Flow 0.69

[jfirebaugh]

Upgrade flow to 0.69. Not upgrading past that due to facebook/flow#6151.

One of the nice features in 0.68 is:

Previously, Flow would allow you to write if (foo.unknownProp) { ... }.
Now Flow disallows testing unknown properties in conditionals. If foo is a union type like { x: string } | { y: number }, x and y are known properties and z would be an unknown property

I remember finding a few bugs that would have been caught by this.

[asheemmamoowala]

Should there be a check for feature when using featureState? Feature state is only valid if there is a current feature. As it stands, it's possible to call Expression#evaluate with a null feature, but non-null featureState.

[jfirebaugh]

I'd like to fix it this way:

diff --git a/src/style-spec/expression/index.js b/src/style-spec/expression/index.js
index 1310db3f2..269f718ec 100644
--- a/src/style-spec/expression/index.js
+++ b/src/style-spec/expression/index.js
@@ -179,18 +179,18 @@ export class ZoomDependentExpression<Kind> {
 
 export type ConstantExpression = {
     kind: 'constant',
-    +evaluate: (globals: GlobalProperties, feature?: Feature) => any,
+    +evaluate: (globals: GlobalProperties) => any,
 }
 
 export type SourceExpression = {
     kind: 'source',
     isStateDependent: boolean,
-    +evaluate: (globals: GlobalProperties, feature?: Feature, featureState?: FeatureState) => any,
+    +evaluate: (globals: GlobalProperties, feature: Feature, featureState?: FeatureState) => any,
 };
 
 export type CameraExpression = {
     kind: 'camera',
-    +evaluate: (globals: GlobalProperties, feature?: Feature, featureState?: FeatureState) => any,
+    +evaluate: (globals: GlobalProperties, feature: Feature, featureState?: FeatureState) => any,
     +interpolationFactor: (input: number, lower: number, upper: number) => number,
     zoomStops: Array<number>
 };
@@ -198,7 +198,7 @@ export type CameraExpression = {
 export type CompositeExpression = {
     kind: 'composite',
     isStateDependent: boolean,
-    +evaluate: (globals: GlobalProperties, feature?: Feature, featureState?: FeatureState) => any,
+    +evaluate: (globals: GlobalProperties, feature: Feature, featureState?: FeatureState) => any,
     +interpolationFactor: (input: number, lower: number, upper: number) => number,
     zoomStops: Array<number>
 };

But this requires #6255 (comment), so I'd like to defer it.

However, in looking at this, I noticed that I'd failed to update ZoomDependentExpression#evaluate[WithoutErrorHandling] -- I've added additional render tests to cover that case.

[asheemmamoowala]

This seems reasonable. #6255 is needed soon, and I don't see an actual code path at this time where this issue would come up.