eipp: add Allow-Temporary-Remove-of-Essentials

A rather special need option, but the internal planer supports this and
we have a testcase for it & sometimes it is hit (as a bug through). The
option itself mostly serves as a reminder for implementors that they
should be careful with removes and especially temporary removes if they
perform any.

apt-pkg/edsp.cc

@@ -1155,6 +1155,8 @@ bool EIPP::WriteRequest(pkgDepCache &Cache, FileFd &output,		/*{{{*/
       WriteOkay(Okay, output, "Immediate-Configuration: yes\n");
    else if ((flags & Request::NO_IMMEDIATE_CONFIGURATION) != 0)
       WriteOkay(Okay, output, "Immediate-Configuration: no\n");
+   else if ((flags & Request::ALLOW_TEMPORARY_REMOVE_OF_ESSENTIALS) != 0)
+      WriteOkay(Okay, output, "Allow-Temporary-Remove-of-Essentials: yes\n");
    return WriteOkay(Okay, output, "\n");
 }
 									/*}}}*/
@@ -1389,6 +1391,8 @@ bool EIPP::ReadRequest(int const input, std::list<std::pair<std::string,PKG_ACTI
 	    else
 	       flags |= Request::NO_IMMEDIATE_CONFIGURATION;
 	 }
+	 else if (ReadFlag(flags, line, "Allow-Temporary-Remove-of-Essentials:", Request::ALLOW_TEMPORARY_REMOVE_OF_ESSENTIALS))
+	    ;
 	 else
 	    _error->Warning("Unknown line in EIPP Request stanza: %s", line.c_str());
 

apt-pkg/edsp.h

@@ -245,6 +245,7 @@ namespace EIPP								/*{{{*/
       {
 	 IMMEDIATE_CONFIGURATION_ALL = (1 << 0), /*!< try to keep the least amount of packages unconfigured as possible at all times */
 	 NO_IMMEDIATE_CONFIGURATION = (1 << 1), /*!< do not perform immediate configuration at all */
+	 ALLOW_TEMPORARY_REMOVE_OF_ESSENTIALS = (1 << 2), /*!< just as the name suggests, very special case and dangerous! */
       };
    }
 

apt-pkg/packagemanager.cc

@@ -1045,6 +1045,8 @@ pkgPackageManager::OrderResult pkgPackageManager::OrderInstall()
 	 flags |= EIPP::Request::NO_IMMEDIATE_CONFIGURATION;
       else if (_config->FindB("APT::Immediate-Configure-All", false))
 	 flags |= EIPP::Request::IMMEDIATE_CONFIGURATION_ALL;
+      else if (_config->FindB("APT::Force-LoopBreak", false))
+	 flags |= EIPP::Request::ALLOW_TEMPORARY_REMOVE_OF_ESSENTIALS;
 
       if (EIPP::OrderInstall(planer.c_str(), this, flags, nullptr))
 	 return Completed;

cmdline/apt-internal-planer.cc

@@ -152,6 +152,7 @@ int main(int argc,const char *argv[])					/*{{{*/
 		DIE("Parsing the request failed!");
 	_config->Set("APT::Immediate-Configure", (flags & EIPP::Request::NO_IMMEDIATE_CONFIGURATION) == 0);
 	_config->Set("APT::Immediate-Configure-All", (flags & EIPP::Request::IMMEDIATE_CONFIGURATION_ALL) != 0);
+	_config->Set("APT::Force-LoopBreak", (flags & EIPP::Request::ALLOW_TEMPORARY_REMOVE_OF_ESSENTIALS) != 0);
 
 	EDSP::WriteProgress(5, "Read scenario…", output);
 

doc/external-installation-planer-protocol.txt

@@ -162,14 +162,22 @@ The following **preference fields** are supported in request stanzas:
   informational string specifying to which planer this request was send
   initially.
 
-- *Immediate-Configuration:** (option, unset by default) A boolean value
-  defining if the planer should try to configure all packages as quickly
-  as possible (true) or shouldn't perform any kind of immediate
+- **Immediate-Configuration:** (option, unset by default) A boolean
+  value defining if the planer should try to configure all packages as
+  quickly as possible (true) or shouldn't perform any kind of immediate
   configuration at all (false). If not explicitly set with this field
   the planer is free to pick either mode or implementing e.g. a mode
   which configures only packages immediately if they are flagged as
   `Essential` (or are dependencies of packages marked as `Essential`).
 
+- **Allow-Temporary-Remove-of-Essentials** (optional, defaults to `no`).
+  A boolean value allowing the planer (if set to yes) to temporarily
+  remove an essential package. Associated with the APT::Force-LoopBreak
+  configuration option its main use is highlighting that planers who do
+  temporary removes must take special care in terms of essentials. Legit
+  uses of this option by users is very uncommon, traditionally
+  a situation in which it is needed indicates a packaging error.
+
 
 #### Package universe