Utils: Add std::expected implementation

Adds a std::expected implementation that is compatible with >= C++11.

FilePath::fileContents and FilePath::writeFileContents as well as
FilePath::copyFile are changed to return std::expected.

A couple of macros have been added to aid in using the expected types.

An auto test was added showing how to use the library.

Change-Id: Ibe3aecfc1029a0cf13b45bf5184ff03a04a2393b
Reviewed-by: Eike Ziller <[email protected]>
Reviewed-by: Qt CI Bot <[email protected]>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libs/qmljs/qmljsmodelmanagerinterface.cpp b/src/libs/qmljs/qmljsmodelmanagerinterface.cpp
index 71bd55119be..9ba1d43fcf7 100644
--- a/src/libs/qmljs/qmljsmodelmanagerinterface.cpp
+++ b/src/libs/qmljs/qmljsmodelmanagerinterface.cpp
@@ -875,7 +875,7 @@ static bool findNewQmlLibraryInPath(const Utils::FilePath &path,
     }
 
     // found a new library!
-    const std::optional<QByteArray> contents = qmldirFile.fileContents();
+    const expected_str<QByteArray> contents = qmldirFile.fileContents();
     if (!contents)
         return false;
     QString qmldirData = QString::fromUtf8(*contents);
@@ -985,7 +985,7 @@ void ModelManagerInterface::parseLoop(QSet<Utils::FilePath> &scannedPaths,
             contents = entry.first;
             documentRevision = entry.second;
         } else {
-            const std::optional<QByteArray> fileContents = fileName.fileContents();
+            const expected_str<QByteArray> fileContents = fileName.fileContents();
             if (fileContents) {
                 QTextStream ins(*fileContents);
                 contents = ins.readAll();