Always shard structs if they would exceed maxNameSize even if unfiltered

Previously, a struct (anonymous or named) whose fields all matched the
predicate would not be sharded and would simply be reused. However,
that could break the maxNameSize limitation which could cause problems
for the caller.

This change makes sure that the supplied struct is only reused if it
does not exceed the maxNameSize, and otherwise is sharded.

Bug: 183777071
Test: m nothing
Change-Id: I8af272ec121077a43333e72b67cfd0e493c83362

proptools/filter.go

@@ -173,7 +173,13 @@ func filterPropertyStruct(prop reflect.Type, prefix string, maxNameSize int,
 		return nil, true
 	}
 
-	if !filtered {
+	// If the predicate selected all fields in the structure then it is generally better to reuse the
+	// original type as it avoids the footprint of creating another type. Also, if the original type
+	// is a named type then it will reduce the size of any structs the caller may create that include
+	// fields of this type. However, the original type should only be reused if it does not exceed
+	// maxNameSize. That is, of course, more likely for an anonymous type than a named one but this
+	// treats them the same.
+	if !filtered && (maxNameSize < 0 || len(prop.String()) < maxNameSize) {
 		if ptr {
 			return []reflect.Type{reflect.PtrTo(prop)}, false
 		}

proptools/filter_test.go

@@ -240,6 +240,12 @@ func TestFilterPropertyStruct(t *testing.T) {
 }
 
 func TestFilterPropertyStructSharded(t *testing.T) {
+	type KeepAllWithAReallyLongNameThatExceedsTheMaxNameSize struct {
+		A *string `keep:"true"`
+		B *string `keep:"true"`
+		C *string `keep:"true"`
+	}
+
 	tests := []struct {
 		name        string
 		maxNameSize int
@@ -266,6 +272,44 @@ func TestFilterPropertyStructSharded(t *testing.T) {
 			},
 			filtered: true,
 		},
+		{
+			name:        "anonymous where all match but still needs sharding",
+			maxNameSize: 20,
+			in: &struct {
+				A *string `keep:"true"`
+				B *string `keep:"true"`
+				C *string `keep:"true"`
+			}{},
+			out: []interface{}{
+				&struct {
+					A *string
+				}{},
+				&struct {
+					B *string
+				}{},
+				&struct {
+					C *string
+				}{},
+			},
+			filtered: true,
+		},
+		{
+			name:        "named where all match but still needs sharding",
+			maxNameSize: 20,
+			in:          &KeepAllWithAReallyLongNameThatExceedsTheMaxNameSize{},
+			out: []interface{}{
+				&struct {
+					A *string
+				}{},
+				&struct {
+					B *string
+				}{},
+				&struct {
+					C *string
+				}{},
+			},
+			filtered: true,
+		},
 	}
 
 	for _, test := range tests {