[Bug]: NPE when a variable from a structured binding pattern is used in an anonymous function expression

[MaryamZi]

Description

$title.

Steps to Reproduce

type Doctor record {
    string name;
    string category;    
};

function addDoctor(Doctor doctor, string[] categories) returns error? {
    var {category} = doctor; // also getting an unused variable warning
    if !categories.some(
        existingCategory => existingCategory == category) {
        
    }
}

or

type Doctor record {
    string name;
    string category;    
};

function addDoctor(Doctor doctor, string[] categories) returns error? {
    var {category} = doctor; // also getting an unused variable warning
    if !some(categories, existingCategory => existingCategory == category) {
        
    }
}

function some(string[] arr, function (string s) returns boolean func) returns boolean {
    foreach string item in arr {
        if func(item) {
            return true;
        }
    }
    return false;
}

[2023-08-18 09:22:48,015] SEVERE {b7a.log.crash} - null 
java.lang.NullPointerException
        at org.wso2.ballerinalang.compiler.bir.codegen.JvmInstructionGen.getJVMIndexOfVarRef(JvmInstructionGen.java:1323)
        at org.wso2.ballerinalang.compiler.bir.codegen.JvmInstructionGen.loadVar(JvmInstructionGen.java:2141)
        at org.wso2.ballerinalang.compiler.bir.codegen.JvmInstructionGen.generateFPLoadIns(JvmInstructionGen.java:1760)
        at org.wso2.ballerinalang.compiler.bir.codegen.JvmInstructionGen.generateInstructions(JvmInstructionGen.java:2336)
        at org.wso2.ballerinalang.compiler.bir.codegen.JvmCodeGenUtil.getLastScopeFromBBInsGen(JvmCodeGenUtil.java:591)
        at org.wso2.ballerinalang.compiler.bir.codegen.methodgen.MethodGen.generateBasicBlocks(MethodGen.java:558)
        at org.wso2.ballerinalang.compiler.bir.codegen.methodgen.MethodGen.genJMethodForBFunc(MethodGen.java:274)
        at org.wso2.ballerinalang.compiler.bir.codegen.methodgen.MethodGen.generateMethod(MethodGen.java:175)
        at org.wso2.ballerinalang.compiler.bir.codegen.JvmPackageGen.lambda$generateModuleClasses$0(JvmPackageGen.java:433)
        at java.base/java.util.HashMap.forEach(HashMap.java:1337)
        at org.wso2.ballerinalang.compiler.bir.codegen.JvmPackageGen.generateModuleClasses(JvmPackageGen.java:388)
        at org.wso2.ballerinalang.compiler.bir.codegen.JvmPackageGen.generate(JvmPackageGen.java:800)
        at org.wso2.ballerinalang.compiler.bir.codegen.CodeGenerator.generate(CodeGenerator.java:101)
        at org.wso2.ballerinalang.compiler.bir.codegen.CodeGenerator.generate(CodeGenerator.java:72)
        at io.ballerina.projects.JBallerinaBackend.performCodeGen(JBallerinaBackend.java:321)
        at io.ballerina.projects.ModuleContext.generateCodeInternal(ModuleContext.java:480)
        at io.ballerina.projects.ModuleCompilationState$4.generatePlatformSpecificCode(ModuleCompilationState.java:132)
        at io.ballerina.projects.ModuleContext.generatePlatformSpecificCode(ModuleContext.java:387)
        at io.ballerina.projects.JBallerinaBackend.performCodeGen(JBallerinaBackend.java:173)
        at io.ballerina.projects.JBallerinaBackend.<init>(JBallerinaBackend.java:142)
        at io.ballerina.projects.JBallerinaBackend.lambda$from$0(JBallerinaBackend.java:120)
        at java.base/java.util.HashMap.computeIfAbsent(HashMap.java:1134)
        at io.ballerina.projects.PackageCompilation.getCompilerBackend(PackageCompilation.java:172)
        at io.ballerina.projects.JBallerinaBackend.from(JBallerinaBackend.java:119)
        at io.ballerina.cli.task.CompileTask.execute(CompileTask.java:201)
        at io.ballerina.cli.TaskExecutor.executeTasks(TaskExecutor.java:40)
        at io.ballerina.cli.cmd.BuildCommand.execute(BuildCommand.java:288)
        at java.base/java.util.Optional.ifPresent(Optional.java:183)
        at io.ballerina.cli.launcher.Main.main(Main.java:56)

Affected Version(s)

2201.7.1

OS, DB, other environment details and versions

No response

Related area

-> Compilation

Related issue(s) (optional)

No response

Suggested label(s) (optional)

No response

Suggested assignee(s) (optional)

No response

[chiranSachintha]

type Doctor record {
    string name;
    string category;
};

function addDoctor(Doctor doctor, string[] categories) {
    var {category} = doctor;
    var addCategory = function() {
        _ = category;
    };
}

When considering the above example, we desugared it as follows:

type Doctor record {
    string name;
    string category;
};

function addDoctor(Doctor doctor, string[] categories) {
    {
        map<(any|error)> recordVar_1 = <map<(any|error)>> doctor;
        string category = <string> recordVar_1["category"];
    }
    
    var addCategory = function() {
        _ = category;
    };
}

Since we added category variable to a block scope, we can't access category within the function scope. In the above example, after desugaring, we use category in the lambda scope, but there is no way to access category because it is defined in the block scope. So IMO, we should address this issue in the desugaring phase.

[github-actions]

This issue is NOT closed with a proper Reason/ label. Make sure to add proper reason label before closing. Please add or leave a comment with the proper reason label now.

      - Reason/EngineeringMistake - The issue occurred due to a mistake made in the past.
      - Reason/Regression - The issue has introduced a regression.
      - Reason/MultipleComponentInteraction - Issue occured due to interactions in multiple components.
      - Reason/Complex - Issue occurred due to complex scenario.
      - Reason/Invalid - Issue is invalid.
      - Reason/Other - None of the above cases.