This converts all remaining "## Sample code" segments into snippets, and fixes
the snippet generator to handle multiple snippets in the same dartdoc block
properly.
I also generated, compiled, and ran each of the existing application samples,
and fixed them up to be more useful and/or just run without errors.
This PR fixes these problems with examples:
1. Switching tabs in a snippet now works if there is more than one snippet in
a single dartdoc block.
2. Generation of snippet code now works if there is more than one snippet.
3. Contrast of text and links in the code sample block has been improved to
recommended levels.
4. Added five new snippet templates, including a "freeform" template to make
it possible to show examples that need to change the app instantiation.
5. Fixed several examples to run properly, a couple by adding the "Scaffold"
widget to the template, a couple by just fixing their code.
6. Fixed visual look of some of the samples when they run by placing many
samples inside of a Scaffold.
7. In order to make it easier to run locally, changed the sample analyzer to
remove the contents of the supplied temp directory before running, since
having files that hang around is problematic (only a problem when running
locally with the `--temp` argument).
8. Added a `SampleCheckerException` class, and handle sample checking
exceptions more gracefully.
9. Deprecated the old "## Sample code" designation, and added enforcement for
the deprecation.
10. Removed unnecessary `new` from templates (although they never appeared in
the samples thanks to dartfmt, but still).
Fixes#26398Fixes#27411
This converts existing ## Sample code samples to {@tool sample}...{@end-tool} form.
Also:
1. Fixed a minor bug in analyze-sample-code.dart
2. Made the snippet tool only insert descriptions if the description is non-empty.
3. Moved the Card diagram to before the code sample.
This rewrites the sample code analysis script to be a little less of a hack (but still not pretty), and to handle snippets as well.
It also changes the semantics of how sample code is handled: the namespace for the sample code is now limited to the file that it appears in, so some additional "Examples can assume:" blocks were added. The upside of this is that there will be far fewer name collisions.
I fixed the output too: no longer will you get 4000 lines of numbered output with the error at the top and have to grep for the actual problem. It gives the filename and line number of the original location of the code (in the comment in the tree), and prints out the source code on the line that caused the problem along with the error.
For snippets, it prints out the location of the start of the snippet and the source code line that causes the problem. It can't print out the original line, because snippets get formatted when they are written, so the line might not be in the same place.
