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[clang-format] Fix AlignConsecutive on PP blocks

Authored by MyDeveloperDay on May 13 2020, 10:27 AM.

Description

[clang-format] Fix AlignConsecutive on PP blocks

Summary:
Currently the 'AlignConsecutive*' options incorrectly align across
elif and else statements, even if they are very far away and across
unrelated preprocessor macros.

This failed since on preprocessor run 2+, there is not enough context
about the #ifdefs to actually differentiate one block from another,
causing them to align across different blocks or even large sections of
the file.

Eg, with AlignConsecutiveAssignments:

\#if FOO      // Run 1
\#else        // Run 1
int a   = 1;  // Run 2, wrong
\#endif       // Run 1

\#if FOO      // Run 1
\#else        // Run 1
int bar = 1;  // Run 2
\#endif       // Run 1

is read as

int a   = 1;  // Run 2, wrong
int bar = 1;  // Run 2

The approach taken to fix this was to add a new flag to Token that
forces breaking alignment across groups of lines (MustBreakAlignBefore)
in a similar manner to the existing flag that forces a line break
(MustBreakBefore). This flag is set for the first Token after a
preprocessor statement or diff conflict marker.

Fixes #25167,#31281

Patch By: JakeMerdichAMD

Reviewed By: MyDeveloperDay

Tags: #clang, #clang-format

Differential Revision: https://reviews.llvm.org/D79388