[C++] S3FileSystem::MakeUri drops bucket from path

[raulcd]

Describe the bug, including details regarding any error messages, version, and platform.

The following new ad-hoc test:

TEST_F(S3OptionsTest, MakeUri) {
  S3Options options;
  options.ConfigureAccessKey("minio", "miniopass");
  options.region = "us-east-1";
  ASSERT_OK_AND_ASSIGN(auto fs, S3FileSystem::Make(options));
  ASSERT_OK_AND_ASSIGN(auto uri, fs->MakeUri("/bucket/somedir/subdir/subfile"));
  EXPECT_EQ(uri,
            "s3://minio:miniopass@bucket/somedir/subdir/subfile"
            "?region=us-east-1&scheme=https&endpoint_override="
            "&allow_bucket_creation=0&allow_bucket_deletion=0");
}

fails on Windows MinGW because the bucket is dropped from the URL. I tested it in isolation on this PR:

• Draft: Test exercise Windows CI raulcd/arrow#98

And the failure

 [ RUN      ] S3OptionsTest.MakeUri
D:/a/arrow/arrow/cpp/src/arrow/filesystem/s3fs_test.cc:1747: Failure
Expected equality of these values:
  uri
    Which is: "***somedir/subdir/subfile?region=us-east-1&scheme=https&endpoint_override=&allow_bucket_creation=0&allow_bucket_deletion=0"
  "***bucket/somedir/subdir/subfile" "?region=us-east-1&scheme=https&endpoint_override=" "&allow_bucket_creation=0&allow_bucket_deletion=0"
    Which is: "***bucket/somedir/subdir/subfile?region=us-east-1&scheme=https&endpoint_override=&allow_bucket_creation=0&allow_bucket_deletion=0"

[  FAILED  ] S3OptionsTest.MakeUri (0 ms)

This is because the manual path parsing doesn't take Windows paths into account:

arrow/cpp/src/arrow/filesystem/s3fs.cc

Lines 3051 to 3061 in 546d42c

	Result<std::string> S3FileSystem::MakeUri(std::string path) const {
	if (path.length() <= 1 || path[0] != '/') {
	return Status::Invalid("MakeUri requires an absolute, non-root path, got ", path);
	}
	ARROW_ASSIGN_OR_RAISE(auto uri, util::UriFromAbsolutePath(path));
	if (!options().GetAccessKey().empty()) {
	uri = "s3://" + options().GetAccessKey() + ":" + options().GetSecretKey() + "@" +
	uri.substr("file:///"s.size());
	} else {
	uri = "s3" + uri.substr("file"s.size());
	}

I found out when testing our arrow-s3fs-module-test on all platforms not only on Linux where we have a similar test. This is a pre-existing bug.
Seems to be related to util::UriFromAbsolutePath but haven't been able to pin down the problem due to difficulty testing MinGW.

Component(s)

C++

[raulcd]

Issue resolved by pull request 50205
#50205