package com.simpleplugin;

import com.intellij.lang.cacheBuilder.DefaultWordsScanner;
import com.intellij.lang.cacheBuilder.WordsScanner;
import com.intellij.lang.findUsages.FindUsagesProvider;
import com.intellij.psi.PsiElement;
import com.intellij.psi.PsiNamedElement;
import com.intellij.psi.tree.TokenSet;
import com.simpleplugin.psi.SimpleProperty;
import com.simpleplugin.psi.SimpleTypes;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

public class SimpleFindUsagesProvider implements FindUsagesProvider {
    @Nullable
    @Override
    public WordsScanner getWordsScanner() {
        return new DefaultWordsScanner(new SimpleLexerAdapter(),
                    TokenSet.create(SimpleTypes.KEY), TokenSet.create(SimpleTypes.COMMENT), TokenSet.EMPTY);;
    }

    @Override
    public boolean canFindUsagesFor(@NotNull PsiElement psiElement) {
        return psiElement instanceof PsiNamedElement;
    }

    @Nullable
    @Override
    public String getHelpId(@NotNull PsiElement psiElement) {
        return null;
    }

    @NotNull
    @Override
    public String getType(@NotNull PsiElement element) {
        if (element instanceof SimpleProperty) {
            return "simple property";
        } else {
            return "";
        }
    }

    @NotNull
    @Override
    public String getDescriptiveName(@NotNull PsiElement element) {
        if (element instanceof SimpleProperty) {
            return ((SimpleProperty) element).getKey();
        } else {
            return "";
        }
    }

    @NotNull
    @Override
    public String getNodeText(@NotNull PsiElement element, boolean useFullName) {
        if (element instanceof SimpleProperty) {
            return ((SimpleProperty) element).getKey() + ":" + ((SimpleProperty) element).getValue();
        } else {
            return "";
        }
    }
}

package com.simpleplugin;

import com.intellij.lang.cacheBuilder.DefaultWordsScanner;
import com.intellij.lang.cacheBuilder.WordsScanner;
import com.intellij.lang.findUsages.FindUsagesProvider;
import com.intellij.psi.PsiElement;
import com.intellij.psi.PsiNamedElement;
import com.intellij.psi.tree.TokenSet;
import com.simpleplugin.psi.SimpleProperty;
import com.simpleplugin.psi.SimpleTypes;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

public class SimpleFindUsagesProvider implements FindUsagesProvider {
    @Nullable
    @Override
    public WordsScanner getWordsScanner() {
        return new DefaultWordsScanner(new SimpleLexerAdapter(),
                    TokenSet.create(SimpleTypes.KEY), TokenSet.create(SimpleTypes.COMMENT), TokenSet.EMPTY);
    }

    @Override
    public boolean canFindUsagesFor(@NotNull PsiElement psiElement) {
        return psiElement instanceof PsiNamedElement;
    }

    @Nullable
    @Override
    public String getHelpId(@NotNull PsiElement psiElement) {
        return null;
    }

    @NotNull
    @Override
    public String getType(@NotNull PsiElement element) {
        if (element instanceof SimpleProperty) {
            return "simple property";
        } else {
            return "";
        }
    }

    @NotNull
    @Override
    public String getDescriptiveName(@NotNull PsiElement element) {
        if (element instanceof SimpleProperty) {
            return ((SimpleProperty) element).getKey();
        } else {
            return "";
        }
    }

    @NotNull
    @Override
    public String getNodeText(@NotNull PsiElement element, boolean useFullName) {
        if (element instanceof SimpleProperty) {
            return ((SimpleProperty) element).getKey() + ":" + ((SimpleProperty) element).getValue();
        } else {
            return "";
        }
    }
}

Fix compiler error