config: validate resource variables in output

config/config.go

@@ -106,7 +106,8 @@ func (c *Config) Validate() error {
 
 	// Check for references to user variables that do not actually
 	// exist and record those errors.
-	for source, v := range vars {
+	for source, vs := range vars {
+		for _, v := range vs {
 			uv, ok := v.(*UserVariable)
 			if !ok {
 				continue
@@ -119,13 +120,15 @@ func (c *Config) Validate() error {
 					uv.Name))
 			}
 		}
+	}
 
 	// Check that all references to resources are valid
 	resources := make(map[string]struct{})
 	for _, r := range c.Resources {
 		resources[r.Id()] = struct{}{}
 	}
-	for source, v := range vars {
+	for source, vs := range vars {
+		for _, v := range vs {
 			rv, ok := v.(*ResourceVariable)
 			if !ok {
 				continue
@@ -140,6 +143,9 @@ func (c *Config) Validate() error {
 					rv.FullKey()))
 			}
 		}
+	}
+
+	// Check that all outputs are valid
 
 	if len(errs) > 0 {
 		return &multierror.Error{Errors: errs}
@@ -151,19 +157,26 @@ func (c *Config) Validate() error {
 // allVariables is a helper that returns a mapping of all the interpolated
 // variables within the configuration. This is used to verify references
 // are valid in the Validate step.
-func (c *Config) allVariables() map[string]InterpolatedVariable {
-	result := make(map[string]InterpolatedVariable)
+func (c *Config) allVariables() map[string][]InterpolatedVariable {
+	result := make(map[string][]InterpolatedVariable)
 	for n, pc := range c.ProviderConfigs {
 		source := fmt.Sprintf("provider config '%s'", n)
 		for _, v := range pc.RawConfig.Variables {
-			result[source] = v
+			result[source] = append(result[source], v)
 		}
 	}
 
 	for _, rc := range c.Resources {
 		source := fmt.Sprintf("resource '%s'", rc.Id())
 		for _, v := range rc.RawConfig.Variables {
-			result[source] = v
+			result[source] = append(result[source], v)
+		}
+	}
+
+	for _, o := range c.Outputs {
+		source := fmt.Sprintf("output '%s'", o.Name)
+		for _, v := range o.RawConfig.Variables {
+			result[source] = append(result[source], v)
 		}
 	}
 

config/config_test.go

@@ -22,6 +22,13 @@ func TestConfigValidate_unknownResourceVar(t *testing.T) {
 	}
 }
 
+func TestConfigValidate_unknownResourceVar_output(t *testing.T) {
+	c := testConfig(t, "validate-unknown-resource-var-output")
+	if err := c.Validate(); err == nil {
+		t.Fatal("should not be valid")
+	}
+}
+
 func TestConfigValidate_unknownVar(t *testing.T) {
 	c := testConfig(t, "validate-unknownvar")
 	if err := c.Validate(); err == nil {

config/test-fixtures/validate-unknown-resource-var-output/main.tf

@@ -0,0 +1,6 @@
+resource "aws_instance" "web" {
+}
+
+output "ip" {
+  value = "${aws_instance.loadbalancer.foo}"
+}