Add pick and omit funcs

examples/vars.hcl

@@ -14,4 +14,15 @@ variable "bar" {
   value = {
     "this" = "that"
   }
+}
+
+variable "nested" {
+  value = [
+    {
+      "id" = "1"
+    },
+    {
+      "id" = "2"
+    }
+  ]
 }

interpolation/maps.go

@@ -108,3 +108,47 @@ func interpolationFuncMerge() ast.Function {
 		},
 	}
 }
+
+// interpolationFuncPick will pick the values of the provided keys, and create a new map
+func interpolationFuncPick() ast.Function {
+	return ast.Function{
+		ArgTypes:     []ast.Type{ast.TypeMap},
+		ReturnType:   ast.TypeMap,
+		Variadic:     true,
+		VariadicType: ast.TypeString,
+		Callback: func(inputs []interface{}) (interface{}, error) {
+			inMap := inputs[0].(map[string]ast.Variable)
+			result := make(map[string]ast.Variable)
+
+			for i := 1; i < len(inputs); i++ {
+				key := inputs[i].(string)
+
+				if val, ok := inMap[key]; ok {
+					result[key] = val
+				}
+			}
+
+			return result, nil
+		},
+	}
+}
+
+// interpolationFuncOmit will return a map that has omitted the keys provided
+func interpolationFuncOmit() ast.Function {
+	return ast.Function{
+		ArgTypes:     []ast.Type{ast.TypeMap},
+		ReturnType:   ast.TypeMap,
+		Variadic:     true,
+		VariadicType: ast.TypeString,
+		Callback: func(inputs []interface{}) (interface{}, error) {
+			inMap := inputs[0].(map[string]ast.Variable)
+
+			for i := 1; i < len(inputs); i++ {
+				key := inputs[i].(string)
+				delete(inMap, key)
+			}
+
+			return inMap, nil
+		},
+	}
+}

interpolation/maps_test.go

@@ -141,3 +141,49 @@ func TestInterpolationFuncMerge(t *testing.T) {
 		})
 	}
 }
+
+func TestInterpolationFuncPick(t *testing.T) {
+	testCases := []functionTestCase{
+		{
+			description: "Picks correctly",
+			text:        `${pick(map("foo", "bar", "this", "that"), "foo")}`,
+			expectation: map[string]interface{}{
+				"foo": "bar",
+			},
+		},
+	}
+
+	pickTestFunc := testInterpolationFunc(keyFuncs{
+		"pick": interpolationFuncPick,
+		"map":  interpolationFuncMap,
+	})
+
+	for _, tc := range testCases {
+		t.Run(tc.description, func(t *testing.T) {
+			pickTestFunc(t, tc)
+		})
+	}
+}
+
+func TestInterpolationFuncOmit(t *testing.T) {
+	testCases := []functionTestCase{
+		{
+			description: "Omit correctly",
+			text:        `${omit(map("foo", "bar", "this", "that"), "foo")}`,
+			expectation: map[string]interface{}{
+				"this": "that",
+			},
+		},
+	}
+
+	pickTestFunc := testInterpolationFunc(keyFuncs{
+		"omit": interpolationFuncOmit,
+		"map":  interpolationFuncMap,
+	})
+
+	for _, tc := range testCases {
+		t.Run(tc.description, func(t *testing.T) {
+			pickTestFunc(t, tc)
+		})
+	}
+}