JaCoCo 0.8.14 version reduces the test coverage results for switch statement (parameter type String) when used with forEach

[Sofiya-Sundaramoorthy]

JaCoCo version: 0.8.14 JDK version: 25 OS: Mac Tools: Maven Github: https://github.com/Sofiya-Sundaramoorthy/jacoco-0.8.14-switch-statement Brief description: When upgrading the JaCoCo version from 0.8.12 to 0.8.14 to support JDK25 upgrades, I noticed that the test coverage dropped for a switch statement in combination with forEach.

checkData method takes List<String> as parameter which then loops using forEach to pass data to a switch statement

// method

protected String checkData(List<String> datas) {
        datas.forEach(data -> {
            switch(data) {
                case "a" -> System.out.println("first data");
                case "b" -> System.out.println("second data");
                case "c" -> System.out.println("third data");
                default -> System.out.println("default data");
            };
        });
        return null;
    };

//testcase

@Test
	void testData() {
		var application = new SwitchStatementApplication();
		var result1 = application.checkData(List.of("a", "b", "c", "d"));
		assertNull(result1);
	}

The minimal reproducible code is in the github repo https://github.com/Sofiya-Sundaramoorthy/jacoco-0.8.14-switch-statement

Note: The switch statement takes parameter of type String which gives 78% test coverage. However, when passing parameter type of Int the coverage is 100%

Expected behaviour: The combination of forEach + switch (parameter type as String) should produce 100% test coverage

Actual behaviour: The combination of forEach + switch (parameter type as String) produces 78% test coverage

Please refer the screenshots

JaCoCo 0.8.12 with JDK21

JaCoCo 0.8.14 with JDK25

[Godin]

First of all thank you for the reproducer! ❤️

---

Should be noted that this is not a regression in JaCoCo, but change in javac compiler in JDK 24:

for src/Example.java

import java.util.List;

public class Example {
    String checkData(List<String> datas) {
        datas.forEach(data -> {
            switch(data) {
                case "a" -> System.out.println("first data");
                case "b" -> System.out.println("second data");
                case "c" -> System.out.println("third data");
                default -> System.out.println("default data");
            };
        });
        return null;
    };

    public static void main(String[] args) {
        new Example().checkData(List.of("a", "b", "c", "d"));
    }
}

using JaCoCo version 0.8.12 execution of

javac --release 21 -g -d classes src/Example.java
java  -javaagent:jacoco-0.8.12/lib/jacocoagent.jar -cp classes Example
java -jar jacoco-0.8.12/lib/jacococli.jar \
    report jacoco.exec \
    --classfiles classes \
    --sourcefiles src \
    --html report

with javac 23.0.2 produces expected result

All 4 branches covered.

whereas with javac 24.0.2 produces unexpected result

3 of 14 branches missed.

For these two versions execution of

javap -v -p classes/Example.class

produces two different outputs

       LocalVariableTable:
         Start  Length  Slot  Name   Signature
+            2     143     1   s0$   Ljava/lang/String;
+            4     141     2 tmp1$   I
             0     146     0  data   Ljava/lang/String;

showing change of LocalVariableTable in method lambda$checkData$0 that contains body of the lambda.

Which affects

https://github.com/jacoco/jacoco/blob/2eb248366f0eb63fd964fc7a81804b27229a6edd/org.jacoco.core/src/org/jacoco/core/internal/analysis/filter/StringSwitchJavacFilter.java#L60-L62