Is there a way in Sketch to expand a shape? For example, let's say I have an outline of something. I'd like to expand that outline to be a solid shape so I can apply boolean operations to it with other shapes. Is that possible?
The accepted answer seems to be deprecated as of Sketch 3.6.1
Layer > Paths > Vectorize Stroke is gone, instead now we got Layer > Convert to Outlines
EDIT for Sketch 3.6.1
Choose Layer > Convert to Outlines.
Strokes cannot be expanded (currently, v2.4.3). Edit: You can choose vectorize stroke in Layer (or Edit for older version) > Paths > Vectorize Stroke
However, you could create the shape and then use a mask to make the diagonal cut. In the example I have made the mask visible in red (normally this would not be shown).
You can create a mask by drawing a single shape (can be constructed using boolean shapes). Then select 'Use as Mask' when ctrl-clicking the layer in the layer pane. Make sure you position the layer right below the layer you want to mask (in the layer pane).
Choose the border you want to convert into the shape and go to Layer > Convert to outline