add --preremove option

Allows adding and removing packages within a single transaction. This is
particularly useful for complicated conflicts that ALPM cannot resolve
on its own, e.g.:

https://archlinux.org/news/linux-firmware-2025061312fe085f-5-upgrade-requires-manual-intervention/

Currently, dealing with these situations requires doing something
complicated like bypassing dependency checking to break and then repair
the database in two separate steps. By allowing installation and removal
within a single transaction no bypass is required:

 pacman -Syu --preremove linux-firmware linux-firmware

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>

doc/pacman.8.asciidoc

@@ -292,6 +292,9 @@ Upgrade Options (apply to '-S' and '-U')[[UO]]
 	exclamation mark. Subsequent matches will override previous ones. A leading
 	literal exclamation mark or backslash needs to be escaped.
 
+*\--preremove <package>::
+	Uninstall 'package' before performing the requested installation. Multiple
+	packages can be specified by separating them with commas.
 
 Query Options (apply to '-Q')[[QO]]
 -----------------------------------

src/pacman/conf.c

@@ -150,6 +150,7 @@ int config_free(config_t *oldconfig)
 	FREELIST(oldconfig->noupgrade);
 	FREELIST(oldconfig->noextract);
 	FREELIST(oldconfig->overwrite_files);
+	FREELIST(oldconfig->preremove);
 	free(oldconfig->configfile);
 	free(oldconfig->sysroot);
 	free(oldconfig->rootdir);

src/pacman/conf.h

@@ -134,6 +134,8 @@ typedef struct __config_t {
 	/* our connection to libalpm */
 	alpm_handle_t *handle;
 
+	alpm_list_t *preremove;
+
 	alpm_list_t *explicit_adds;
 	alpm_list_t *explicit_removes;
 
@@ -214,7 +216,8 @@ enum {
 	OP_REFRESH,
 	OP_ASSUMEINSTALLED,
 	OP_DISABLEDLTIMEOUT,
-	OP_DISABLESANDBOX
+	OP_DISABLESANDBOX,
+	OP_PREREMOVE,
 };
 
 /* clean method */

src/pacman/pacman.c

@@ -196,6 +196,8 @@ static void usage(int op, const char * const myname)
 				addlist(_("      --ignore <pkg>   ignore a package upgrade (can be used more than once)\n"));
 				addlist(_("      --ignoregroup <grp>\n"
 				          "                       ignore a group upgrade (can be used more than once)\n"));
+				addlist(_("      --preremove <pkg>\n"));
+				addlist(_("                       uninstall <pkg> before performing installation\n"));
 				__attribute__((fallthrough));
 			case PM_OP_REMOVE:
 				addlist(_("  -d, --nodeps         skip dependency version checks (-dd to skip all checks)\n"));
@@ -770,6 +772,9 @@ static int parsearg_upgrade(int opt)
 		case OP_IGNOREGROUP:
 			parsearg_util_addlist(&(config->ignoregrp));
 			break;
+		case OP_PREREMOVE:
+			parsearg_util_addlist(&(config->preremove));
+			break;
 		case OP_DOWNLOADONLY:
 		case 'w':
 			config->op_s_downloadonly = 1;
@@ -982,6 +987,7 @@ static int parseargs(int argc, char *argv[])
 		{"color",      required_argument, 0, OP_COLOR},
 		{"disable-download-timeout", no_argument, 0, OP_DISABLEDLTIMEOUT},
 		{"disable-sandbox", no_argument, 0, OP_DISABLESANDBOX},
+		{"preremove", required_argument, 0, OP_PREREMOVE},
 		{0, 0, 0, 0}
 	};
 

src/pacman/sync.c

@@ -717,6 +717,21 @@ static int sync_trans(alpm_list_t *targets)
 		}
 	}
 
+	for(i = config->preremove; i; i = i->next) {
+		alpm_pkg_t *pkg;
+		const char *pname = i->data;
+		alpm_db_t *db_local = alpm_get_localdb(config->handle);
+
+		if((pkg = alpm_db_get_pkg(db_local, pname)) != NULL) {
+			if(alpm_remove_pkg(config->handle, pkg) == -1) {
+				alpm_errno_t err = alpm_errno(config->handle);
+				pm_printf(ALPM_LOG_ERROR, "'%s': %s\n", pname, alpm_strerror(err));
+				retval = 1;
+			}
+			config->explicit_removes = alpm_list_add(config->explicit_removes, pkg);
+		}
+	}
+
 	if(retval) {
 		trans_release();
 		return retval;