make var/pointer types not match if base type has to be converted (#24130)

split again from #24038, fixes
status-im/nimbus-eth2#6554 (comment)

`var`/pointer types are no longer implicitly convertible to each other
if their element types either:

* require an int conversion or another conversion operation as long as
it's not to `openarray`,
* are subtypes with pointer indirection,

Previously any conversion below a subrange match would match if the
element type wasn't a pointer type, then it would error later in
`analyseIfAddressTaken`.

Different from #24038 in that the preview define that made subrange
matches also fail to match is removed for a simpler diff so that it can
be backported.

(cherry picked from commit 1660ddf)

Author: metagn

compiler/sigmatch.nim

@@ -984,9 +984,21 @@ proc inferStaticsInRange(c: var TCandidate,
     doInferStatic(lowerBound, getInt(upperBound) + 1 - lengthOrd(c.c.config, concrete))
 
 template subtypeCheck() =
-  if result <= isSubrange and f.lastSon.skipTypes(abstractInst).kind in {
-      tyRef, tyPtr, tyVar, tyLent, tyOwned}:
+  case result
+  of isIntConv:
     result = isNone
+  of isSubrange:
+    discard # XXX should be isNone with preview define, warnings
+  of isConvertible:
+    if f.lastSon.skipTypes(abstractInst).kind != tyOpenArray:
+      # exclude var openarray which compiler supports
+      result = isNone
+  of isSubtype:
+    if f.lastSon.skipTypes(abstractInst).kind in {
+        tyRef, tyPtr, tyVar, tyLent, tyOwned}:
+      # compiler can't handle subtype conversions with pointer indirection
+      result = isNone
+  else: discard
 
 proc isCovariantPtr(c: var TCandidate, f, a: PType): bool =
   # this proc is always called for a pair of matching types

tests/errmsgs/t22097.nim

@@ -1,9 +1,9 @@
 discard """
-  errormsg: "for a 'var' type a variable needs to be passed; but 'uint16(x)' is immutable"
+  errormsg: "type mismatch: got <uint8>"
 """
 
 proc toUInt16(x: var uint16) =
   discard
 
 var x = uint8(1)
-toUInt16 x
+toUInt16 x

tests/int/twrongexplicitvarconv.nim

@@ -0,0 +1,16 @@
+discard """
+  action: reject
+  nimout: '''
+  but expression 'int(a)' is immutable, not 'var'
+'''
+"""
+
+proc `++`(n: var int) =
+  n += 1
+
+var a: int32 = 15
+
+++int(a) #[tt.Error
+^ type mismatch: got <int>]#
+
+echo a

tests/int/twrongvarconv.nim

@@ -0,0 +1,9 @@
+proc `++`(n: var int) =
+  n += 1
+
+var a: int32 = 15
+
+++a #[tt.Error
+^ type mismatch: got <int32>]#
+
+echo a

tests/overload/mvaruintconv.nim

@@ -0,0 +1,145 @@
+import
+  std/[macros, tables, hashes]
+
+export
+  macros
+
+type
+  FieldDescription* = object
+    name*: NimNode
+    isPublic*: bool
+    isDiscriminator*: bool
+    typ*: NimNode
+    pragmas*: NimNode
+    caseField*: NimNode
+    caseBranch*: NimNode
+
+{.push raises: [].}
+
+func isTuple*(t: NimNode): bool =
+  t.kind == nnkBracketExpr and t[0].kind == nnkSym and eqIdent(t[0], "tuple")
+
+macro isTuple*(T: type): untyped =
+  newLit(isTuple(getType(T)[1]))
+
+proc collectFieldsFromRecList(result: var seq[FieldDescription],
+                              n: NimNode,
+                              parentCaseField: NimNode = nil,
+                              parentCaseBranch: NimNode = nil,
+                              isDiscriminator = false) =
+  case n.kind
+  of nnkRecList:
+    for entry in n:
+      collectFieldsFromRecList result, entry,
+                               parentCaseField, parentCaseBranch
+  of nnkRecWhen:
+    for branch in n:
+      case branch.kind:
+      of nnkElifBranch:
+        collectFieldsFromRecList result, branch[1],
+                                 parentCaseField, parentCaseBranch
+      of nnkElse:
+        collectFieldsFromRecList result, branch[0],
+                                 parentCaseField, parentCaseBranch
+      else:
+        doAssert false
+
+  of nnkRecCase:
+    collectFieldsFromRecList result, n[0],
+                             parentCaseField,
+                             parentCaseBranch,
+                             isDiscriminator = true
+
+    for i in 1 ..< n.len:
+      let branch = n[i]
+      case branch.kind
+      of nnkOfBranch:
+        collectFieldsFromRecList result, branch[^1], n[0], branch
+      of nnkElse:
+        collectFieldsFromRecList result, branch[0], n[0], branch
+      else:
+        doAssert false
+
+  of nnkIdentDefs:
+    let fieldType = n[^2]
+    for i in 0 ..< n.len - 2:
+      var field: FieldDescription
+      field.name = n[i]
+      field.typ = fieldType
+      field.caseField = parentCaseField
+      field.caseBranch = parentCaseBranch
+      field.isDiscriminator = isDiscriminator
+
+      if field.name.kind == nnkPragmaExpr:
+        field.pragmas = field.name[1]
+        field.name = field.name[0]
+
+      if field.name.kind == nnkPostfix:
+        field.isPublic = true
+        field.name = field.name[1]
+
+      result.add field
+
+  of nnkSym:
+    result.add FieldDescription(
+      name: n,
+      typ: getType(n),
+      caseField: parentCaseField,
+      caseBranch: parentCaseBranch,
+      isDiscriminator: isDiscriminator)
+
+  of nnkNilLit, nnkDiscardStmt, nnkCommentStmt, nnkEmpty:
+    discard
+
+  else:
+    doAssert false, "Unexpected nodes in recordFields:\n" & n.treeRepr
+
+proc collectFieldsInHierarchy(result: var seq[FieldDescription],
+                              objectType: NimNode) =
+  var objectType = objectType
+
+  objectType.expectKind {nnkObjectTy, nnkRefTy}
+
+  if objectType.kind == nnkRefTy:
+    objectType = objectType[0]
+
+  objectType.expectKind nnkObjectTy
+
+  var baseType = objectType[1]
+  if baseType.kind != nnkEmpty:
+    baseType.expectKind nnkOfInherit
+    baseType = baseType[0]
+    baseType.expectKind nnkSym
+    baseType = getImpl(baseType)
+    baseType.expectKind nnkTypeDef
+    baseType = baseType[2]
+    baseType.expectKind {nnkObjectTy, nnkRefTy}
+    collectFieldsInHierarchy result, baseType
+
+  let recList = objectType[2]
+  collectFieldsFromRecList result, recList
+
+proc recordFields*(typeImpl: NimNode): seq[FieldDescription] =
+  if typeImpl.isTuple:
+    for i in 1 ..< typeImpl.len:
+      result.add FieldDescription(typ: typeImpl[i], name: ident("Field" & $(i - 1)))
+    return
+
+  let objectType = case typeImpl.kind
+    of nnkObjectTy: typeImpl
+    of nnkTypeDef: typeImpl[2]
+    else:
+      macros.error("object type expected", typeImpl)
+      return
+
+  collectFieldsInHierarchy(result, objectType)
+
+macro field*(obj: typed, fieldName: static string): untyped =
+  newDotExpr(obj, ident fieldName)
+
+proc skipPragma*(n: NimNode): NimNode =
+  if n.kind == nnkPragmaExpr: n[0]
+  else: n
+
+
+{.pop.}