CURLINFO_USED_PROXY: return bool whether the proxy was used

Adds test536 to verify

Closes #12719

docs/libcurl/curl_easy_getinfo.md

@@ -120,6 +120,10 @@ See CURLINFO_PRETRANSFER_TIME_T(3)
 Time during which this transfer was held in a waiting queue.
 See CURLINFO_QUEUE_TIME_T(3)
 
+## CURLINFO_USED_PROXY
+
+Whether the proxy was used (Added in 8.7.0). See CURLINFO_USED_PROXY(3)
+
 ## CURLINFO_STARTTRANSFER_TIME
 
 Time from start until just when the first byte is received.

docs/libcurl/opts/CURLINFO_USED_PROXY.md

@@ -0,0 +1,69 @@
+---
+c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
+SPDX-License-Identifier: curl
+Title: CURLINFO_USED_PROXY
+Section: 3
+Source: libcurl
+See-also:
+  - CURLOPT_NOPROXY (3)
+  - CURLOPT_PROXY (3)
+  - curl_easy_getinfo (3)
+  - curl_easy_setopt (3)
+---
+
+# NAME
+
+CURLINFO_USED_PROXY - whether the transfer used a proxy
+
+# SYNOPSIS
+
+~~~c
+#include <curl/curl.h>
+
+CURLcode curl_easy_getinfo(CURL *handle, CURLINFO_USED_PROXY,
+                           long *authp);
+~~~
+
+# DESCRIPTION
+
+Pass a pointer to a long. It gets set to zero set if no proxy was used in the
+previous transfer or a non-zero value if a proxy was used.
+
+# PROTOCOLS
+
+HTTP(S)
+
+# EXAMPLE
+
+~~~c
+int main(int argc, char *argv[])
+{
+  CURL *curl = curl_easy_init();
+  if(curl) {
+    CURLcode res;
+    curl_easy_setopt(curl, CURLOPT_URL, argv[1]);
+    curl_easy_setopt(curl, CURLOPT_PROXY, "http://127.0.0.1:80");
+    curl_easy_setopt(curl, CURLOPT_NOPROXY, "example.com");
+
+    res = curl_easy_perform(curl);
+
+    if(!res) {
+      /* extract the available proxy authentication types */
+      long used;
+      res = curl_easy_getinfo(curl, CURLINFO_USED_PROXY, &used);
+      if(!res) {
+        printf("The proxy was %sused\n", used ? "": "NOT ");
+      }
+    }
+    curl_easy_cleanup(curl);
+  }
+}
+~~~
+
+# AVAILABILITY
+
+Added in 8.7.0
+
+# RETURN VALUE
+
+Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.

docs/libcurl/opts/Makefile.inc

@@ -95,6 +95,7 @@ man_MANS =                                      \
   CURLINFO_TLS_SSL_PTR.3                        \
   CURLINFO_TOTAL_TIME.3                         \
   CURLINFO_TOTAL_TIME_T.3                       \
+  CURLINFO_USED_PROXY.3                         \
   CURLINFO_XFER_ID.3                            \
   CURLMOPT_CHUNK_LENGTH_PENALTY_SIZE.3          \
   CURLMOPT_CONTENT_LENGTH_PENALTY_SIZE.3        \

docs/libcurl/symbols-in-versions

@@ -506,6 +506,7 @@ CURLINFO_TLS_SSL_PTR            7.48.0
 CURLINFO_TOTAL_TIME             7.4.1
 CURLINFO_TOTAL_TIME_T           7.61.0
 CURLINFO_TYPEMASK               7.4.1
+CURLINFO_USED_PROXY             8.7.0
 CURLINFO_XFER_ID                8.2.0
 CURLIOCMD_NOP                   7.12.3
 CURLIOCMD_RESTARTREAD           7.12.3