internal/pkg: make CallCtxt.Decimal support *adt.Vertex

The cue.Value.Decimal method currently makes the assumption that
its function argument is an *adt.Num. This means that the "Validator"
form of the builtin math.MultipleOf(n) will not work, because in that
case the first argument will be an *adt.Vertex.

This changes the explicit interface convertion to instead use the
cue.value.Decimal method, which will work in all cases.

Fixes #2927

Signed-off-by: Noam Dolovich <noam.tzvi.dolovich@gmail.com>
Change-Id: I35f780efde92a6523548ed04e1e7a6a960b191ce
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1184631
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>

internal/pkg/context.go

@@ -18,11 +18,12 @@ import (
 	"io"
 	"math/big"
 
+	"github.com/cockroachdb/apd/v3"
+
 	"cuelang.org/go/cue"
 	"cuelang.org/go/cue/token"
 	"cuelang.org/go/internal/core/adt"
 	"cuelang.org/go/internal/value"
-	"github.com/cockroachdb/apd/v3"
 )
 
 // CallCtxt is passed to builtin implementations that need to use a cue.Value. This is an internal type. Its interface may change.
@@ -129,11 +130,12 @@ func (c *CallCtxt) uintValue(i, bits int, typ string) uint64 {
 
 func (c *CallCtxt) Decimal(i int) *apd.Decimal {
 	x := value.Make(c.ctx, c.args[i])
-	if _, err := x.MantExp(nil); err != nil {
+	res, err := x.Decimal()
+	if err != nil {
 		c.invalidArgType(c.args[i], i, "Decimal", err)
 		return nil
 	}
-	return &c.args[i].(*adt.Num).X
+	return res
 }
 
 func (c *CallCtxt) Float64(i int) float64 {

pkg/math/testdata/round.txtar

@@ -11,6 +11,9 @@ mul3: math.MultipleOf(100, 1.00001)
 mul4: math.MultipleOf(1, 1)
 mul5: math.MultipleOf(5, 2.5)
 mul6: math.MultipleOf(100e100, 10)
+mul7: 10
+mul7: math.MultipleOf(2)
+mul8: 9 & math.MultipleOf(3)
 
 r0: math.Round(2.5)
 r1: math.Round(-2.5)
@@ -36,9 +39,9 @@ Errors:
 mul2: error in call to math.MultipleOf: division by zero:
     ./in.cue:6:7
 floorE1: too many arguments in call to math.Floor (have 2, want 1):
-    ./in.cue:17:10
+    ./in.cue:20:10
 floorE2: cannot use "foo" (type string) as number in argument 1 to math.Floor:
-    ./in.cue:18:21
+    ./in.cue:21:21
 
 Result:
 mul0: true
@@ -49,6 +52,8 @@ mul3:    false
 mul4:    true
 mul5:    true
 mul6:    true
+mul7:    10
+mul8:    9
 r0:      3
 r1:      -3
 r2:      2