config: accept file("test.txt") [GH-145]

config/interpolate_walk.go

@@ -11,7 +11,7 @@ import (
 
 // interpRegexp is a regexp that matches interpolations such as ${foo.bar}
 var interpRegexp *regexp.Regexp = regexp.MustCompile(
-	`(?i)(\$+)\{([\s*-.,\(\)a-z0-9_]+)\}`)
+	`(?i)(\$+)\{([\s*-.,\(\)a-z0-9_"]+)\}`)
 
 // interpolationWalker implements interfaces for the reflectwalk package
 // (github.com/mitchellh/reflectwalk) that can be used to automatically

config/interpolate_walk_test.go

@@ -71,6 +71,22 @@ func TestInterpolationWalker_detect(t *testing.T) {
 				},
 			},
 		},
+
+		{
+			Input: map[string]interface{}{
+				"foo": `${file("test.txt")}`,
+			},
+			Result: []Interpolation{
+				&FunctionInterpolation{
+					Func: nil,
+					Args: []Interpolation{
+						&LiteralInterpolation{
+							Literal: "test.txt",
+						},
+					},
+				},
+			},
+		},
 	}
 
 	for i, tc := range cases {