Qt: Add dfilter error location to tooltip

If display filter compilation fails and the expression has a syntax
error and associated location, it will be displayed in the filter
tooltip, using a textual underline.

As far as I can tell using a graphical squiggly underline seems extremely
difficult for an object inheriting from QLineEdit, so the tooltip
textual method was used instead.

ui/qt/widgets/display_filter_edit.cpp

@@ -357,9 +357,8 @@ void DisplayFilterEdit::checkFilter(const QString& filter_text)
     }
     case Invalid:
     {
-        QString invalidMsg = tr("Invalid filter: ").append(syntaxErrorMessage());
         mainApp->pushStatus(MainApplication::FilterSyntax, syntaxErrorMessage());
-        setToolTip(invalidMsg);
+        setToolTip(syntaxErrorMessageFull());
         break;
     }
     default:

ui/qt/widgets/syntax_line_edit.cpp

@@ -135,10 +135,33 @@ void SyntaxLineEdit::setSyntaxState(SyntaxState state) {
     setStyleSheet(style_sheet_);
 }
 
-QString SyntaxLineEdit::syntaxErrorMessage() {
+QString SyntaxLineEdit::syntaxErrorMessage()
+{
     return syntax_error_message_;
 }
 
+QString SyntaxLineEdit::syntaxErrorMessageFull()
+{
+    return syntax_error_message_full_;
+}
+
+QString SyntaxLineEdit::createSyntaxErrorMessageFull(
+                                const QString &filter, const QString &err_msg,
+                                qsizetype loc_start, size_t loc_length)
+{
+    QString msg = tr("Invalid filter: %1").arg(err_msg);
+
+    if (loc_start >= 0 && loc_length >= 1) {
+        // Add underlined location
+        msg = QString("<p>%1<pre>  %2\n  %3^%4</pre></p>")
+            .arg(msg)
+            .arg(filter)
+            .arg(QString(' ').repeated(loc_start))
+            .arg(QString('~').repeated(loc_length - 1));
+    }
+    return msg;
+}
+
 QString SyntaxLineEdit::styleSheet() const {
     return style_sheet_;
 }
@@ -179,7 +202,8 @@ bool SyntaxLineEdit::checkDisplayFilter(QString filter)
 
     dfilter_t *dfp = NULL;
     gchar *err_msg;
-    if (dfilter_compile(filter.toUtf8().constData(), &dfp, &err_msg)) {
+    dfilter_loc_t loc;
+    if (dfilter_compile2(filter.toUtf8().constData(), &dfp, &err_msg, &loc)) {
         GPtrArray *depr = NULL;
         if (dfp) {
             depr = dfilter_deprecated_tokens(dfp);
@@ -208,6 +232,7 @@ bool SyntaxLineEdit::checkDisplayFilter(QString filter)
     } else {
         setSyntaxState(SyntaxLineEdit::Invalid);
         syntax_error_message_ = QString::fromUtf8(err_msg);
+        syntax_error_message_full_ = createSyntaxErrorMessageFull(filter, syntax_error_message_, loc.col_start, loc.col_len);
         g_free(err_msg);
     }
     dfilter_free(dfp);

ui/qt/widgets/syntax_line_edit.h

@@ -31,13 +31,19 @@ class SyntaxLineEdit : public QLineEdit
     SyntaxState syntaxState() const { return syntax_state_; }
     void setSyntaxState(SyntaxState state = Empty);
     QString syntaxErrorMessage();
+    // Error message with filter expression and location error.
+    QString syntaxErrorMessageFull();
     QString styleSheet() const;
     QString deprecatedToken();
 
     void setCompleter(QCompleter *c);
     QCompleter *completer() const { return completer_; }
     void allowCompletion(bool enabled);
 
+    static QString createSyntaxErrorMessageFull(const QString &filter,
+                                                const QString &err_msg,
+                                                qsizetype loc_start, size_t loc_length);
+
 public slots:
     void setStyleSheet(const QString &style_sheet);
     // Insert filter text at the current position, adding spaces where needed.
@@ -69,6 +75,7 @@ public slots:
     QString style_sheet_;
     QString state_style_sheet_;
     QString syntax_error_message_;
+    QString syntax_error_message_full_;
     QString token_chars_;
     bool completion_enabled_;