #11422
+  var c: int = 5
+  case c
+  of 'a' .. 'c': discard
+  else: discard
 
 
 block emptyset_when: