Button for showing PDF if compilation error

Building on cd8be655, we still allow viewing a produced PDF even if
there were compilation errors. However, now the user must click the
"Show Output Anyway" button in the LaTeX Errors dialog. The reason
is that before, there was a chance that the user would not realize
there was an error (because the PDF would be shown over the error
dialog). The approach in this commit makes it more clear that there
is an error.

A new LFUN is introduced, LFUN_BUFFER_VIEW_CACHE. It is useful not
just for the implementation of the "Show Output Anyway" button, but
also to show the last compiled version of a document, which can save
time if a document takes a long time to compile (e.g. heavy use of
knitr).

src/Buffer.cpp

@@ -285,6 +285,10 @@ public:
 	/// we ran updateBuffer(), i.e., whether citation labels may need
 	/// to be updated.
 	mutable bool cite_labels_valid_;
+	/// these hold the file name and format, written to by Buffer::preview
+	/// and read from by LFUN_BUFFER_VIEW_CACHE.
+	FileName preview_file_;
+	string preview_format_;
 
 	mutable RefCache ref_cache_;
 
@@ -420,6 +424,8 @@ Buffer::Impl::Impl(Buffer * owner, FileName const & file, bool readonly_,
 	cite_labels_valid_ = cloned_buffer_->d->cite_labels_valid_;
 	unnamed = cloned_buffer_->d->unnamed;
 	internal_buffer = cloned_buffer_->d->internal_buffer;
+	preview_file_ = cloned_buffer_->d->preview_file_;
+	preview_format_ = cloned_buffer_->d->preview_format_;
 }
 
 
@@ -2420,6 +2426,10 @@ bool Buffer::getStatus(FuncRequest const & cmd, FuncStatus & flag)
 		enable = !isReadonly();
 		break;
 
+	case LFUN_BUFFER_VIEW_CACHE:
+		enable = (d->preview_file_).exists();
+		break;
+
 	default:
 		return false;
 	}
@@ -2759,6 +2769,12 @@ void Buffer::dispatch(FuncRequest const & func, DispatchResult & dr)
 		break;
 	}
 
+	case LFUN_BUFFER_VIEW_CACHE:
+		if (!formats.view(*this, d->preview_file_,
+				  d->preview_format_))
+			dr.setMessage(_("Error viewing the output file."));
+		break;
+
 	default:
 		dispatched = false;
 		break;
@@ -4212,13 +4228,18 @@ Buffer::ExportStatus Buffer::preview(string const & format, bool includeall) con
 	// (2) export with included children only
 	ExportStatus const status = doExport(format, true, false, result_file);
 	FileName const previewFile(result_file);
+
+	LATTEST (isClone());
+	d->cloned_buffer_->d->preview_file_ = previewFile;
+	d->cloned_buffer_->d->preview_format_ = format;
+
+	if (status != ExportSuccess)
+		return status;
 	if (previewFile.exists()) {
 		if (!formats.view(*this, previewFile, format))
 			return PreviewError;
-		else if (status == ExportSuccess)
-			return PreviewSuccess;
 		else
-			return status;
+			return PreviewSuccess;
 	}
 	else {
 		// Successful export but no output file?

src/FuncCode.h

@@ -459,6 +459,7 @@ enum FuncCode
 	LFUN_SPELLING_CONTINUOUSLY,     // vfr, 20130324
 	LFUN_SEPARATOR_INSERT,          // ef 20140502
 	LFUN_SERVER_GET_STATISTICS,     // brokenclock 20141010
+	LFUN_BUFFER_VIEW_CACHE,         // skostysh 20150401
 	LFUN_LASTACTION                 // end of the table
 };
 

src/LyXAction.cpp

@@ -1577,6 +1577,17 @@ void LyXAction::init()
  * \endvar
  */
 		{ LFUN_LAYOUT_RELOAD, "layout-reload", NoInternal, Layout },
+/*!
+ * \var lyx::FuncCode lyx::LFUN_BUFFER_VIEW_CACHE
+ * \li Action: Opens the file that was created from last preview of this buffer.
+ * \li Notion: This LFUN is called by the "Show Output Anyway" button in the LaTeX
+ *             Errors dialog. It can also be called by the user, which is useful
+ *             if the document takes a long time to compile, and you just
+ *             want to see the last previewed version.
+ * \li Syntax: buffer-view-cache
+ * \endvar
+ */
+		{ LFUN_BUFFER_VIEW_CACHE, "buffer-view-cache", ReadOnly, Buffer },
 /*!
  * \var lyx::FuncCode lyx::LFUN_TEXTCLASS_APPLY
  * \li Action: Sets the text class for the current buffer.

src/frontends/qt4/GuiErrorList.cpp

@@ -18,7 +18,9 @@
 #include "Buffer.h"
 #include "BufferView.h"
 #include "FuncRequest.h"
+#include "FuncStatus.h"
 #include "BufferList.h"
+#include "LyX.h"
 #include "ParIterator.h"
 #include "Text.h"
 
@@ -63,11 +65,14 @@ GuiErrorList::GuiErrorList(GuiView & lv)
 		this, SLOT(slotClose()));
 	connect(viewLogPB, SIGNAL(clicked()),
 		this, SLOT(viewLog()));
+	connect(showAnywayPB, SIGNAL(clicked()),
+		this, SLOT(showAnyway()));
 	connect(errorsLW, SIGNAL(currentRowChanged(int)),
 		this, SLOT(select()));
 
 	bc().setPolicy(ButtonPolicy::OkCancelPolicy);
 	bc().setCancel(closePB);
+	showAnywayPB->setEnabled(lyx::getStatus(FuncRequest(LFUN_BUFFER_VIEW_CACHE)).enabled());
 }
 
 
@@ -102,6 +107,12 @@ void GuiErrorList::viewLog()
 }
 
 
+void GuiErrorList::showAnyway()
+{
+	dispatch(FuncRequest(LFUN_BUFFER_VIEW_CACHE));
+}
+
+
 void GuiErrorList::paramsToDialog()
 {
 	setTitle(toqstr(name_));

src/frontends/qt4/GuiErrorList.h

@@ -33,6 +33,8 @@ public Q_SLOTS:
 	void select();
 	/// open the LaTeX log
 	void viewLog();
+	/// show the output file despite compilation errors
+	void showAnyway();
 
 private:
 	///

src/frontends/qt4/ui/ErrorListUi.ui

@@ -22,7 +22,7 @@
    <property name="spacing" >
     <number>6</number>
    </property>
-   <item row="3" column="0" colspan="3" >
+   <item row="3" column="0" colspan="4" >
     <widget class="QTextBrowser" name="descriptionTB" >
      <property name="sizePolicy" >
       <sizepolicy>
@@ -54,14 +54,14 @@
      </property>
     </widget>
    </item>
-   <item row="4" column="2" >
+   <item row="4" column="3" >
     <widget class="QPushButton" name="closePB" >
      <property name="text" >
       <string>&amp;Close</string>
      </property>
     </widget>
    </item>
-   <item row="4" column="1" >
+   <item row="4" column="2" >
     <spacer>
      <property name="orientation" >
       <enum>Qt::Horizontal</enum>
@@ -87,7 +87,18 @@
      </property>
     </widget>
    </item>
-   <item row="1" column="0" colspan="3" >
+   <item row="4" column="1" >
+    <widget class="QPushButton" name="showAnywayPB" >
+     <property name="toolTip" >
+       <string>Attempt to show the output even if there were
+compilation errors</string>
+     </property>
+     <property name="text" >
+      <string>Show Output &amp;Anyway</string>
+     </property>
+    </widget>
+   </item>
+   <item row="1" column="0" colspan="4" >
     <widget class="QListWidget" name="errorsLW" >
      <property name="toolTip" >
       <string>Selecting an error will show the error message in the panel below,