musrFT: fix the Fourier canvas on macOS and starting it from musredit.

- PFourierCanvas.h only forward declares PFourier. Including PFourier.h put
  fftw3.h into the dictionary payload, and cling (ROOT 6.40, macOS SDK 26+)
  fails on its '#include <stddef.h>', which lost the interpreter info of
  PFourierCanvas and with it all its signal/slot connections.
- musredit: run musrFT in the directory of the msr-file and write musrFT.log
  there. Started from the Finder/Dock the working directory is '/', the log
  cannot be written and QProcess refused to start musrFT. Merge stderr into
  the log, show the full command and the reason if starting fails.

src/classes/PFourierCanvas.cpp

@@ -37,6 +37,7 @@
 #include <TMath.h>
 #include <TGFileDialog.h>
 
+#include "PFourier.h"
 #include "PFourierCanvas.h"
 
 #include "icons/musrFT_icon.xpm"

src/include/PFourierCanvas.h

@@ -47,7 +47,12 @@
 #include <TLatex.h>
 
 #include "PMusr.h"
-#include "PFourier.h"
+
+// Only a forward declaration: PFourier.h pulls in fftw3.h, which would end up in
+// the dictionary payload parsed by cling at run time. On macOS (SDK 26+) cling
+// fails on its '#include <stddef.h>', which loses the interpreter info of
+// PFourierCanvas and with it all its signal/slot connections.
+class PFourier;
 
 // Canvas menu id's
 #define P_MENU_ID_FOURIER              10001

src/musredit_qt5/musredit/PTextEdit.cpp

@@ -2807,8 +2807,14 @@ void PTextEdit::musrFT()
   if (dlg->exec() == QDialog::Accepted) {
     fMusrFTPrevCmd = dlg->getMusrFTOptions();
     QProcess *proc = new QProcess(this);
-    proc->setStandardOutputFile("musrFT.log");
-    proc->setStandardErrorFile("musrFT.log");
+    // run musrFT in the directory of the msr-file. musredit started from the Finder/Dock
+    // has '/' as working directory, where the log-file cannot be written, and QProcess then
+    // refuses to start musrFT at all.
+    QFileInfo fi(*fFilenames.find(currentEditor()));
+    QString workDir = fi.exists() ? fi.absolutePath() : QDir::homePath();
+    proc->setWorkingDirectory(workDir);
+    proc->setProcessChannelMode(QProcess::MergedChannels);
+    proc->setStandardOutputFile(workDir + "/musrFT.log");
     QString cmd = fAdmin->getExecPath() + "/musrFT";
     QProcessEnvironment env = QProcessEnvironment::systemEnvironment();
 #if defined(Q_OS_DARWIN)
@@ -2820,12 +2826,14 @@ void PTextEdit::musrFT()
     proc->start(cmd, fMusrFTPrevCmd);
     if (!proc->waitForStarted()) {
       // error handling
-      QString msg(tr("Could not execute the output command: ")+cmd[0]);
+      QString msg(tr("Could not execute the output command: ")+cmd+"\n"+proc->errorString());
       QMessageBox::critical( nullptr,
                              tr("Fatal error"),
                              msg,
                              tr("Quit") );
-      return;
+      proc->deleteLater();
+    } else {
+      connect(proc, SIGNAL(finished(int,QProcess::ExitStatus)), proc, SLOT(deleteLater()));
     }
   }
 

src/musredit_qt6/musredit/PTextEdit.cpp

@@ -2910,8 +2910,14 @@ void PTextEdit::musrFT()
   if (dlg->exec() == QDialog::Accepted) {
     fMusrFTPrevCmd = dlg->getMusrFTOptions();
     QProcess *proc = new QProcess(this);
-    proc->setStandardOutputFile("musrFT.log");
-    proc->setStandardErrorFile("musrFT.log");
+    // run musrFT in the directory of the msr-file. musredit started from the Finder/Dock
+    // has '/' as working directory, where the log-file cannot be written, and QProcess then
+    // refuses to start musrFT at all.
+    QFileInfo fi(*fFilenames.find(currentEditor()));
+    QString workDir = fi.exists() ? fi.absolutePath() : QDir::homePath();
+    proc->setWorkingDirectory(workDir);
+    proc->setProcessChannelMode(QProcess::MergedChannels);
+    proc->setStandardOutputFile(workDir + "/musrFT.log");
     QString cmd = fAdmin->getExecPath() + "/musrFT";
     QProcessEnvironment env = QProcessEnvironment::systemEnvironment();
 #if defined(Q_OS_DARWIN)
@@ -2923,9 +2929,11 @@ void PTextEdit::musrFT()
     proc->start(cmd, fMusrFTPrevCmd);
     if (!proc->waitForStarted()) {
       // error handling
-      QString msg(tr("Could not execute the output command: ")+cmd[0]);
+      QString msg(tr("Could not execute the output command: ")+cmd+"\n"+proc->errorString());
       QMessageBox::critical( nullptr, tr("FATAL ERROR"), msg, QMessageBox::Close );
-      return;
+      proc->deleteLater();
+    } else {
+      connect(proc, SIGNAL(finished(int,QProcess::ExitStatus)), proc, SLOT(deleteLater()));
     }
   }