Tests where the RUN-lines/CHECK-ed output refer to line numbers in the test
file are a maintenance burden, as inserting text in the appropriate place
invalidates all the subsequent line numbers.

Lit supports %(line+n) for this, and FileCheck supports [[@LINE+N]].
But many existing tests don't make use of it and still need to be modified.

This commit adds a script that can find line numbers in tests according to a
regex and replace them with the appropriate relative-line reference.
It contains some options to avoid inappropriately rewriting tests where absolute
numbers are appropriate: a "nearby" threshold and a refusal by default to
replace only some matched line numbers.

I've applied it to CodeComplete tests, this proves the concept but also are the
single worst group of tests I've seen in this respect.
These changes are likely to hit merge conflicts, but can be regenerated with:

```
find ../clang/test/CodeCompletion/ -type f | grep -v /Inputs/ | xargs ../llvm/utils/relative_lines.py --verbose --near=20 --pattern='-code-completion-at[ =]%s:(\\d+):' --pattern='requires fix-it: {(\d+):\d+-(\d+):\d+}'
````

As requested in https://reviews.llvm.org/D140044

Fixes https://github.com/llvm/llvm-project/issues/59553

Differential Revision: https://reviews.llvm.org/D140217

Various tests had sprung up over the years which had --check-prefix=ABC on the
RUN line, but "CHECK-ABC:" later on. This happened to work before, but was
strictly incorrect. FileCheck is getting stricter soon though.

Patch by Ron Ofir.

llvm-svn: 188174

the "typed" text, first, then take into account
nested-name-specifiers, name hiding, etc. This means that the
resulting sort is actually alphabetical :)

llvm-svn: 93370

 - This is designed to make it obvious that %clang_cc1 is a "test variable"
   which is substituted. It is '%clang_cc1' instead of '%clang -cc1' because it
   can be useful to redefine what gets run as 'clang -cc1' (for example, to set
   a default target).

llvm-svn: 91446

llvm-svn: 86432

 - 'for i in $(find . -type f); do sed -e 's#\(RUN:.*[^ ]\) *&& *$#\1#g' $i | FileUpdate $i; done', for the curious.

llvm-svn: 86430

  -code-completion-at=filename:line:column

which performs code completion at the specified location by truncating
the file at that position and enabling code completion. This approach
makes it possible to run multiple tests from a single test file, and
gives a more natural command-line interface.

llvm-svn: 82571

"->", or "::" if we will be looking into a dependent context. It's not
wrong to use the "template" keyword, but it's to needed, either.

llvm-svn: 82307

essence, code completion is triggered by a magic "code completion"
token produced by the lexer [*], which the parser recognizes at
certain points in the grammar. The parser then calls into the Action
object with the appropriate CodeCompletionXXX action.

Sema implements the CodeCompletionXXX callbacks by performing minimal
translation, then forwarding them to a CodeCompletionConsumer
subclass, which uses the results of semantic analysis to provide
code-completion results. At present, only a single, "printing" code
completion consumer is available, for regression testing and
debugging. However, the design is meant to permit other
code-completion consumers.

This initial commit contains two code-completion actions: one for
member access, e.g., "x." or "p->", and one for
nested-name-specifiers, e.g., "std::". More code-completion actions
will follow, along with improved gathering of code-completion results
for the various contexts.

[*] In the current -code-completion-dump testing/debugging mode, the
file is truncated at the completion point and EOF is translated into
"code completion".

llvm-svn: 82166