release-20.2: opt: fix FoldJSONAccessIntoValues corner case

pkg/sql/opt/norm/project_funcs.go

@@ -368,6 +368,11 @@ func (c *CustomFuncs) CanUnnestJSONFromValues(
 			return false
 		}
 		currJSON := expr.(*memo.ConstExpr).Value.(*tree.DJSON)
+		if currJSON.Type() != json.ObjectJSONType {
+			// This value is not an object. It is important to check, because a JSON
+			// array can pass the checks below (see #60522).
+			return false
+		}
 		iter, err := firstJSON.ObjectIter()
 		if err != nil {
 			return false

pkg/sql/opt/norm/testdata/rules/project

@@ -1478,3 +1478,20 @@ project
  │    └── ('{"y": "three"}',)
  └── projections
       └── column1:1::JSONB->'x' [as=x:2, outer=(1), immutable]
+
+# Verify that the rule doesn't fire because of an array that has the right key
+# as an element (#60522).
+norm expect-not=FoldJSONAccessIntoValues
+SELECT j->'foo' FROM (VALUES ('{"foo": "bar"}'::JSONB), ('["foo", "baz"]'::JSONB)) AS v(j)
+----
+project
+ ├── columns: "?column?":2
+ ├── cardinality: [2 - 2]
+ ├── immutable
+ ├── values
+ │    ├── columns: column1:1!null
+ │    ├── cardinality: [2 - 2]
+ │    ├── ('{"foo": "bar"}',)
+ │    └── ('["foo", "baz"]',)
+ └── projections
+      └── column1:1->'foo' [as="?column?":2, outer=(1), immutable]

pkg/util/json/json.go

@@ -117,7 +117,11 @@ type JSON interface {
 	// AsText returns the JSON document as a string, with quotes around strings removed, and null as nil.
 	AsText() (*string, error)
 
-	// Exists implements the `?` operator.
+	// Exists implements the `?` operator: does the string exist as a top-level
+	// key within the JSON value?
+	//
+	// If the object is a JSON array, returns true when the key is a top-level
+	// element of the array.
 	Exists(string) (bool, error)
 
 	// StripNulls returns the JSON document with all object fields that have null values omitted