terraform: splatting with computed values is computed [GH-2744]

terraform/interpolate.go

@@ -433,6 +433,11 @@ func (i *Interpolater) computeResourceMultiVariable(
 			continue
 		}
 
+		// If any value is unknown, the whole thing is unknown
+		if attr == config.UnknownVariableValue {
+			return config.UnknownVariableValue, nil
+		}
+
 		values = append(values, attr)
 	}
 

terraform/interpolate_test.go

@@ -136,6 +136,80 @@ func TestInterpolater_pathRoot(t *testing.T) {
 	})
 }
 
+func TestInterpolater_resourceVariable(t *testing.T) {
+	lock := new(sync.RWMutex)
+	state := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: rootModulePath,
+				Resources: map[string]*ResourceState{
+					"aws_instance.web": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "bar",
+							Attributes: map[string]string{
+								"foo": "bar",
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+
+	i := &Interpolater{
+		Module:    testModule(t, "interpolate-resource-variable"),
+		State:     state,
+		StateLock: lock,
+	}
+
+	scope := &InterpolationScope{
+		Path: rootModulePath,
+	}
+
+	testInterpolate(t, i, scope, "aws_instance.web.foo", ast.Variable{
+		Value: "bar",
+		Type:  ast.TypeString,
+	})
+}
+
+func TestInterpolater_resourceVariableMulti(t *testing.T) {
+	lock := new(sync.RWMutex)
+	state := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: rootModulePath,
+				Resources: map[string]*ResourceState{
+					"aws_instance.web": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "bar",
+							Attributes: map[string]string{
+								"foo": config.UnknownVariableValue,
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+
+	i := &Interpolater{
+		Module:    testModule(t, "interpolate-resource-variable"),
+		State:     state,
+		StateLock: lock,
+	}
+
+	scope := &InterpolationScope{
+		Path: rootModulePath,
+	}
+
+	testInterpolate(t, i, scope, "aws_instance.web.*.foo", ast.Variable{
+		Value: config.UnknownVariableValue,
+		Type:  ast.TypeString,
+	})
+}
+
 func testInterpolate(
 	t *testing.T, i *Interpolater,
 	scope *InterpolationScope,

terraform/test-fixtures/interpolate-resource-variable/main.tf

@@ -0,0 +1 @@
+resource "aws_instance" "web" {}