ToArray.java

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import org.checkerframework.checker.nullness.qual.*;

public class ToArray {
    private List<@Nullable String> nullableList = new ArrayList<@Nullable String>();
    private List<@NonNull String> nonnullList = new ArrayList<@NonNull String>();

    void listToArrayObject() {
        for (@Nullable Object o : nullableList.toArray()) ;
        //:: error: (enhancedfor.type.incompatible)
        for (@NonNull Object o : nullableList.toArray()) ; // error

        for (@Nullable Object o : nonnullList.toArray()) ;
        for (@NonNull Object o : nonnullList.toArray()) ;
    }

    void listToArrayE() {
        for (@Nullable String o : nullableList.toArray(new @Nullable String[0])) ;
        //:: error: (enhancedfor.type.incompatible)
        for (@NonNull String o : nullableList.toArray(new @Nullable String[0])) ; // error
        //TODOINVARR:: error: (argument.type.incompatible)
        for (@Nullable String o : nullableList.toArray(new @NonNull String[0])) ;
        //TODOINVARR:: error: (argument.type.incompatible)
        //:: error: (enhancedfor.type.incompatible)
        for (@NonNull String o : nullableList.toArray(new @NonNull String[0])) ;

        for (@Nullable String o : nonnullList.toArray(new String[0])) ;
        // No error expected here. Note that the heuristics determine that the given array
        // is not used and that a new one will be created.
        for (@NonNull String o : nonnullList.toArray(new @Nullable String[0])) ;
        for (@Nullable String o : nonnullList.toArray(new @NonNull String[0])) ;
        for (@NonNull String o : nonnullList.toArray(new @NonNull String[0])) ;
    }

    private Collection<@Nullable String> nullableCol = new ArrayList<@Nullable String>();
    private Collection<@NonNull String> nonnullCol = new ArrayList<@NonNull String>();

    void colToArrayObject() {
        for (@Nullable Object o : nullableCol.toArray()) ;
        //:: error: (enhancedfor.type.incompatible)
        for (@NonNull Object o : nullableCol.toArray()) ; // error

        for (@Nullable Object o : nonnullCol.toArray()) ;
        for (@NonNull Object o : nonnullCol.toArray()) ;
    }

    void colToArrayE() {
        for (@Nullable String o : nullableCol.toArray(new @Nullable String[0])) ;
        //:: error: (enhancedfor.type.incompatible)
        for (@NonNull String o : nullableCol.toArray(new @Nullable String[0])) ; // error
        //TODOINVARR:: error: (argument.type.incompatible)
        for (@Nullable String o : nullableCol.toArray(new @NonNull String[0])) ;
        //TODOINVARR:: error: (argument.type.incompatible)
        //:: error: (enhancedfor.type.incompatible)
        for (@NonNull String o : nullableCol.toArray(new @NonNull String[0])) ; // error

        for (@Nullable String o : nonnullCol.toArray(new String[0])) ;
        // No error expected here. Note that the heuristics determine that the given array
        // is not used and that a new one will be created.
        for (@NonNull String o : nonnullCol.toArray(new @Nullable String[0])) ;
        for (@Nullable String o : nonnullCol.toArray(new @NonNull String[0])) ;
        for (@NonNull String o : nonnullCol.toArray(new @NonNull String[0])) ;
    }

    void testHearusitics() {
        for (@Nullable String o : nonnullCol.toArray(new String[] {})) ;
        for (@NonNull String o : nonnullCol.toArray(new String[] {})) ;
        for (@Nullable String o : nonnullCol.toArray(new String[0])) ;
        for (@NonNull String o : nonnullCol.toArray(new String[0])) ;
        for (@Nullable String o : nonnullCol.toArray(new String[nonnullCol.size()])) ;
        for (@NonNull String o : nonnullCol.toArray(new String[nonnullCol.size()])) ;

        for (@Nullable String o : nonnullCol.toArray(new @Nullable String[] {null})) ;
        //:: error: (enhancedfor.type.incompatible)
        for (@NonNull String o : nonnullCol.toArray(new @Nullable String[] {null})) ; // error
        // Size 1 is too big for an empty array. Complain. TODO: Could allow as result is Nullable.
        //:: error: (new.array.type.invalid)
        for (@Nullable String o : nonnullCol.toArray(new String[1])) ;
        //:: error: (enhancedfor.type.incompatible) :: error: (new.array.type.invalid)
        for (@NonNull String o : nonnullCol.toArray(new String[1])) ; // error
        // Array too big -> complain. TODO: Could allow as result is Nullable.
        //:: error: (new.array.type.invalid)
        for (@Nullable String o : nonnullCol.toArray(new String[nonnullCol.size() + 1])) ;
        // Array too big -> complain.
        //:: error: (enhancedfor.type.incompatible) :: error: (new.array.type.invalid)
        for (@NonNull String o : nonnullCol.toArray(new String[nonnullCol.size() + 1])) ; // error

        // cannot handle the following cases for now
        // new array not size 0 or .size -> complain about cration. TODO: Could allow as result is Nullable.
        //:: error: (new.array.type.invalid)
        for (@Nullable String o : nonnullCol.toArray(new String[nonnullCol.size() - 1])) ;
        // New array not size 0 or .size -> complain about creation.
        //:: error: (enhancedfor.type.incompatible) :: error: (new.array.type.invalid)
        for (@NonNull String o : nonnullCol.toArray(new String[nonnullCol.size() - 1])) ; // error
    }
}