[SYCL][COMPAT] Fix error on headers, add helloworld test

[Ruyk]

This PR fixes an error on the SYCL compat headers that caused build to fail.
The error manifests when building the basic hello world from the documentation.
To prevent the basic hello world from failing again, this PR adds an e2e for the basic hello world
and updates the documentation to match the updated hello world source code.

[Copilot]

Pull Request Overview

This PR fixes a build error in the SYCL compat headers and adds an end-to-end test for the basic hello world example while updating the corresponding documentation.

• Fixes header issues causing build failures in SYCLcompat.
• Adds an e2e test (helloworld.cpp) to verify the hello world example.
• Updates the documentation to reflect the changes in header includes and error checking.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
sycl/test-e2e/Compat/helloworld.cpp	Adds an e2e test for the hello world example
sycl/include/syclcompat/traits.hpp	Updates type alias to use correct item instantiation
sycl/doc/syclcompat/README.md	Updates header include path and error checking logic

[ldrumm]

I don't like this direction. It's just going to diverge very shortly. If you want tests to test examples in documentation, then the correct way to do this is with a tool that parses the documentation and then builds that code, or conversely preprocesses a documentation template to include an external source file.
As it stands this doesn't test the documentation. It tests another piece of code somewhere else in the repository.

Worse: There's no note in the actual test file to say that it needs to be kept in sync with the README so we're pretty much guaranteed divergence unless someone's very careful with the git log...
Which brings up the second point: this PR does not do what the description says. It's described as fixing a header error, but it's actually about testing example code in documentation

Please reconsider this patch.

[ldrumm]

The correct way to do this is with a tool that parses the documentation and then builds that code

#!/usr/bin/env python

import sys
import tempfile
import re
import subprocess

ASCIIDOC_HEADER_PATTERN = re.compile(
    r'^==+ example (?P<example_name>[0-9]+)\s*$',
    re.IGNORECASE | re.UNICODE
)


def parse_example_sections(lines):
    sections = {}

    i = -1
    while i < len(lines) - 1:
        i += 1
        if not (match := ASCIIDOC_HEADER_PATTERN.match(lines[i])):
            continue
        if lines[i + 1].strip() != '[source,c++]':
            continue
        if lines[i + 2].strip() != '----':
            continue
        start = i + 3
        i = start
        while i < len(lines) and lines[i].strip() != '----':
            i += 1
        end = i
        sections[match.groupdict()['example_name']] = lines[start:end]
    return sections


if __name__ == '__main__':
    import argparse
    parser = argparse.ArgumentParser()
    parser.add_argument(
        'infile', nargs='?',
        type=argparse.FileType('r'),
        default=sys.stdin

    )
    known_args, extra_args = parser.parse_known_args()
    examples = parse_example_sections(known_args.infile.readlines())

    for example, source in examples.items():
        source = ''.join(source)
        print(f"compiling example {example}:")
        print(source)
        print("-------------------------------------------")
        with tempfile.NamedTemporaryFile(suffix='.cpp', delete=False) as f:
            f.write(source.encode('utf-8'))
            f.flush()
            subprocess.check_call(['clang++', '-fsycl',
            '-fsycl-targets=amdgcn-amd-amdhsa',
            '-Xsycl-target-backend=amdgcn-amd-amdhsa', '--offload-arch=gfx1032',
            '--rocm-path=/home/luke/h/hip/install'] + extra_args + [f.name])
        subprocess.check_call(['./a.out'])
        print(f"{example} passed")

Here's one I wrote for local testing of example code in a sycl extension doc I worked on. Should be simple to adapt the idea to markdown

[Ruyk]

The correct way to do this is with a tool that parses the documentation and then builds that code

#!/usr/bin/env python

import sys
import tempfile
import re
import subprocess

ASCIIDOC_HEADER_PATTERN = re.compile(
    r'^==+ example (?P<example_name>[0-9]+)\s*$',
    re.IGNORECASE | re.UNICODE
)


def parse_example_sections(lines):
    sections = {}

    i = -1
    while i < len(lines) - 1:
        i += 1
        if not (match := ASCIIDOC_HEADER_PATTERN.match(lines[i])):
            continue
        if lines[i + 1].strip() != '[source,c++]':
            continue
        if lines[i + 2].strip() != '----':
            continue
        start = i + 3
        i = start
        while i < len(lines) and lines[i].strip() != '----':
            i += 1
        end = i
        sections[match.groupdict()['example_name']] = lines[start:end]
    return sections


if __name__ == '__main__':
    import argparse
    parser = argparse.ArgumentParser()
    parser.add_argument(
        'infile', nargs='?',
        type=argparse.FileType('r'),
        default=sys.stdin

    )
    known_args, extra_args = parser.parse_known_args()
    examples = parse_example_sections(known_args.infile.readlines())

    for example, source in examples.items():
        source = ''.join(source)
        print(f"compiling example {example}:")
        print(source)
        print("-------------------------------------------")
        with tempfile.NamedTemporaryFile(suffix='.cpp', delete=False) as f:
            f.write(source.encode('utf-8'))
            f.flush()
            subprocess.check_call(['clang++', '-fsycl',
            '-fsycl-targets=amdgcn-amd-amdhsa',
            '-Xsycl-target-backend=amdgcn-amd-amdhsa', '--offload-arch=gfx1032',
            '--rocm-path=/home/luke/h/hip/install'] + extra_args + [f.name])
        subprocess.check_call(['./a.out'])
        print(f"{example} passed")

Here's one I wrote for local testing of example code in a sycl extension doc I worked on. Should be simple to adapt the idea to markdown

Thanks for the script. For this particular PR, I am just going to remove the actual sample code from the README and change it as a link to the test.
The README file itself needs to be redone to rely less on code snippets and be more practical, which I'll do in a separate PR.

[Ruyk]

@ldrumm , just to clarify, the patch fixes the error, see the traits.hpp file. It also adds a test to make sure the error does not get re-introduced. I could split the two things in two patches, but I rather have the bug and the test to prevent it together.