remove fauxMatch for tyFromExpr, remove tyProxy and tyUnknown aliases (#24018)

updated version of #22193

After #22029 and the followups #23983 and #24005 which fixed issues with
it, `tyFromExpr` no longer match any proc params in generic type bodies
but delay all non-matching calls until the type is instantiated.
Previously the mechanism `fauxMatch` was used to pretend that any
failing match against `tyFromExpr` actually matched, but prevented the
instantiation of the type until later.

Since this mechanism is not needed anymore for `tyFromExpr`, it is now
only used for `tyError` to prevent cascading errors and changed to a
bool field for simplicity. A change in `semtypes` was also needed to
prevent calling `fitNode` on default param values resolving to type
`tyFromExpr` in generic procs for params with non-generic types, as this
would try to coerce the expression into a concrete type when it can't be
instantiated yet.

The aliases `tyProxy` and `tyUnknown` for `tyError` and `tyFromExpr` are
also removed for uniformity.

15 files changed, 31 insertions, 39 deletions

diff --git a/compiler/ast.nim b/compiler/ast.nim
index d0d4f8db3..db6cd9761 100644
--- a/compiler/ast.nim
+++ b/compiler/ast.nim
@@ -214,7 +214,8 @@ type
     tyUncheckedArray
       # An array with boundaries [0,+∞]
 
-    tyProxy # used as errornous type (for idetools)
+    tyError # used as erroneous type (for idetools)
+      # as an erroneous node should match everything
 
     tyBuiltInTypeClass
       # Type such as the catch-all object, tuple, seq, etc
@@ -276,10 +277,6 @@ static:
 const
   tyPureObject* = tyTuple
   GcTypeKinds* = {tyRef, tySequence, tyString}
-  tyError* = tyProxy # as an errornous node should match everything
-  tyUnknown* = tyFromExpr
-
-  tyUnknownTypes* = {tyError, tyFromExpr}
 
   tyTypeClasses* = {tyBuiltInTypeClass, tyCompositeTypeClass,
                     tyUserTypeClass, tyUserTypeClassInst,
diff --git a/compiler/ccgreset.nim b/compiler/ccgreset.nim
index 29791afdc..6caeb8084 100644
--- a/compiler/ccgreset.nim
+++ b/compiler/ccgreset.nim
@@ -96,7 +96,7 @@ proc specializeResetT(p: BProc, accessor: Rope, typ: PType) =
       raiseAssert "unexpected set type kind"
   of tyNone, tyEmpty, tyNil, tyUntyped, tyTyped, tyGenericInvocation,
       tyGenericParam, tyOrdinal, tyOpenArray, tyForward, tyVarargs,
-      tyUncheckedArray, tyProxy, tyBuiltInTypeClass, tyUserTypeClass,
+      tyUncheckedArray, tyError, tyBuiltInTypeClass, tyUserTypeClass,
       tyUserTypeClassInst, tyCompositeTypeClass, tyAnd, tyOr, tyNot,
       tyAnything, tyStatic, tyFromExpr, tyConcept, tyVoid, tyIterable:
     discard
diff --git a/compiler/expanddefaults.nim b/compiler/expanddefaults.nim
index c121f5dea..c520d8849 100644
--- a/compiler/expanddefaults.nim
+++ b/compiler/expanddefaults.nim
@@ -125,7 +125,7 @@ proc expandDefault(t: PType; info: TLineInfo): PNode =
   of tyString:
     result = newZero(t, info, nkStrLit)
   of tyNone, tyEmpty, tyUntyped, tyTyped, tyTypeDesc,
-     tyNil, tyGenericInvocation, tyProxy, tyBuiltInTypeClass,
+     tyNil, tyGenericInvocation, tyError, tyBuiltInTypeClass,
      tyUserTypeClass, tyUserTypeClassInst, tyCompositeTypeClass,
      tyAnd, tyOr, tyNot, tyAnything, tyConcept, tyIterable, tyForward:
     result = newZero(t, info, nkEmpty) # bug indicator
diff --git a/compiler/jsgen.nim b/compiler/jsgen.nim
index 657994b0d..d6310d584 100644
--- a/compiler/jsgen.nim
+++ b/compiler/jsgen.nim
@@ -195,7 +195,7 @@ proc mapType(typ: PType): TJSTypeKind =
   of tyPointer:
     # treat a tyPointer like a typed pointer to an array of bytes
     result = etyBaseIndex
-  of tyRange, tyDistinct, tyOrdinal, tyProxy, tyLent:
+  of tyRange, tyDistinct, tyOrdinal, tyError, tyLent:
     # tyLent is no-op as JS has pass-by-reference semantics
     result = mapType(skipModifier t)
   of tyInt..tyInt64, tyUInt..tyUInt64, tyEnum, tyChar: result = etyInt
diff --git a/compiler/liftdestructors.nim b/compiler/liftdestructors.nim
index 0bbaf3b33..2cf8afb62 100644
--- a/compiler/liftdestructors.nim
+++ b/compiler/liftdestructors.nim
@@ -1040,7 +1040,7 @@ proc fillBody(c: var TLiftCtx; t: PType; body, x, y: PNode) =
     else:
       discard "cannot copy openArray"
 
-  of tyFromExpr, tyProxy, tyBuiltInTypeClass, tyUserTypeClass,
+  of tyFromExpr, tyError, tyBuiltInTypeClass, tyUserTypeClass,
      tyUserTypeClassInst, tyCompositeTypeClass, tyAnd, tyOr, tyNot, tyAnything,
      tyGenericParam, tyGenericBody, tyNil, tyUntyped, tyTyped,
      tyTypeDesc, tyGenericInvocation, tyForward, tyStatic:
diff --git a/compiler/semcall.nim b/compiler/semcall.nim
index 7040c1ac6..14e8591ba 100644
--- a/compiler/semcall.nim
+++ b/compiler/semcall.nim
@@ -696,12 +696,12 @@ proc semResolvedCall(c: PContext, x: var TCandidate,
   markUsed(c, info, finalCallee)
   onUse(info, finalCallee)
   assert finalCallee.ast != nil
-  if x.hasFauxMatch:
+  if x.matchedErrorType:
     result = x.call
     result[0] = newSymNode(finalCallee, getCallLineInfo(result[0]))
-    if containsGenericType(result.typ) or x.fauxMatch == tyUnknown:
-      result.typ = newTypeS(x.fauxMatch, c)
-      if result.typ.kind == tyError: incl result.typ.flags, tfCheckedForDestructor
+    if containsGenericType(result.typ):
+      result.typ = newTypeS(tyError, c)
+      incl result.typ.flags, tfCheckedForDestructor
     return
   let gp = finalCallee.ast[genericParamsPos]
   if gp.isGenericParams:
diff --git a/compiler/semstmts.nim b/compiler/semstmts.nim
index 185441815..be60b093d 100644
--- a/compiler/semstmts.nim
+++ b/compiler/semstmts.nim
@@ -2859,7 +2859,7 @@ proc semStmtList(c: PContext, n: PNode, flags: TExprFlags, expectedType: PType =
         let verdict = semConstExpr(c, n[i])
         if verdict == nil or verdict.kind != nkIntLit or verdict.intVal == 0:
           localError(c.config, result.info, "concept predicate failed")
-      of tyUnknown: continue
+      of tyFromExpr: continue
       else: discard
     if n[i].typ == c.enforceVoidContext: #or usesResult(n[i]):
       voidContext = true
diff --git a/compiler/semtypes.nim b/compiler/semtypes.nim
index 2a5b6c751..292558b5b 100644
--- a/compiler/semtypes.nim
+++ b/compiler/semtypes.nim
@@ -1385,7 +1385,7 @@ proc semProcTypeNode(c: PContext, n, genericParams: PNode,
           typ = newTypeS(tyTypeDesc, c, newTypeS(tyNone, c))
           typ.flags.incl tfCheckedForDestructor
 
-      else:
+      elif def.typ.kind != tyFromExpr:
         # if def.typ != nil and def.typ.kind != tyNone:
         # example code that triggers it:
         # proc sort[T](cmp: proc(a, b: T): int = cmp)
diff --git a/compiler/sigmatch.nim b/compiler/sigmatch.nim
index 1650e8598..89b66b524 100644
--- a/compiler/sigmatch.nim
+++ b/compiler/sigmatch.nim
@@ -59,8 +59,8 @@ type
     magic*: TMagic           # magic of operation
     baseTypeMatch: bool      # needed for conversions from T to openarray[T]
                              # for example
-    fauxMatch*: TTypeKind    # the match was successful only due to the use
-                             # of error or wildcard (unknown) types.
+    matchedErrorType*: bool  # match is considered successful after matching
+                             # error type to avoid cascading errors
                              # this is used to prevent instantiations.
     genericConverter*: bool  # true if a generic converter needs to
                              # be instantiated
@@ -101,8 +101,6 @@ const
 proc markUsed*(c: PContext; info: TLineInfo, s: PSym; checkStyle = true)
 proc markOwnerModuleAsUsed*(c: PContext; s: PSym)
 
-template hasFauxMatch*(c: TCandidate): bool = c.fauxMatch != tyNone
-
 proc initCandidateAux(ctx: PContext,
                       callee: PType): TCandidate {.inline.} =
   result = TCandidate(c: ctx, exactMatches: 0, subtypeMatches: 0,
@@ -813,7 +811,7 @@ proc matchUserTypeClass*(m: var TCandidate; ff, a: PType): PType =
             param.typ.flags.incl tfInferrableStatic
           else:
             param.ast = typ.n
-        of tyUnknown:
+        of tyFromExpr:
           param = paramSym skVar
           param.typ = typ.exactReplica
           #copyType(typ, c.idgen, typ.owner)
@@ -1971,7 +1969,7 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
     if aOrig != nil:
       put(c, f, aOrig)
     result = isGeneric
-  of tyProxy:
+  of tyError:
     result = isEqual
   of tyFromExpr:
     # fix the expression, so it contains the already instantiated types
@@ -2037,7 +2035,7 @@ proc implicitConv(kind: TNodeKind, f: PType, arg: PNode, m: TCandidate,
                   c: PContext): PNode =
   result = newNodeI(kind, arg.info)
   if containsGenericType(f):
-    if not m.hasFauxMatch:
+    if not m.matchedErrorType:
       result.typ = getInstantiatedType(c, arg, m, f).skipTypes({tySink})
     else:
       result.typ = errorType(c)
@@ -2329,13 +2327,10 @@ proc paramTypesMatchAux(m: var TCandidate, f, a: PType,
       result = implicitConv(nkHiddenSubConv, f, arg, m, c)
   of isNone:
     # do not do this in ``typeRel`` as it then can't infer T in ``ref T``:
-    if a.kind in {tyProxy, tyUnknown}:
-      if a.kind == tyUnknown and c.inGenericContext > 0:
-        # don't bother with fauxMatch mechanism in generic type,
-        # reject match, typechecking will be delayed to instantiation
-        return nil
+    if a.kind == tyFromExpr: return nil
+    elif a.kind == tyError:
       inc(m.genericMatches)
-      m.fauxMatch = a.kind
+      m.matchedErrorType = true
       return arg
     elif a.kind == tyVoid and f.matchesVoidProc and argOrig.kind == nkStmtList:
       # lift do blocks without params to lambdas
@@ -2505,7 +2500,7 @@ proc setSon(father: PNode, at: int, son: PNode) =
 # we are allowed to modify the calling node in the 'prepare*' procs:
 proc prepareOperand(c: PContext; formal: PType; a: PNode): PNode =
   if formal.kind == tyUntyped and formal.len != 1:
-    # {tyTypeDesc, tyUntyped, tyTyped, tyProxy}:
+    # {tyTypeDesc, tyUntyped, tyTyped, tyError}:
     # a.typ == nil is valid
     result = a
   elif a.typ.isNil:
diff --git a/compiler/typeallowed.nim b/compiler/typeallowed.nim
index 2f757bb62..39193a42d 100644
--- a/compiler/typeallowed.nim
+++ b/compiler/typeallowed.nim
@@ -200,7 +200,7 @@ proc typeAllowedAux(marker: var IntSet, typ: PType, kind: TSymKind,
       result = typeAllowedNode(marker, t.n, kind, c, flags)
   of tyEmpty:
     if kind in {skVar, skLet}: result = t
-  of tyProxy:
+  of tyError:
     # for now same as error node; we say it's a valid type as it should
     # prevent cascading errors:
     result = nil
diff --git a/compiler/types.nim b/compiler/types.nim
index 9dbbc3b8b..786fe0b0c 100644
--- a/compiler/types.nim
+++ b/compiler/types.nim
@@ -776,7 +776,7 @@ proc typeToString(typ: PType, prefer: TPreferedDesc = preferName): string =
 
 proc firstOrd*(conf: ConfigRef; t: PType): Int128 =
   case t.kind
-  of tyBool, tyChar, tySequence, tyOpenArray, tyString, tyVarargs, tyProxy:
+  of tyBool, tyChar, tySequence, tyOpenArray, tyString, tyVarargs, tyError:
     result = Zero
   of tySet, tyVar: result = firstOrd(conf, t.elementType)
   of tyArray: result = firstOrd(conf, t.indexType)
@@ -909,7 +909,7 @@ proc lastOrd*(conf: ConfigRef; t: PType): Int128 =
     result = lastOrd(conf, skipModifier(t))
   of tyUserTypeClasses:
     result = lastOrd(conf, last(t))
-  of tyProxy: result = Zero
+  of tyError: result = Zero
   of tyOrdinal:
     if t.hasElementType: result = lastOrd(conf, skipModifier(t))
     else:
diff --git a/compiler/vmdeps.nim b/compiler/vmdeps.nim
index e293ab7b2..5f9a2b5bc 100644
--- a/compiler/vmdeps.nim
+++ b/compiler/vmdeps.nim
@@ -282,7 +282,7 @@ proc mapTypeToAstX(cache: IdentCache; t: PType; info: TLineInfo;
   of tyUInt32: result = atomicType("uint32", mUInt32)
   of tyUInt64: result = atomicType("uint64", mUInt64)
   of tyVarargs: result = mapTypeToBracket("varargs", mVarargs, t, info)
-  of tyProxy: result = atomicType("error", mNone)
+  of tyError: result = atomicType("error", mNone)
   of tyBuiltInTypeClass:
     result = mapTypeToBracket("builtinTypeClass", mNone, t, info)
   of tyUserTypeClass, tyUserTypeClassInst:
diff --git a/lib/system/hti.nim b/lib/system/hti.nim
index 9acaae88b..a26aff982 100644
--- a/lib/system/hti.nim
+++ b/lib/system/hti.nim
@@ -59,7 +59,7 @@ type
     tyOwned, tyUnused1, tyUnused2,
     tyVarargsHidden,
     tyUncheckedArray,
-    tyProxyHidden,
+    tyErrorHidden,
     tyBuiltInTypeClassHidden,
     tyUserTypeClassHidden,
     tyUserTypeClassInstHidden,
diff --git a/tests/generics/tstatic_constrained.nim b/tests/generics/tstatic_constrained.nim
index 3c9201548..d356b9d1c 100644
--- a/tests/generics/tstatic_constrained.nim
+++ b/tests/generics/tstatic_constrained.nim
@@ -8,7 +8,7 @@ but expected: <T: float or string, Y>
 tstatic_constrained.nim(44, 22) Error: cannot instantiate MyOtherType [type declared in tstatic_constrained.nim(30, 5)]
 got: <typedesc[int], int literal(10)>
 but expected: <T: float or string, Y>
-tstatic_constrained.nim(44, 31) Error: object constructor needs an object type [proxy]
+tstatic_constrained.nim(44, 31) Error: object constructor needs an object type [error]
 tstatic_constrained.nim(44, 31) Error: expression '' has no type (or is ambiguous)
 tstatic_constrained.nim(45, 22) Error: cannot instantiate MyOtherType [type declared in tstatic_constrained.nim(30, 5)]
 got: <typedesc[byte], uint8>
@@ -16,7 +16,7 @@ but expected: <T: float or string, Y>
 tstatic_constrained.nim(45, 22) Error: cannot instantiate MyOtherType [type declared in tstatic_constrained.nim(30, 5)]
 got: <typedesc[byte], uint8>
 but expected: <T: float or string, Y>
-tstatic_constrained.nim(45, 34) Error: object constructor needs an object type [proxy]
+tstatic_constrained.nim(45, 34) Error: object constructor needs an object type [error]
 tstatic_constrained.nim(45, 34) Error: expression '' has no type (or is ambiguous)
 tstatic_constrained.nim(77, 14) Error: cannot instantiate MyType [type declared in tstatic_constrained.nim(71, 5)]
 got: <typedesc[float], float64>
@@ -76,4 +76,4 @@ block:
     b: MyType[string, "hello"]
     c: MyType[float, 10d]
     d: MyOtherType[MyOtherConstraint[float],MyOtherConstraint[float]()]
-    e: MyOtherType[MyOtherConstraint[int], MyOtherConstraint[int]()]
\ No newline at end of file
+    e: MyOtherType[MyOtherConstraint[int], MyOtherConstraint[int]()]
diff --git a/tests/types/tinheritgenericparameter.nim b/tests/types/tinheritgenericparameter.nim
index c88c50b7b..d0d313635 100644
--- a/tests/types/tinheritgenericparameter.nim
+++ b/tests/types/tinheritgenericparameter.nim
@@ -4,11 +4,11 @@ discard """
   nimout:'''
 tinheritgenericparameter.nim(36, 15) Error: Cannot inherit from: 'MyObject'
 tinheritgenericparameter.nim(36, 15) Error: Cannot inherit from: 'MyObject'
-tinheritgenericparameter.nim(36, 23) Error: object constructor needs an object type [proxy]
+tinheritgenericparameter.nim(36, 23) Error: object constructor needs an object type [error]
 tinheritgenericparameter.nim(36, 23) Error: expression '' has no type (or is ambiguous)
 tinheritgenericparameter.nim(37, 15) Error: Cannot inherit from: 'int'
 tinheritgenericparameter.nim(37, 15) Error: Cannot inherit from: 'int'
-tinheritgenericparameter.nim(37, 23) Error: object constructor needs an object type [proxy]
+tinheritgenericparameter.nim(37, 23) Error: object constructor needs an object type [error]
 tinheritgenericparameter.nim(37, 23) Error: expression '' has no type (or is ambiguous)
 '''
 """