tpl: Add math.Abs

Fixes #10941.

tpl/math/init.go

@@ -31,6 +31,13 @@ func init() {
 			Context: func(cctx context.Context, args ...any) (any, error) { return ctx, nil },
 		}
 
+		ns.AddMethodMapping(ctx.Abs,
+			nil,
+			[][2]string{
+				{"{{ math.Abs -2.1 }}", "2.1"},
+			},
+		)
+
 		ns.AddMethodMapping(ctx.Add,
 			[]string{"add"},
 			[][2]string{

tpl/math/math.go

@@ -35,6 +35,16 @@ func New() *Namespace {
 // Namespace provides template functions for the "math" namespace.
 type Namespace struct{}
 
+// Abs returns the absolute value of n.
+func (ns *Namespace) Abs(n any) (float64, error) {
+	af, err := cast.ToFloat64E(n)
+	if err != nil {
+		return 0, errors.New("the math.Abs function requires a numeric argument")
+	}
+
+	return math.Abs(af), nil
+}
+
 // Add adds the multivalued addends n1 and n2 or more values.
 func (ns *Namespace) Add(inputs ...any) (any, error) {
 	return ns.doArithmetic(inputs, '+')

tpl/math/math_test.go

@@ -63,6 +63,33 @@ func TestBasicNSArithmetic(t *testing.T) {
 	}
 }
 
+func TestAbs(t *testing.T) {
+	t.Parallel()
+	c := qt.New(t)
+	ns := New()
+
+	for _, test := range []struct {
+		x      any
+		expect any
+	}{
+		{0.0, 0.0},
+		{1.5, 1.5},
+		{-1.5, 1.5},
+		{-2, 2.0},
+		{"abc", false},
+	} {
+		result, err := ns.Abs(test.x)
+
+		if b, ok := test.expect.(bool); ok && !b {
+			c.Assert(err, qt.Not(qt.IsNil))
+			continue
+		}
+
+		c.Assert(err, qt.IsNil)
+		c.Assert(result, qt.Equals, test.expect)
+	}
+}
+
 func TestCeil(t *testing.T) {
 	t.Parallel()
 	c := qt.New(t)