and implement them for dwim-print (a.k.a. `p`) as an example.

The next step will be to expose them as structured data in
SBCommandReturnObject.

This patch is a reworking of Pete Lawrence's (@PortalPete) proposal
for better expression evaluator error messages:
https://github.com/llvm/llvm-project/pull/80938

Before:

```
$ lldb -o "expr a+b"
(lldb) expr a+b
error: <user expression 0>:1:1: use of undeclared identifier 'a'
a+b
^
error: <user expression 0>:1:3: use of undeclared identifier 'b'
a+b
  ^
```

After:

```
(lldb) expr a+b
            ^ ^
            │ ╰─ error: use of undeclared identifier 'b'
            ╰─ error: use of undeclared identifier 'a'
```

This eliminates the confusing `<user expression 0>:1:3` source
location and avoids echoing the expression to the console again, which
results in a cleaner presentation that makes it easier to grasp what's
going on. You can't see it here, bug the word "error" is now also in
color, if so desired.

Depends on https://github.com/llvm/llvm-project/pull/106442.

This reverts commit 49372d1cccf50f404d52d40ae4b663db5604eb2c.

This patch is a reworking of Pete Lawrence's (@PortalPete) proposal
for better expression evaluator error messages:
https://github.com/llvm/llvm-project/pull/80938

Before:

```
$ lldb -o "expr a+b"
(lldb) expr a+b
error: <user expression 0>:1:1: use of undeclared identifier 'a'
a+b
^
error: <user expression 0>:1:3: use of undeclared identifier 'b'
a+b
  ^
```

After:

```
(lldb) expr a+b
            ^ ^
            │ ╰─ error: use of undeclared identifier 'b'
            ╰─ error: use of undeclared identifier 'a'
```

This eliminates the confusing `<user expression 0>:1:3` source
location and avoids echoing the expression to the console again, which
results in a cleaner presentation that makes it easier to grasp what's
going on. You can't see it here, bug the word "error" is now also in
color, if so desired.

Depends on https://github.com/llvm/llvm-project/pull/106442.

…NFC]

This patch is the first patch in a series reworking of Pete Lawrence's
(@PortalPete) amazing proposal for better expression evaluator error
messages (https://github.com/llvm/llvm-project/pull/80938)

This patch is preparatory patch for improving the rendering of
expression evaluator diagnostics. Currently diagnostics are rendered
into a string and the command interpreter layer then textually parses
words like "error:" to (sometimes) color the output accordingly. In
order to enable user interfaces to do better with diagnostics, we need
to store them in a machine-readable fromat. This patch does this by
adding a new llvm::Error kind wrapping a DiagnosticDetail struct that
is used when the error type is eErrorTypeExpression. Multiple
diagnostics are modeled using llvm::ErrorList.

Right now the extra information is not used by the CommandInterpreter,
this will be added in a follow-up patch!

We have 3 different enums all expressing severity (info, warning,
error). Remove all uses with a new Severity enum in lldb-enumerations.h.

For example, the following message has the severity string "error: "
twice.
	> "error: <EXPR>:3:1: error: cannot find 'bogus' in scope

This method already appends the severity string in the beginning, but
with this fix, it also removes a secondary instance, if applicable.

Note that this change only removes the *first* redundant substring. I
considered putting the removal logic in a loop, but I decided that if
something is generating more than one redundant severity substring, then
that's a problem the message's source should probably fix.

rdar://114203423

This is how it should've been and brings it more in line with
std::string_view. There should be no functional change here.

This is mostly mechanical from a custom clang-tidy check, with a lot of
manual fixups. It uncovers a lot of minor inefficiencies.

This doesn't actually modify StringRef yet, I'll do that in a follow-up.

Summary:
A *.cpp file header in LLDB (and in LLDB) should like this:
```
//===-- TestUtilities.cpp -------------------------------------------------===//
```
However in LLDB most of our source files have arbitrary changes to this format and
these changes are spreading through LLDB as folks usually just use the existing
source files as templates for their new files (most notably the unnecessary
editor language indicator `-*- C++ -*-` is spreading and in every review
someone is pointing out that this is wrong, resulting in people pointing out that this
is done in the same way in other files).

This patch removes most of these inconsistencies including the editor language indicators,
all the different missing/additional '-' characters, files that center the file name, missing
trailing `===//` (mostly caused by clang-format breaking the line).

Reviewers: aprantl, espindola, jfb, shafik, JDevlieghere

Reviewed By: JDevlieghere

Subscribers: dexonsmith, wuzish, emaste, sdardis, nemanjai, kbarton, MaskRay, atanasyan, arphaman, jfb, abidh, jsji, JDevlieghere, usaxena95, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D73258