[libcalamares] Document GS

- write apidox for all of GlobalStorage
- while here, polish up the SPDX bits

src/libcalamares/GlobalStorage.cpp

@@ -2,6 +2,7 @@
  *
  *   SPDX-FileCopyrightText: 2014-2015 Teo Mrnjavac <teo@kde.org>
  *   SPDX-FileCopyrightText: 2017-2018 Adriaan de Groot <groot@kde.org>
+ *   SPDX-License-Identifier: GPL-3.0-or-later
  *
  *   Calamares is free software: you can redistribute it and/or modify
  *   it under the terms of the GNU General Public License as published by
@@ -16,9 +17,6 @@
  *   You should have received a copy of the GNU General Public License
  *   along with Calamares. If not, see <http://www.gnu.org/licenses/>.
  *
- *   SPDX-License-Identifier: GPL-3.0-or-later
- *   License-Filename: LICENSE
- *
  */
 
 #include "GlobalStorage.h"

src/libcalamares/GlobalStorage.h

@@ -2,6 +2,7 @@
  *
  *   SPDX-FileCopyrightText: 2014-2015 Teo Mrnjavac <teo@kde.org>
  *   SPDX-FileCopyrightText: 2017-2018 Adriaan de Groot <groot@kde.org>
+ *   SPDX-License-Identifier: GPL-3.0-or-later
  *
  *   Calamares is free software: you can redistribute it and/or modify
  *   it under the terms of the GNU General Public License as published by
@@ -16,9 +17,6 @@
  *   You should have received a copy of the GNU General Public License
  *   along with Calamares. If not, see <http://www.gnu.org/licenses/>.
  *
- *   SPDX-License-Identifier: GPL-3.0-or-later
- *   License-Filename: LICENSE
- *
  */
 
 #ifndef CALAMARES_GLOBALSTORAGE_H
@@ -31,21 +29,65 @@
 namespace Calamares
 {
 
+/** @brief Storage for data that passes between Calamares modules.
+ *
+ * The Global Storage is global to the Calamars JobQueue and
+ * everything that depends on that: all of its modules use the
+ * same instance of the JobQueue, and so of the Global Storage.
+ *
+ * GS is used to pass data between modules; there is only convention
+ * about what keys are used, and individual modules should document
+ * what they put in to GS or what they expect to find in it.
+ *
+ * GS behaves as a basic key-value store, with a QVariantMap behind
+ * it. Any QVariant can be put into the storage, and the signal
+ * changed() is emitted when any data is modified.
+ *
+ * In general, see QVariantMap (possibly after calling data()) for details.
+ *
+ * This class is not thread-safe, but as long as JobQueue is, that's ok
+ * because only one module is active at a time.
+ */
 class GlobalStorage : public QObject
 {
     Q_OBJECT
 public:
+    /** @brief Create a GS object
+     *
+     * **Generally** there is only one GS object (hence, "global") which
+     * is owned by the JobQueue instance (which is a singleton). However,
+     * it is possible to create more GS objects.
+     */
     explicit GlobalStorage( QObject* parent = nullptr );
 
-    //NOTE: thread safety is guaranteed by JobQueue, which executes jobs one by one.
-    //      If at any time jobs become concurrent, this class must be made thread-safe.
+    /** @brief Insert a key and value into the store
+     *
+     * The @p value is added to the store with key @p key. If @p key
+     * already exists in the store, its existing value is overwritten.
+     * The changed() signal is emitted regardless.
+     */
     void insert( const QString& key, const QVariant& value );
+    /** @brief Removes a key and its value
+     *
+     * The @p key is removed from the store. If the @p key does not
+     * exist, nothing happens. changed() is emitted regardless.
+     *
+     * @return the number of keys remaining
+     */
     int remove( const QString& key );
 
-    /// @brief dump keys and values to the debug log
+    /** @brief dump keys and values to the debug log
+     *
+     * All the keys and their values are written to the debug log.
+     * See save() for caveats: this can leak sensitive information.
+     */
     void debugDump() const;
 
     /** @brief write as JSON to the given filename
+     *
+     * The file named @p filename is overwritten with a JSON representation
+     * of the entire global storage (this may be structured, for instance
+     * if maps or lists have been inserted).
      *
      * No tidying, sanitization, or censoring is done -- for instance,
      * the user module sets a slightly-obscured password in global storage,
@@ -58,7 +100,8 @@ public:
      *
      * No tidying, sanitization, or censoring is done.
      * The JSON file is read and each key is added as a value to
-     * the global storage.
+     * the global storage. The storage is not cleared first: existing
+     * keys will remain; keys that also occur in the JSON file are overwritten.
      */
     bool load( const QString& filename );
 
@@ -68,7 +111,10 @@ public:
      */
     bool saveYaml( const QString& filename );
 
-    /// @brief reads settings from the given filename
+    /** @brief reads settings from the given filename
+     *
+     * See also load(), above.
+     */
     bool loadYaml( const QString& filename );
 
     /** @brief Get internal mapping as a constant object
@@ -80,12 +126,41 @@ public:
     const QVariantMap& data() const { return m; }
 
 public Q_SLOTS:
+    /** @brief Does the store contain the given key?
+     *
+     * This can distinguish an explicitly-inserted QVariant() from
+     * a no-value-exists QVariant. See value() for details.
+     */
     bool contains( const QString& key ) const;
+    /** @brief The number of keys in the store
+     *
+     * This should be unsigned, but the underlying QMap uses signed as well.
+     * Equal to keys().length(), in theory.
+     */
     int count() const;
+    /** @brief The keys in the store
+     *
+     * This makes a copy of all the keys currently in the store, which
+     * could be used for iterating over all the values in the store.
+     */
     QStringList keys() const;
+    /** @brief Gets a value from the store
+     *
+     * If a value has been previously inserted, returns that value.
+     * If @p key does not exist in the store, returns a QVariant()
+     * (an invalid QVariant, which boolean-converts to false). Since
+     * QVariant() van also be inserted explicitly, use contains()
+     * to check for the presence of a key if you need that.
+     */
     QVariant value( const QString& key ) const;
 
 signals:
+    /** @brief Emitted any time the store changes
+     *
+     * Also emitted sometimes when the store does not change, e.g.
+     * when removing a non-existent key or inserting a value that
+     * is already present.
+     */
     void changed();
 
 private: