Reformatting Code in a Legacy Language Service
Applies to: 
Visual Studio 
Visual Studio for Mac
Note
This article applies to Visual Studio 2017. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here
In Visual Studio source code can be reformatted by normalizing the use of indentations and whitespace. This can include inserting or removing spaces or tabs at the beginning of each line, adding new lines between lines, or replacing spaces with tabs or tabs with spaces.
Note
Inserting or deleting newline characters can affect markers such as breakpoints and bookmarks, but adding or removing spaces or tabs does not affect markers.
Users can start a reformatting operation by selecting Format Selection or Format Document from the Advanced menu on the Edit menu. A reformatting operation can also be triggered when a code snippet or a particular character is inserted. For example, when you type a closing brace in C#, everything between the matching open brace and the close brace is automatically indented to the proper level.
When Visual Studio sends the Format Selection or Format Document command to the language service, the ViewFilter class calls the ReformatSpan method in the Source class. To support formatting you must override the ReformatSpan method and supply your own formatting code.
Enabling Support for Reformatting
To support formatting, the EnableFormatSelection parameter of the ProvideLanguageServiceAttribute must be set to true when you register your VSPackage. This sets the EnableFormatSelection property to true. The CanReformat method returns the value of this property. If it returns true, the ViewFilter class calls the ReformatSpan.
Implementing Reformatting
To implement reformatting, you must derive a class from the Source class and override the ReformatSpan method. The TextSpan object describes the span to format and the EditArray object holds the edits made on the span. Note that this span can be the entire document. However, since there are likely to be multiple changes made to the span, all the changes should be reversible in a single action. To do this, wrap all changes in a CompoundAction object (see "Using the CompoundAction Class" section in this topic).
Example
The following example ensures there is a single space after every comma in the selection, unless the comma is followed by a tab or is at the end of the line. Trailing spaces after the last comma in a line are deleted. See the "Using the CompoundAction Class" section in this topic to see how this method is called from the ReformatSpan method.
using Microsoft.VisualStudio.Package;
using Microsoft VisualStudio.TextManager.Interop;
namespace MyLanguagePackage
{
class MySource : Source
{
private void DoFormatting(EditArray mgr, TextSpan span)
{
// Make sure there is one space after every comma unless followed
// by a tab or comma is at end of line.
IVsTextLines pBuffer = GetTextLines();
if (pBuffer != null)
{
int startIndex = span.iStartIndex;
int endIndex = 0;
string line = "";
// Loop over all lines in span
for (int i = span.iStartLine; i <= span.iEndLine; i++)
{
if (i < span.iEndLine)
{
pBuffer.GetLengthOfLine(i, out endIndex);
}
else
{
endIndex = span.iEndIndex;
}
pBuffer.GetLineText(i, startIndex, i, endIndex, out line);
if (line.Length > 0)
{
int index = 0;
// Loop over all commas in line
while ((index = line.IndexOf(',', index)) != -1)
{
int spaceIndex = index + 1;
// Determine how many spaces after comma
while (spaceIndex < line.Length && line[spaceIndex] == ' ')
{
++spaceIndex;
}
int spaceCount = spaceIndex - (index + 1);
string replacementText = " ";
bool fDoEdit = true;
TextSpan editTextSpan = new TextSpan();
editTextSpan.iStartLine = i;
editTextSpan.iEndLine = i;
editTextSpan.iStartIndex = index + 1;
if (spaceIndex == line.Length)
{
if (spaceCount > 0)
{
// Delete spaces after a comma at end of line
editTextSpan.iEndIndex = spaceIndex;
replacementText = "";
}
else
{
// Otherwise, do not add spaces if comma is
// at end of line.
fDoEdit = false;
}
}
else if (spaceCount == 0)
{
if (spaceIndex < line.Length && line[spaceIndex] == '\t')
{
// Do not insert space if a tab follows
// a comma.
fDoEdit = false;
}
else
{
// No space after comma so add a space.
editTextSpan.iEndIndex = index + 1;
}
}
else if (spaceCount > 1)
{
// More than one space after comma, replace
// with a single space.
editTextSpan.iEndIndex = spaceIndex;
}
else
{
// Single space after a comma and not at end
// of the line, leave it alone.
fDoEdit = false;
}
if (fDoEdit)
{
// Add edit operation
mgr.Add(new EditSpan(editTextSpan, replacementText));
}
index = spaceIndex;
}
}
startIndex = 0; // All subsequent lines start at 0
}
// Apply all edits
mgr.ApplyEdits();
}
}
}
}
Using the CompoundAction Class
All the reformatting done on a section of code should be reversible in a single action. This can be accomplished using a CompoundAction class. This class wraps a set of edit operations on the text buffer into a single edit operation.
Example
Here is an example of how to use the CompoundAction class. See the example in the "Implementing Support for Formatting" section in this topic for an example of the DoFormatting method.
using Microsoft.VisualStudio.Package;
using Microsoft VisualStudio.TextManager.Interop;
namespace MyLanguagePackage
{
class MySource : Source
{
public override void ReformatSpan(EditArray mgr, TextSpan span)
{
string description = "Reformat code";
CompoundAction ca = new CompoundAction(this, description);
using (ca)
{
ca.FlushEditActions(); // Flush any pending edits
DoFormatting(mgr, span); // Format the span
}
}
}
}