[FileCheck] Annotate input dump (6/7)

This patch implements input annotations for diagnostics reporting
CHECK-DAG discarded matches.  These diagnostics are enabled by -vv.
These annotations mark discarded match ranges using `!~~` because they
are bad matches even though they are not errors.

CHECK-DAG discarded matches create another case where there can be
multiple match results for the same directive.

For example:

```
$ FileCheck -dump-input=help
The following description was requested by -dump-input=help to
explain the input annotations printed by -dump-input=always and
-dump-input=fail:

  - L:     labels line number L of the input file
  - T:L    labels the only match result for a pattern of type T from line L of
           the check file
  - T:L'N  labels the Nth match result for a pattern of type T from line L of
           the check file
  - ^~~    marks good match (reported if -v)
  - !~~    marks bad match, such as:
           - CHECK-NEXT on same line as previous match (error)
           - CHECK-NOT found (error)
           - CHECK-DAG overlapping match (discarded, reported if -vv)
  - X~~    marks search range when no match is found, such as:
           - CHECK-NEXT not found (error)
           - CHECK-DAG not found after discarded matches (error)
  - ?      marks fuzzy match when no match is found
  - colors success, error, fuzzy match, discarded match, unmatched input

If you are not seeing color above or in input dumps, try: -color

$ FileCheck -vv -dump-input=always check4 < input4 |& sed -n '/^<<<</,$p'
<<<<<<
         1: abcdef
dag:1       ^~~~
dag:2'0       !~~~ discard: overlaps earlier match
         2: cdefgh
dag:2'1     ^~~~
check:3         X~ error: no match found
>>>>>>

$ cat check4
CHECK-DAG: abcd
CHECK-DAG: cdef
CHECK: efgh

$ cat input4
abcdef
cdefgh
```

This shows that the line 3 CHECK fails to match even though its
pattern appears in the input because its search range starts after the
line 2 CHECK-DAG's match range.  The trouble might be that the line 2
CHECK-DAG's match range is later than expected because its first match
range overlaps with the line 1 CHECK-DAG match range and thus is
discarded.

Because `!~~` for CHECK-DAG does not indicate an error, it is not
colored red.  Instead, when colors are enabled, it is colored cyan,
which suggests a match that went cold.

Reviewed By: george.karpenkov, probinson

Differential Revision: https://reviews.llvm.org/D53898

llvm-svn: 349423

0 files changed, 0 insertions, 0 deletions