[libcalamares] Refactor target-environment calls

- Add a more general targetEnvCommand() that returns both
   error code and process output.
 - Change existing targetEnvCall() and targetEnvOutput()
   to use general form while discarding some data.

src/libcalamares/utils/CalamaresUtilsSystem.cpp

@@ -92,42 +92,14 @@ System::mount( const QString& devicePath,
     return QProcess::execute( program, args );
 }
 
-int
-System::targetEnvCall( const QStringList& args,
-            const QString& workingPath,
-            const QString& stdInput,
-            int timeoutSec )
-{
-    QString discard;
-    return targetEnvOutput( args,
-                         discard,
-                         workingPath,
-                         stdInput,
-                         timeoutSec );
-}
-
-
-int
-System::targetEnvCall( const QString& command,
-            const QString& workingPath,
-            const QString& stdInput,
-            int timeoutSec )
-{
-    return targetEnvCall( QStringList{ command },
-                       workingPath,
-                       stdInput,
-                       timeoutSec );
-}
-
-
-int
-System::targetEnvOutput( const QStringList& args,
-              QString& output,
-              const QString& workingPath,
-              const QString& stdInput,
-              int timeoutSec )
+ProcessResult
+System::targetEnvCommand(
+    const QStringList& args,
+    const QString& workingPath,
+    const QString& stdInput,
+    int timeoutSec )
 {
-    output.clear();
+    QString output;
 
     if ( !Calamares::JobQueue::instance() )
         return -3;
@@ -212,22 +184,7 @@ System::targetEnvOutput( const QStringList& args,
         cLog() << "Target cmd:" << args;
         cLog().noquote() << "Target output:\n" << output;
     }
-    return r;
-}
-
-
-int
-System::targetEnvOutput( const QString& command,
-              QString& output,
-              const QString& workingPath,
-              const QString& stdInput,
-              int timeoutSec )
-{
-    return targetEnvOutput( QStringList{ command },
-                         output,
-                         workingPath,
-                         stdInput,
-                         timeoutSec );
+    return ProcessResult(r, output);
 }
 
 

src/libcalamares/utils/CalamaresUtilsSystem.h

@@ -21,10 +21,18 @@
 #include "DllMacro.h"
 
 #include <QObject>
+#include <QPair>
 #include <QString>
 
 namespace CalamaresUtils
 {
+class ProcessResult : public QPair< int, QString >
+{
+public:
+    /** @brief Implicit one-argument constructor has no output, only a return code */
+    ProcessResult( int r ) : QPair< int, QString >( r, QString() ) {}
+    ProcessResult( int r, QString s ) : QPair< int, QString >( r, s ) {}
+} ;
 
 /**
  * @brief The System class is a singleton with utility functions that perform
@@ -61,42 +69,75 @@ public:
                          const QString& filesystemName = QString(),
                          const QString& options = QString() );
 
+
     /**
       * Runs the specified command in the chroot of the target system.
-      * @param args the call with arguments, as a string list.
+      * @param args the command with arguments, as a string list.
       * @param workingPath the current working directory for the QProcess
       * call (optional).
       * @param stdInput the input string to send to the running process as
       * standard input (optional).
       * @param timeoutSec the timeout after which the process will be
       * killed (optional, default is 0 i.e. no timeout).
-      * @returns the program's exit code, or:
+      *
+      * @returns the program's exit code and its output (if any). Special
+      *     exit codes (which will never have any output) are:
       *             -1 = QProcess crash
       *             -2 = QProcess cannot start
       *             -3 = bad arguments
       *             -4 = QProcess timeout
       */
-    DLLEXPORT int targetEnvCall( const QStringList& args,
+    DLLEXPORT ProcessResult targetEnvCommand(
+        const QStringList &args,
+        const QString& workingPath = QString(),
+        const QString& stdInput = QString(),
+        int timeoutSec = 0 );
+
+    /** @brief Convenience wrapper for targetEnvCommand() which returns only the exit code */
+    inline int targetEnvCall( const QStringList& args,
                               const QString& workingPath = QString(),
                               const QString& stdInput = QString(),
-                              int timeoutSec = 0 );
+                              int timeoutSec = 0 )
+    {
+        return targetEnvCommand( args, workingPath, stdInput, timeoutSec ).first;
+    }
 
-    DLLEXPORT int targetEnvCall( const QString& command,
+    /** @brief Convenience wrapper for targetEnvCommand() which returns only the exit code */
+    inline int targetEnvCall( const QString& command,
                               const QString& workingPath = QString(),
                               const QString& stdInput = QString(),
-                              int timeoutSec = 0 );
+                              int timeoutSec = 0 )
+    {
+        return targetEnvCall( QStringList{ command }, workingPath, stdInput, timeoutSec );
+    }
 
-    DLLEXPORT int targetEnvOutput( const QStringList& args,
+    /** @brief Convenience wrapper for targetEnvCommand() which returns only the exit code
+     *
+     * Places the called program's output in the @p output string.
+     */
+    int targetEnvOutput( const QStringList& args,
                                 QString& output,
                                 const QString& workingPath = QString(),
                                 const QString& stdInput = QString(),
-                                int timeoutSec = 0 );
-
-    DLLEXPORT int targetEnvOutput( const QString& command,
+                                int timeoutSec = 0 )
+    {
+        auto r = targetEnvCommand( args, workingPath, stdInput, timeoutSec );
+        output = r.second;
+        return r.first;
+    }
+
+    /** @brief Convenience wrapper for targetEnvCommand() which returns only the exit code
+     *
+     * Places the called program's output in the @p output string.
+     */
+    inline int targetEnvOutput( const QString& command,
                                 QString& output,
                                 const QString& workingPath = QString(),
                                 const QString& stdInput = QString(),
-                                int timeoutSec = 0 );
+                                int timeoutSec = 0 )
+    {
+        return targetEnvOutput( QStringList{ command }, output, workingPath, stdInput, timeoutSec );
+    }
 
     /**
      * @brief getTotalMemoryB returns the total main memory, in bytes.