Expand the numeric conversions to template funcs/methods

So the example mentioned in #14079 also works for TOML and JSON front matter.

See #14079

common/hreflect/helpers.go

@@ -315,6 +315,7 @@ func IsContextType(tp reflect.Type) bool {
 // This is currently only implemented for int kinds,
 // added to handle the move to a new YAML library which produces uint64 for unsigned integers.
 // We can expand on this later if needed.
+// This conversion is lossless.
 // See Issue 14079.
 func ConvertIfPossible(val reflect.Value, typ reflect.Type) (reflect.Value, bool) {
 	if IsInt(typ.Kind()) {
@@ -333,6 +334,21 @@ func ConvertIfPossible(val reflect.Value, typ reflect.Type) (reflect.Value, bool
 			}
 			return val.Convert(typ), true
 		}
+		if IsFloat(val.Kind()) {
+			f := val.Float()
+			if f < float64(math.MinInt64) || f > float64(math.MaxInt64) {
+				return reflect.Value{}, false
+			}
+			i := int64(f)
+			if typ.OverflowInt(i) {
+				return reflect.Value{}, false
+			}
+			// Check for lossless conversion.
+			if float64(i) != f {
+				return reflect.Value{}, false
+			}
+			return val.Convert(typ), true
+		}
 	}
 	return reflect.Value{}, false
 }

common/hreflect/helpers_test.go

@@ -231,6 +231,33 @@ func TestCastIfPossible(t *testing.T) {
 			ok:       true,
 			expected: int(math.MaxInt16),
 		},
+		// From float to int.
+		{
+			name:  "float64(1.5) to int",
+			value: float64(1.5),
+			typ:   int(0),
+			ok:    false, // loss of precision
+		},
+		{
+			name:     "float64(1.0) to int",
+			value:    float64(1.0),
+			typ:      int(0),
+			ok:       true,
+			expected: int(1),
+		},
+		{
+			name:  "float64(math.MaxFloat64) to int16",
+			value: float64(math.MaxFloat64),
+			typ:   int16(0),
+			ok:    false, // overflow
+		},
+		{
+			name:     "float64(32767) to int16",
+			value:    float64(32767),
+			typ:      int16(0),
+			ok:       true,
+			expected: int16(32767),
+		},
 	} {
 
 		v, ok := ConvertIfPossible(reflect.ValueOf(test.value), reflect.TypeOf(test.typ))