Add `@CanIgnoreReturnValue` as appropriate to Gson methods. #2369

eamonnmcmanus · 2023-04-10T17:28:56Z

This annotation indicates that the return value of the annotated method does not need to be used. If it is not present on a non-void method, and if Error Prone's CheckReturnValue is active, then calling the method without using the result is an error. However, we are not enabling CheckReturnValue by default here.

Also update some code that does ignore return values, so that the returned value is used, if only by assigning it to an unused variable.

This annotation indicates that return value of the annotated method does not need to be used. If it is _not_ present on a non-void method, and if Error Prone's `CheckReturnValue` is active, then calling the method without using the result is an error. However, we are not enabling `CheckReturnValue` by default here. Also update some code that does ignore return values, so that the returned value is used, if only by assigning it to an unused variable.

gson/src/main/java/com/google/gson/stream/JsonReader.java

@@ -1664,7 +1664,7 @@
   */
  private void consumeNonExecutePrefix() throws IOException {
    // fast forward through the leading whitespace
-    nextNonWhitespace(true);
+    int unused = nextNonWhitespace(true);


gson/src/main/java/com/google/gson/Gson.java

@@ -1223,7 +1223,7 @@
    boolean oldLenient = reader.isLenient();
    reader.setLenient(true);
    try {
-      reader.peek();
+      JsonToken unused = reader.peek();


gson/src/main/java/com/google/gson/internal/Streams.java

@@ -44,7 +45,7 @@
  public static JsonElement parse(JsonReader reader) throws JsonParseException {
    boolean isEmpty = true;
    try {
-      reader.peek();
+      JsonToken unused = reader.peek();


gson/src/main/java/com/google/gson/stream/JsonReader.java

@@ -1119,7 +1119,7 @@
          return;
        } else if (c == '\\') {
          pos = p;
-          readEscapeCharacter();
+          char unused = readEscapeCharacter();


kluever

LGTM

Marcono1234

I hope it is ok that I added a few review comments.

However, we are not enabling CheckReturnValue by default here.

Do you mean with this, that if users were using Error Prone they would not see any warnings? Would it be necessary to add @CheckReturnValue to the package-info.java files of Gson to achieve that (as hinted by the @CanIgnoreReturnValue documentation)?

Marcono1234 · 2023-04-10T19:44:28Z

gson/src/main/java/com/google/gson/JsonStreamParser.java

@@ -15,6 +15,7 @@
 */
 package com.google.gson;

+import com.google.errorprone.annotations.CanIgnoreReturnValue;


Marcono1234 · 2023-04-10T19:48:33Z

gson/src/main/java/com/google/gson/JsonElement.java

+  @CanIgnoreReturnValue
  public JsonNull getAsJsonNull() {


Maybe there should be a comment explaining this? E.g.

@CanIgnoreReturnValue // For when this method is used only to verify that the value is JsonNull

That's fair. I had to do the var unused = ... in a few places in Google's source code that were for example calling getAsBoolean() to check that it was indeed a Boolean and not something else. Here there's basically no other reason to call it, since it can only ever return JsonNull.INSTANCE.

Marcono1234 · 2023-04-10T19:54:32Z

gson/src/test/java/com/google/gson/functional/DefaultTypeAdaptersTest.java

+    URL unused = gson.fromJson('"' + urlValue + '"', URL.class);
    assertThat(target.toExternalForm()).isEqualTo(urlValue);


This might actually be a bug in the test; that assertion is exactly the same as in line 128, without any of the values having changed. Should maybe be the following?

Suggested change

URL unused = gson.fromJson('"' + urlValue + '"', URL.class);

assertThat(target.toExternalForm()).isEqualTo(urlValue);

target = gson.fromJson('"' + urlValue + '"', URL.class);

assertThat(target.toExternalForm()).isEqualTo(urlValue);

Yes, I think you're right. Well spotted!

Marcono1234 · 2023-04-10T20:00:01Z

extras/src/test/java/com/google/gson/graph/GraphAdapterBuilderTest.java

+    Employee unused1 = new Employee("Jesse", google);
+    Employee unused2 = new Employee("Joel", google);


Might be good to add a comment here explaining this?

Suggested change

Employee unused1 = new Employee("Jesse", google);

Employee unused2 = new Employee("Joel", google);

// Employee constructor adds `this` to the given Company object

Employee unused1 = new Employee("Jesse", google);

Employee unused2 = new Employee("Joel", google);

eamonnmcmanus · 2023-04-10T20:11:08Z

Do you mean with this, that if users were using Error Prone they would not see any warnings? Would it be necessary to add @CheckReturnValue to the package-info.java files of Gson to achieve that (as hinted by the @CanIgnoreReturnValue documentation)?

Yes. People can enable this checking by compiling with -XepOpt:CheckReturnValue:Packages=com.google.gson. We could indeed add @CheckReturnValue to the various package-info.java files, and we might yet do that, but it could potentially be a bit intrusive. I've updated all of Google's internal source code to add the appropriate var unused = ... but I'm not sure I want to impose that on external users.

This annotation indicates that return value of the annotated method does not need to be used. If it is _not_ present on a non-void method, and if Error Prone's `CheckReturnValue` is active, then calling the method without using the result is an error. However, we are not enabling `CheckReturnValue` by default here. Also update some code that does ignore return values, so that the returned value is used, if only by assigning it to an unused variable.

) This annotation indicates that return value of the annotated method does not need to be used. If it is _not_ present on a non-void method, and if Error Prone's `CheckReturnValue` is active, then calling the method without using the result is an error. However, we are not enabling `CheckReturnValue` by default here. Also update some code that does ignore return values, so that the returned value is used, if only by assigning it to an unused variable.

github-advanced-security bot found potential problems Apr 10, 2023

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eamonnmcmanus requested a review from kluever April 10, 2023 17:32

kluever approved these changes Apr 10, 2023

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eamonnmcmanus merged commit c1da2d7 into google:master Apr 10, 2023

eamonnmcmanus deleted the cirv branch April 10, 2023 17:50

Marcono1234 reviewed Apr 10, 2023

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Add `@CanIgnoreReturnValue` as appropriate to Gson methods. #2369

Add `@CanIgnoreReturnValue` as appropriate to Gson methods. #2369

eamonnmcmanus commented Apr 10, 2023 •

edited

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eamonnmcmanus Apr 10, 2023

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eamonnmcmanus commented Apr 10, 2023

		URL unused = gson.fromJson('"' + urlValue + '"', URL.class);
		assertThat(target.toExternalForm()).isEqualTo(urlValue);

		Employee unused1 = new Employee("Jesse", google);
		Employee unused2 = new Employee("Joel", google);

Add @CanIgnoreReturnValue as appropriate to Gson methods. #2369

Add @CanIgnoreReturnValue as appropriate to Gson methods. #2369

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eamonnmcmanus commented Apr 10, 2023

Add `@CanIgnoreReturnValue` as appropriate to Gson methods. #2369

Add `@CanIgnoreReturnValue` as appropriate to Gson methods. #2369

eamonnmcmanus commented Apr 10, 2023 •

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Marcono1234 Apr 10, 2023 •

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