This is an implementation for [bug 17362](https://bugs.llvm.org/attachment.cgi?bugid=17362) which adds support for indenting preprocessor statements inside if/ifdef/endif. This takes previous work from fmauch (https://github.com/fmauch/clang/tree/preprocessor_indent) and makes it into a full feature.
The context of this patch is that I'm a VMware intern, and I implemented this because VMware needs the feature. As such, some decisions were made based on what VMware wants, and I would appreciate suggestions on expanding this if necessary to use-cases other people may want.
This adds a new enum config option, `IndentPPDirectives`. Values are:
* `PPDIS_None` (in config: `None`):
* `PPDIS_AfterHash` (in config: `AfterHash`):
# if BAR
# include <foo>
This is meant to work whether spaces or tabs are used for indentation.
Preprocessor indentation also attempts to ignore include guards with the checks:
1. Include guards cover the entire file
2. Include guards don't have `#else`
3. Include guards begin with
This patch allows `UnwrappedLineParser::PPBranchLevel` to be decremented to -1 (the initial value is -1) so the variable can be used for indent tracking.
* This patch does not handle the case where there's code between the `#ifndef` and `#define` but all other conditions hold. This is because when the #define line is parsed, `UnwrappedLineParser::Lines` doesn't hold the previous code line yet, so we can't detect it. This is out of the scope of this patch.
* This patch does not handle cases where legitimate lines may be outside an include guard. Examples are `#pragma once` and `#pragma GCC diagnostic`, or anything else that does not change the meaning of the file if it's included multiple times.
* This does not detect when there is a single non-preprocessor line in front of an include-guard-like structure where other conditions hold because `ScopedLineState` hides the line.