fix: default untyped to uint when necessary (#2024)

Closes #2004. This change allows for passing a value to `defaultTypeOf`.
In the case where we are looking for the default value of an untyped
int, it can use the value, if it exists, in order to determine whether
the default type should be a signed or unsigned int.
<!-- please provide a detailed description of the changes made in this
pull request. -->

<details><summary>Contributors' checklist...</summary>

- [x] Added new tests, or not needed, or not feasible
- [x] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [x] Updated the official documentation or not needed
- [x] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [x] Added references to related issues and PRs
- [x] Provided any useful hints for running manual tests
- [x] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

---------

Co-authored-by: Miloš Živković <milos.zivkovic@tendermint.com>

gnovm/pkg/gnolang/preprocess.go

@@ -2477,7 +2477,7 @@ func checkOrConvertType(store Store, last BlockNode, x *Expr, t Type, autoNative
 		// convert type
 		if isUntyped(xt) { // convert if x is untyped literal
 			if t == nil {
-				t = defaultTypeOf(xt)
+				t = defaultTypeOf(xt, nil)
 			}
 			// Push type into expr if qualifying binary expr.
 			if bx, ok := (*x).(*BinaryExpr); ok {

gnovm/pkg/gnolang/types.go

@@ -1203,8 +1203,8 @@ func (ft *FuncType) Specify(store Store, argTVs []TypedValue, isVarg bool) *Func
 					continue
 				} else if vargt == nil {
 					vargt = varg.T
-				} else if isUntyped(varg.T) && vargt.TypeID() == defaultTypeOf(varg.T).TypeID() {
-					vargt = defaultTypeOf(varg.T)
+				} else if isUntyped(varg.T) && vargt.TypeID() == defaultTypeOf(varg.T, varg.V).TypeID() {
+					vargt = defaultTypeOf(varg.T, varg.V)
 				} else if vargt.TypeID() != varg.T.TypeID() {
 					panic(fmt.Sprintf(
 						"incompatible varg types: expected %v, got %s",
@@ -2281,14 +2281,23 @@ func isDataByte(t Type) bool {
 
 // TODO move untyped const stuff to preprocess.go.
 // TODO associate with ConvertTo() in documentation.
-func defaultTypeOf(t Type) Type {
+func defaultTypeOf(t Type, v Value) Type {
 	switch t {
 	case UntypedBoolType:
 		return BoolType
 	case UntypedRuneType:
 		return Int32Type
 	case UntypedBigintType:
-		return IntType
+		typeVal := IntType
+		if bigintValue, ok := v.(BigintValue); ok {
+			if bigintValue.V != nil && bigintValue.V.Sign() == 1 && !bigintValue.V.IsInt64() {
+				// Use an unsigned type if the value is positive and we know
+				// it won't fit in an int64.
+				typeVal = Uint64Type
+			}
+		}
+
+		return typeVal
 	case UntypedBigdecType:
 		return Float64Type
 	case UntypedStringType:
@@ -2514,7 +2523,7 @@ func specifyType(store Store, lookup map[Name]Type, tmpl Type, spec Type, specTy
 					return // ok
 				} else {
 					if isUntyped(spec) {
-						spec = defaultTypeOf(spec)
+						spec = defaultTypeOf(spec, nil)
 					}
 					lookup[ct.Generic] = spec
 					return // ok

gnovm/pkg/gnolang/values.go

@@ -1594,7 +1594,7 @@ func (tv *TypedValue) Assign(alloc *Allocator, tv2 TypedValue, cu bool) {
 	}
 	*tv = tv2.Copy(alloc)
 	if cu && isUntyped(tv.T) {
-		ConvertUntypedTo(tv, defaultTypeOf(tv.T))
+		ConvertUntypedTo(tv, defaultTypeOf(tv.T, tv.V))
 	}
 }
 

gnovm/pkg/gnolang/values_conversions.go

@@ -926,7 +926,7 @@ func ConvertUntypedTo(tv *TypedValue, t Type) {
 	}
 	// general case
 	if t == nil {
-		t = defaultTypeOf(tv.T)
+		t = defaultTypeOf(tv.T, tv.V)
 	}
 	switch tv.T {
 	case UntypedBoolType:

gnovm/tests/files/bigint1.gno

@@ -0,0 +1,14 @@
+package main
+
+import (
+	"math"
+)
+
+func main() {
+	println(float64(math.MaxUint32))
+	println(float64(math.MaxUint64))
+}
+
+// Output:
+// 4.294967295e+09
+// 1.8446744073709552e+19