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 * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

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 *

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package com.sun.tools.javac.code;

import com.sun.tools.javac.code.Lint.LintCategory;

import com.sun.tools.javac.code.Source.Feature;

import com.sun.tools.javac.jvm.Target;

import com.sun.tools.javac.resources.CompilerProperties.Errors;

import com.sun.tools.javac.resources.CompilerProperties.Warnings;

import com.sun.tools.javac.util.Assert;

import com.sun.tools.javac.util.Context;

import com.sun.tools.javac.util.JCDiagnostic.DiagnosticPosition;

import com.sun.tools.javac.util.JCDiagnostic.Error;

import com.sun.tools.javac.util.JCDiagnostic.SimpleDiagnosticPosition;

import com.sun.tools.javac.util.Options;

import javax.tools.JavaFileObject;

import java.util.HashMap;

import java.util.Map;

import static com.sun.tools.javac.main.Option.PREVIEW;

/**

 * Helper class to handle preview language features. This class maps certain language features

 * (see {@link Feature} into 'preview' features; the mapping is completely ad-hoc, so as to allow

 * for maximum flexibility, which allows to migrate preview feature into supported features with ease.

 *

 * This class acts as a centralized point against which usages of preview features are reported by

 * clients (e.g. other javac classes). Internally, this class collects all such usages and generates

 * diagnostics to inform the user of such usages. Such diagnostics can be enabled using the

 * {@link LintCategory#PREVIEW} lint category, and are suppressible by usual means.

 */

public class Preview {

    private final boolean enabled;

    /** test flag: should all features be considered as preview features? */

    private final boolean forcePreview;

    /** a mapping from classfile numbers to Java SE versions */

    private final Map<Integer, Source> majorVersionToSource;

    private static final Context.Key<Preview> previewKey = new Context.Key<>();

    public static Preview instance(Context context) {

        Preview instance = context.get(previewKey);

        if (instance == null) {

            instance = new Preview(context);

        }

        return instance;

    }

    Preview(Context context) {

        context.put(previewKey, this);

        Options options = Options.instance(context);

        enabled = options.isSet(PREVIEW);

        forcePreview = options.isSet("forcePreview");

        majorVersionToSource = initMajorVersionToSourceMap();

    }

    private Map<Integer, Source> initMajorVersionToSourceMap() {

        Map<Integer, Source> majorVersionToSource = new HashMap<>();

        for (Target t : Target.values()) {

            int major = t.majorVersion;

            Source source = Source.lookup(t.name);

            if (source != null) {

                majorVersionToSource.put(major, source);

            }

        }

        return majorVersionToSource;

   }

    /**

     * Report usage of a preview feature. Usages reported through this method will affect the

     * set of sourcefiles with dependencies on preview features.

     * @param pos the position at which the preview feature was used.

     * @param feature the preview feature used.

     */

    public void warnPreview(int pos, Feature feature) {

        warnPreview(new SimpleDiagnosticPosition(pos), feature);

    }

    /**

     * Report usage of a preview feature. Usages reported through this method will affect the

     * set of sourcefiles with dependencies on preview features.

     * @param pos the position at which the preview feature was used.

     * @param feature the preview feature used.

     */

    public void warnPreview(DiagnosticPosition pos, Feature feature) {

        Assert.check(isEnabled());

        Assert.check(isPreview(feature));

                    Warnings.PreviewFeatureUsePlural(feature.nameFragment()) :

                    Warnings.PreviewFeatureUse(feature.nameFragment()));

    }

    /**

     * Report usage of a preview feature in classfile.

     * @param classfile the name of the classfile with preview features enabled

     * @param majorVersion the major version found in the classfile.

     */

    public void warnPreview(JavaFileObject classfile, int majorVersion) {

        Assert.check(isEnabled());

                    Warnings.PreviewFeatureUseClassfile(classfile, majorVersionToSource.get(majorVersion).name));

    }

    /**

     * Are preview features enabled?

     * @return true, if preview features are enabled.

     */

    public boolean isEnabled() {

        return enabled;

    }

    /**

     * Is given feature a preview feature?

     * @param feature the feature to be tested.

     * @return true, if given feature is a preview feature.

     */

    public boolean isPreview(Feature feature) {

        if (feature == Feature.SWITCH_EXPRESSION ||

            feature == Feature.SWITCH_MULTIPLE_CASE_LABELS ||

            feature == Feature.SWITCH_RULE ||

            feature == Feature.TEXT_BLOCKS)

            return true;

        //Note: this is a backdoor which allows to optionally treat all features as 'preview' (for testing).

        //When real preview features will be added, this method can be implemented to return 'true'

        //for those selected features, and 'false' for all the others.

        return forcePreview;

    }

    /**

     * Generate an error key which captures the fact that a given preview feature could not be used

     * due to the preview feature support being disabled.

     * @param feature the feature for which the diagnostic has to be generated.

     * @return the diagnostic.

     */

    public Error disabledError(Feature feature) {

        Assert.check(!isEnabled());

        return feature.isPlural() ?

                Errors.PreviewFeatureDisabledPlural(feature.nameFragment()) :

                Errors.PreviewFeatureDisabled(feature.nameFragment());

    }

    /**

     * Generate an error key which captures the fact that a preview classfile cannot be loaded

     * due to the preview feature support being disabled.

     * @param classfile the name of the classfile with preview features enabled

     * @param majorVersion the major version found in the classfile.

     */

    public Error disabledError(JavaFileObject classfile, int majorVersion) {

        Assert.check(!isEnabled());

        return Errors.PreviewFeatureDisabledClassfile(classfile, majorVersionToSource.get(majorVersion).name);

    }

}