Generates predicates to test in diff functions in ComputedStyle

third_party/WebKit/Source/core/css/ComputedStyleDiffFunctions.json5

 {
   // This file specifies the fields we want to diff in the various diff functions 
   // in ComputedStyle.
 
   parameters: {
     // The name parameter represents the name of the function to be created.
 
     fields_to_diff: {
     },
 
     // A list of methods to diff (these can be public getters of fields or 
     // functions that use fields to determine a value).
     // Each entry is expressed as a dict of two fields.
     // The fields are method - the method to be diffed and field_dependencies
     // which lists the properties this method depends on.
     methods_to_diff: {
       default: [],
     },
+
+    // A list of predicates that have the diff logic built into them and are only
+    // called by the diff functions in ComputedStyle.
+    // Each entry is expressed as a dict of two fields.
+    // The fields are predicate - the predicate to be tested and field_dependencies
+    // which lists the properties this predicate test depends on.

[alancutter (OOO until 2018), 2017/05/24 07:29:36]

List the config fields with bullet points or a skeleton example to make it
easier to find quickly.
Mention the availability of the "other" variable.

[nainar, 2017/05/24 08:01:45]

Done.

+    predicates_to_test: {
+      default: [],
+    },
   },
   data: [
     {
         name: "ScrollAnchorDisablingPropertyChanged",
         fields_to_diff: ["width", "min-width", "max-width", "height", "min-height", "max-height", "margin-top", "margin-left", "margin-right", "margin-bottom", 
                   "left", "right", "top", "bottom", "padding-top", 
                   "padding-left", "padding-right", "padding-bottom"]
     },
     {
         name: "DiffNeedsFullLayoutAndPaintInvalidation",
         fields_to_diff: ["padding-top", "padding-left", "padding-right", 
                 "padding-bottom", "line-height", "font", "-webkit-border-horizontal-spacing", "-webkit-border-vertical-spacing"],
         methods_to_diff: [
           {
             method: "BorderLeftWidth()", 
             field_dependencies: ["border-left-width"]
           },
           {
             method: "BorderTopWidth()",
             field_dependencies: ["border-top-width"]
           },
           {
             method: "BorderBottomWidth()",
             field_dependencies: ["border-bottom-width"]
           },
           {
             method: "BorderRightWidth()",
             field_dependencies: ["border-right-width"]
           }
+        ],
+        predicates_to_test: [
+          {
+            predicate: "TextShadowDataEquivalent(other)",

[nainar, 2017/05/22 03:45:29]

could add the other as an argument bit in field.tmpl but then will have to pass
this in without brackets. so :/

[shend, 2017/05/22 03:51:05]

I would prefer not writing "other" in here, but it may not be possible if
predicates can take arguments.

[nainar1, 2017/05/22 03:52:55]

Yeah - I think leaving it here for the MVP and then seeing what way to go once
we have moved everything over is the best call to make at this stage.  

+            field_dependencies: ["text-shadow"]
+          },
+          {
+            predicate: "QuotesDataEquivalent(other)",
+            field_dependencies: ["quotes"]
+          },
         ]
     },
     {
         name: "DiffNeedsFullLayout",
         fields_to_diff: ["width", "min-width", "max-width", "height", "min-height", "max-height", "box-sizing"]
     }
   ],
 }