[curl] Default features not getting disabled, using a specific SSL backend is basically impossible

[glorantq]

Is your feature request related to a problem? Please describe.

When in manifest mode, default features cannot be disabled. Having this as a dependency in my vcpkg.json:
{ "name": "curl", "default-features": false },
I see that curl is getting build with the default options still enabled: curl[core,non-http,sectransp,ssl]. This makes it impossible to build only for http usage, and to select a custom SSL backend.

Furthermore, the http2 option also forces the default ssl backend, which again, makes it impossible to use a specific backend exclusively.

Proposed solution

The expected behaviour would be that the default-features switch works, and the http2 option shouldn't depend on the default ssl backend feature, when a custom ssl backend is enabled.

Describe alternatives you've considered

No response

Additional context

Building with options: "mbedtls", "http2", "brotli", "zstd", "tool", output of curl -V
Actual:

curl 8.2.0-DEV (Darwin) libcurl/8.2.0-DEV SecureTransport (mbedTLS/2.28.1) zlib/1.2.13 brotli/1.0.9 zstd/1.5.5 nghttp2/1.55.1
Release-Date: [unreleased]
Protocols: dict file ftp ftps gopher gophers http https imap imaps mqtt pop3 pop3s rtsp smb smbs smtp smtps telnet tftp
Features: alt-svc AsynchDNS brotli HSTS HTTP2 HTTPS-proxy IPv6 Largefile libz MultiSSL NTLM SSL threadsafe UnixSockets zstd

Expected (with modified vcpkg.json for the port):

curl 8.2.0-DEV (Darwin) libcurl/8.2.0-DEV mbedTLS/2.28.1 zlib/1.2.13 brotli/1.0.9 zstd/1.5.5 nghttp2/1.55.1
Release-Date: [unreleased]
Protocols: http https
Features: alt-svc AsynchDNS brotli HSTS HTTP2 HTTPS-proxy IPv6 Largefile libz NTLM SSL threadsafe UnixSockets zstd

[jimwang118]

The content of the local test file is as follows:
vcpkg.json

{
  "name": "test",
  "version-string": "no-version",
  "dependencies": [
    {
      "name": "curl",
      "default-features": false   
    }
  ]
}

test.cpp

#include <iostream>
#include <fstream>
#include <sstream>
#include <curl/curl.h>

int main()
{
    cout << "verions:" << endl;
    return 0;
}

cmakelists.txt
cmake_minimum_required(VERSION 3.8)

project(test)

# Add source to this project's executable.
add_executable (test "test.cpp")

find_package(CURL CONFIG REQUIRED)
    target_link_libraries(test PRIVATE CURL::libcurl)

After compiling, the result is as expected, and only the curl library is installed locally. The default-features: non-http and ssl will not be installed.

[glorantq]

Upon further investigation, I see that another dependency, curlpp is causing the mentioned features to be enabled. While it's weird for a cURL wrapper to directly request features for cURL, it's not a bug with the cURL port, sorry.

The issues with the http2 feature forcing the default ssl backend still stand.