config: new "abs" interpolation function

This new function returns the absolute value for a given number.

config/interpolate_funcs.go

@@ -58,6 +58,7 @@ func listVariableValueToStringSlice(values []ast.Variable) ([]string, error) {
 // Funcs is the mapping of built-in functions for configuration.
 func Funcs() map[string]ast.Function {
 	return map[string]ast.Function{
+		"abs":          interpolationFuncAbs(),
 		"basename":     interpolationFuncBasename(),
 		"base64decode": interpolationFuncBase64Decode(),
 		"base64encode": interpolationFuncBase64Encode(),
@@ -1546,3 +1547,14 @@ func interpolationFuncURLEncode() ast.Function {
 		},
 	}
 }
+
+// interpolationFuncAbs returns the absolute value of a given float.
+func interpolationFuncAbs() ast.Function {
+	return ast.Function{
+		ArgTypes:   []ast.Type{ast.TypeFloat},
+		ReturnType: ast.TypeFloat,
+		Callback: func(args []interface{}) (interface{}, error) {
+			return math.Abs(args[0].(float64)), nil
+		},
+	}
+}

config/interpolate_funcs_test.go

@@ -2612,3 +2612,55 @@ func TestInterpolateFuncURLEncode(t *testing.T) {
 		},
 	})
 }
+
+func TestInterpolateFuncAbs(t *testing.T) {
+	testFunction(t, testFunctionConfig{
+		Cases: []testFunctionCase{
+			{
+				`${abs()}`,
+				nil,
+				true,
+			},
+			{
+				`${abs("")}`,
+				nil,
+				true,
+			},
+			{
+				`${abs(0)}`,
+				"0",
+				false,
+			},
+			{
+				`${abs(1)}`,
+				"1",
+				false,
+			},
+			{
+				`${abs(-1)}`,
+				"1",
+				false,
+			},
+			{
+				`${abs(1.0)}`,
+				"1",
+				false,
+			},
+			{
+				`${abs(-1.0)}`,
+				"1",
+				false,
+			},
+			{
+				`${abs(-3.14)}`,
+				"3.14",
+				false,
+			},
+			{
+				`${abs(-42.001)}`,
+				"42.001",
+				false,
+			},
+		},
+	})
+}

website/docs/configuration/interpolation.html.md

@@ -145,6 +145,10 @@ syntax `name(arg, arg2, ...)`. For example, to read a file:
 
 The supported built-in functions are:
 
+  * `abs(float)` - Returns the absolute value of a given float.
+    Example: `abs(1)` returns `1`, and `abs(-1)` would also return `1`,
+    whereas `abs(-3.14)` would return `3.14`. See also the `signum` function.
+
   * `basename(path)` - Returns the last element of a path.
 
   * `base64decode(string)` - Given a base64-encoded string, decodes it and
@@ -358,7 +362,7 @@ The supported built-in functions are:
     SHA-512 hash of the given string.
     Example: `"${sha512("${aws_vpc.default.tags.customer}-s3-bucket")}"`
 
-  * `signum(int)` - Returns `-1` for negative numbers, `0` for `0` and `1` for positive numbers.
+  * `signum(integer)` - Returns `-1` for negative numbers, `0` for `0` and `1` for positive numbers.
       This function is useful when you need to set a value for the first resource and
       a different value for the rest of the resources.
       Example: `element(split(",", var.r53_failover_policy), signum(count.index))`