I am trying to create a dashed line that initially has small dashes and large gaps between each dash. The dashes lengths should increase while the gaps decrease until the point is reached that the line becomes solid. Is there any way to do this other than manually drawing in the line lengths?
If all you need is a straight line, my first thought is to try to use the the blend tool on two horizontal lines, one short and one longer one. Like so:
Then fiddle with the exact segment length, stroke weight and the number of steps in the Blend Options dialog to get the effect you want. You may end up with overlapping lines and you'll have to join them and remove the extra anchor points.
And actually, I think you could apply this to a curved path, by Expanding the blend (with the entire blend object selected, go to Object --> Blend --> Expand), then drag the expanded group of lines to the Brushes panel and create a Pattern Brush.
You can do a horizontal blend for example between a short dash and a longer dash, then play with all numeric values, the length of the lines, number of steps in the blend, etc. Probably other ways to do this.
My approach was minorly labour-intensive, but nothing like as bad a "manually drawing in the line lengths" - I drew the entire path, set an initial dash + gap, then cut the curve at several points along its length - in each succeeding section, I incremented the gap down by 2 points, and the dash length up by 2 points.
Looked like this in the end: