Meson build plugin initial support

Most basic project management is implemented:
- Project config/build
- Build options accessible to user
- Lists most build targets
- Meson and Ninja added to kit setup
- Basic project file tree with files known by Meson
- Some basic meson and ninja process output parsing
- Some project templates

Missing features, that will come later:
- Configurable project tree layout
- Locators for Meson
- Build importer
- Access to Machine files for better user fine tuning
- ...

Fixes: QTCREATORBUG-18117
Change-Id: I2811e71562c113fb0fc6b6177bcf0698fa71ef63
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/mesonprojectmanager/project/projecttree/projecttree.cpp

@@ -0,0 +1,95 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 Alexis Jeandet.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+#include "projecttree.h"
+#include <set>
+namespace MesonProjectManager {
+namespace Internal {
+ProjectTree::ProjectTree() {}
+
+void buildTargetTree(std::unique_ptr<MesonProjectNode> &root, const Target &target)
+{
+    const auto path = Utils::FilePath::fromString(target.definedIn);
+    for (const auto &group : target.sources) {
+        for (const auto &file : group.sources) {
+            root->addNestedNode(
+                std::make_unique<ProjectExplorer::FileNode>(Utils::FilePath::fromString(file),
+                                                            ProjectExplorer::FileType::Source));
+        }
+    }
+}
+
+void addTargetNode(std::unique_ptr<MesonProjectNode> &root, const Target &target)
+{
+    root->findNode([&target, path = Utils::FilePath::fromString(target.definedIn)](
+                       ProjectExplorer::Node *node) {
+        if (node->filePath() == path.absolutePath()) {
+            auto asFolder = dynamic_cast<ProjectExplorer::FolderNode *>(node);
+            if (asFolder) {
+                auto targetNode = std::make_unique<MesonTargetNode>(path.absolutePath().pathAppended(
+                                                                        target.name),
+                                                                    Target::fullName(target));
+                targetNode->setDisplayName(target.name);
+                asFolder->addNode(std::move(targetNode));
+            }
+            return true;
+        }
+        return false;
+    });
+}
+
+void addOptionsFile(std::unique_ptr<MesonProjectNode> &project)
+{
+    auto meson_options = project->filePath().pathAppended("meson_options.txt");
+    if (meson_options.exists())
+        project->addNestedNode(
+            std::make_unique<ProjectExplorer::FileNode>(meson_options,
+                                                        ProjectExplorer::FileType::Project));
+}
+
+std::unique_ptr<MesonProjectNode> ProjectTree::buildTree(const Utils::FilePath &srcDir,
+                                                         const TargetsList &targets,
+                                                         const std::vector<Utils::FilePath> &bsFiles)
+{
+    using namespace ProjectExplorer;
+    std::set<Utils::FilePath> targetPaths;
+    auto root = std::make_unique<MesonProjectNode>(srcDir);
+    std::for_each(std::cbegin(targets),
+                  std::cend(targets),
+                  [&root, &targetPaths](const Target &target) {
+                      buildTargetTree(root, target);
+                      targetPaths.insert(
+                          Utils::FilePath::fromString(target.definedIn).absolutePath());
+                      addTargetNode(root, target);
+                  });
+    for (Utils::FilePath bsFile : bsFiles) {
+        if (!bsFile.startsWith("/"))
+            bsFile = srcDir.pathAppended(bsFile.toString());
+        root->addNestedNode(
+            std::make_unique<ProjectExplorer::FileNode>(bsFile, ProjectExplorer::FileType::Project));
+    }
+    return root;
+}
+} // namespace Internal
+} // namespace MesonProjectManager