[PATCH] D58784: [FileCheck]Remove assertions that prevent matching an empty string at file start before CHECK-NEXT/SAME

[Joel E. Denny via Phabricator via llvm-commits]

jdenny added a comment.

In D58784#1414493 <https://reviews.llvm.org/D58784#1414493>, @probinson wrote:

> > The following appears to be equivalent to what an initial CHECK-EMPTY should do:
> > 
> >   CHECK: {{^}}
> >   CHECK-SAME: {{^$}}
>
> Yep.  So if we allow an initial CHECK-SAME, defining the search range as starting at the beginning of the input, then an initial `CHECK-SAME: stuff` verifies that `stuff` appears on the first line, and `CHECK-SAME: {{^$}}` verifies the first line is empty.  That seems pretty intuitive to me.


I see what you mean, but see below.

> Am I reading the docs rightly, it looks like `CHECK-EMPTY` is exactly `CHECK-NEXT: {{^$}}` isn't it?  Did we have some other rationale for adding EMPTY, which now escapes me?

They're not the same.  If the previous match occurs at the end of the line, your CHECK-NEXT will match at the end of that line and then complain it's not on the next line.  CHECK-EMPTY skips a newline before looking for an empty line.

>> Also, an initial CHECK-SAME has no clear meaning to me.)
> 
> See above.

Here's how I see it, but I realize it's subjective.  If we say that an initial CHECK-SAME matches the first line, then, to be consistent with the relationship CHECK-SAME and CHECK-NEXT have everywhere else, an initial CHECK-NEXT should skip a new line and thus match the second line.  That means that, in order to match consecutive lines starting with the first line, we have:

  CHECK-SAME: first line
  CHECK-NEXT: second line
  CHECK-NEXT: third line

But the following seems more intuitive to me:

  CHECK-NEXT: first line
  CHECK-NEXT: second line
  CHECK-NEXT: third line

To say it more abstractly:

- CHECK-NEXT means match on the next line after the previous match.
- CHECK-SAME means match on the same line as the previous match.

If there is no previous match because this is the first directive, then that translates to:

- CHECK-NEXT means match on the next line after no match yet, and that intuitively sounds like the first line to me.
- CHECK-SAME means match on the same line as no match yet, but that sounds impossible to me.


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D58784/new/

https://reviews.llvm.org/D58784