BlockFile.cpp does not depend on MissingAliasFileDialog.cpp ...

... instead use a hook function to call back when it is discovered that a
block file is missing.

This frees three files from dependency cycles

src/BlockFile.cpp

@@ -53,7 +53,6 @@ out.
 #include "sndfile.h"
 #include "FileException.h"
 #include "FileFormats.h"
-#include "MissingAliasFileDialog.h"
 
 // msmeyer: Define this to add debug output via wxPrintf()
 //#define DEBUG_BLOCKFILE
@@ -479,6 +478,23 @@ bool BlockFile::Read64K(float *buffer,
    return result;
 }
 
+namespace {
+   BlockFile::MissingAliasFileFoundHook &GetMissingAliasFileFound()
+   {
+      static BlockFile::MissingAliasFileFoundHook theHook;
+      return theHook;
+   }
+}
+
+auto BlockFile::SetMissingAliasFileFound( MissingAliasFileFoundHook hook )
+   -> MissingAliasFileFoundHook
+{
+   auto &theHook = GetMissingAliasFileFound();
+   auto result = theHook;
+   theHook = hook;
+   return result;
+}
+
 size_t BlockFile::CommonReadData(
    bool mayThrow,
    const wxFileName &fileName, bool &mSilentLog,
@@ -537,8 +553,9 @@ size_t BlockFile::CommonReadData(
 
          if (pAliasFile) {
             // Set a marker to display an error message for the silence
-            if (!MissingAliasFilesDialog::ShouldShow())
-               MissingAliasFilesDialog::Mark(pAliasFile);
+            auto hook = GetMissingAliasFileFound();
+            if (hook)
+               hook( pAliasFile );
          }
       }
    }

src/BlockFile.h

@@ -18,6 +18,8 @@
 
 #include "ondemand/ODTaskThread.h"
 
+#include <functional>
+
 class XMLWriter;
 
 class SummaryInfo {
@@ -49,6 +51,14 @@ inline std::shared_ptr< Result > make_blockfile (Args && ... args)
 class PROFILE_DLL_API BlockFile /* not final, abstract */ {
  public:
 
+   // Type of function to be called when opening of an alias block file for read
+   // discovers that the other audio file it depends on is absent
+   using MissingAliasFileFoundHook =
+      std::function< void(const AliasBlockFile*) >;
+   // Install a hook, and return the previous hook
+   static MissingAliasFileFoundHook
+      SetMissingAliasFileFound( MissingAliasFileFoundHook hook );
+
    // Constructor / Destructor
 
    /// Construct a BlockFile.

src/MissingAliasFileDialog.cpp

@@ -131,3 +131,12 @@ namespace MissingAliasFilesDialog {
    }
    
 }
+
+// Arrange callback from low levels of block file I/O to detect missing files
+static struct InstallHook{ InstallHook() {
+   auto hook = [](const AliasBlockFile *pAliasFile){
+      if (!MissingAliasFilesDialog::ShouldShow())
+         MissingAliasFilesDialog::Mark(pAliasFile);
+   };
+   BlockFile::SetMissingAliasFileFound( hook );
+} } installHook;