[gnome-text-editor] document: guess content-type after typing first line

[Christian Hergert <chergert src gnome org>]

commit 18ffdf35dbe5296041af3dfcf0f651e97c401592
Author: Christian Hergert <chergert redhat com>
Date:   Wed Jun 30 12:34:47 2021 -0700

    document: guess content-type after typing first line
    
    This is similar to what we do in Builder so that we can guess content
    type after the user types the first line. Emacs also does something
    similar.
    
    For common scripting cases, this just works. Put a shebang on the first
    line, and it will get picked up. Same for includes on C sources.
    
    Related #24

 src/editor-document.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)
---
diff --git a/src/editor-document.c b/src/editor-document.c
index 3004998..d825255 100644
--- a/src/editor-document.c
+++ b/src/editor-document.c
@@ -188,6 +188,40 @@ editor_document_changed (GtkTextBuffer *buffer)
   editor_document_apply_spacing (self);
 }
 
+static void
+editor_document_guess_content_type (EditorDocument *self)
+{
+  GtkSourceLanguageManager *manager;
+  GtkSourceLanguage *language;
+  g_autofree char *content = NULL;
+  g_autofree char *content_type = NULL;
+  g_autofree char *filename = NULL;
+  GtkTextIter begin, end;
+  GFile *file;
+  gboolean uncertain;
+
+  g_assert (EDITOR_IS_DOCUMENT (self));
+
+  /* Ignore if we already have a language */
+  if ((language = gtk_source_buffer_get_language (GTK_SOURCE_BUFFER (self))))
+    return;
+
+  /* Read the first page of data and use it to guess content-type */
+  gtk_text_buffer_get_start_iter (GTK_TEXT_BUFFER (self), &begin);
+  gtk_text_buffer_get_iter_at_offset (GTK_TEXT_BUFFER (self), &end, 4095);
+  content = gtk_text_iter_get_slice (&begin, &end);
+
+  if ((file = editor_document_get_file (self)))
+    filename = g_file_get_basename (file);
+
+  content_type = g_content_type_guess (filename, (const guchar *)content, strlen (content), &uncertain);
+  manager = gtk_source_language_manager_get_default ();
+  language = gtk_source_language_manager_guess_language (manager, filename, content_type);
+
+  if (language)
+    gtk_source_buffer_set_language (GTK_SOURCE_BUFFER (self), language);
+}
+
 static void
 editor_document_insert_text (GtkTextBuffer *buffer,
                              GtkTextIter   *pos,
@@ -195,6 +229,7 @@ editor_document_insert_text (GtkTextBuffer *buffer,
                              gint           new_text_length)
 {
   EditorDocument *self = (EditorDocument *)buffer;
+  guint line;
   guint offset;
   guint length;
 
@@ -202,6 +237,7 @@ editor_document_insert_text (GtkTextBuffer *buffer,
   g_assert (pos != NULL);
   g_assert (new_text != NULL);
 
+  line = gtk_text_iter_get_line (pos);
   offset = gtk_text_iter_get_offset (pos);
 
   GTK_TEXT_BUFFER_CLASS (editor_document_parent_class)->insert_text (buffer, pos, new_text, new_text_length);
@@ -213,6 +249,9 @@ editor_document_insert_text (GtkTextBuffer *buffer,
 
   if (offset < TITLE_MAX_LEN && editor_document_get_file (self) == NULL)
     g_object_notify_by_pspec (G_OBJECT (self), properties [PROP_TITLE]);
+
+  if (self->busy_count == 0 && line == 0 && strchr (new_text, '\n'))
+    editor_document_guess_content_type (self);
 }
 
 static void