Support curl from a snap (#3329)

plugins/python-build/bin/python-build

@@ -458,7 +458,14 @@ http_head_curl() {
 }
 
 http_get_curl() {
-  curl -q -o "${2:--}" -sSLf ${CURL_OPTS} "$1"
+  local out;
+  # Curl is also available as a snap. Snaps cannot read or write /tmp
+  # (files cannot be found, any write result is silently discarded).
+  local curl_is_snap;
+  if [[ $(command -v curl) == "/snap/"* ]]; then curl_is_snap=1; fi
+  if [[ -n $2 && -n $curl_is_snap ]]; then out="$HOME/$(basename "$2")"; else out="$2"; fi
+  curl -q -o "${out:--}" -sSLf ${CURL_OPTS} "$1" || return $?
+  if [[ -n $out && -n $curl_is_snap ]]; then mv "$out" "$2"; fi
 }
 
 http_head_wget() {