Add support for previously unimplemented status Page::statusUnique, which adds support for globally unique page names. This commit also changes the the previous commit Page::statusIncomplete to value 128 because it turns out 256 was used in a 3rd party module and it seemed safer to use 128, which was occuped by Page::statusVersions, which has never been used. I've also changed the name of Page::statusIncomplete to Page::statusFlagged since the status indicates an error occurred during last interactive save rather than specifically incomplete.

wire/core/Page.php

@@ -168,24 +168,21 @@ class Page extends WireData implements \Countable, WireMatchable {
 	 * Status levels 1024 and above are excluded from search by the core. Status levels 16384 and above are runtime only and not 
 	 * stored in the DB unless for logging or page history.
 	 *
-	 * If the under 1024 status flags are expanded in the future, it must be ensured that the combined value of the searchable flags 
-	 * never exceeds 1024, otherwise issues in Pages::find() will need to be considered. 
-	 *
 	 * The status levels 16384 and above can safely be changed as needed as they are runtime only. 
 	 * 
-	 * Please note that statuses 2, 32, 256, and 4096 are reserved for future use.
+	 * Please note that all other statuses are reserved for future use.
 	 *
 	 */
 
 	/**
-	 * Base status for pages in use (assigned automatically)
+	 * Base status for pages, represents boolean true (1) or false (0) as flag with other statuses, for internal use purposes only
 	 * #pw-internal
 	 * 
 	 */
 	const statusOn = 1;
-
+	
 	/**
-	 * Reserved status
+	 * Reserved status (internal use)
 	 * #pw-internal
 	 * 
 	 */
@@ -226,18 +223,30 @@ class Page extends WireData implements \Countable, WireMatchable {
 	const statusDraft = 64;
 
 	/**
-	 * Page has version data available (name: "versions").
+	 * Page is flagged as incomplete, needing review, or having some issue
+	 * ProcessPageEdit uses this status to indicate an error message occurred during last internactive save
 	 * #pw-internal
+	 * @since 3.0.127
 	 * 
 	 */
-	const statusVersions = 128;
-
+	const statusFlagged = 128;
+	const statusIncomplete = 128; // alias of statusFlagged
+	
 	/**
-	 * Page might have incomplete data because there were errors when last saved interactively or may be missing required fields
+	 * Deprecated, was never used, but kept in case any modules referenced it
 	 * #pw-internal
+	 * @deprecated
 	 * 
 	 */
-	const statusIncomplete = 256;
+	const statusVersions = 128; 
+	
+	/**
+	 * Reserved for internal use 
+	 * #pw-internal
+	 * @since 3.0.127
+	 *
+	 */
+	const statusInternal = 256;
 
 	/**
 	 * Page is temporary. 1+ day old unpublished pages with this status may be automatically deleted (name: "temp"). 
@@ -309,8 +318,8 @@ class Page extends WireData implements \Countable, WireMatchable {
 		'system' => self::statusSystem,
 		'unique' => self::statusUnique,
 		'draft' => self::statusDraft,
-		'versions' => self::statusVersions,
-		'incomplete' => self::statusIncomplete, 
+		'flagged' => self::statusFlagged, 
+		'internal' => self::statusInternal,
 		'temp' => self::statusTemp,
 		'hidden' => self::statusHidden,
 		'unpublished' => self::statusUnpublished,
@@ -318,6 +327,8 @@ class Page extends WireData implements \Countable, WireMatchable {
 		'deleted' => self::statusDeleted,
 		'systemOverride' => self::statusSystemOverride, 
 		'corrupted' => self::statusCorrupted, 
+		'max' => self::statusMax,
+		'on' => self::statusOn,
 		);
 
 	/**
@@ -1884,9 +1895,11 @@ class Page extends WireData implements \Countable, WireMatchable {
 			if($this->settings['status'] & Page::statusSystemID) $value = $value | Page::statusSystemID;
 			if($this->settings['status'] & Page::statusSystem) $value = $value | Page::statusSystem; 
 		}
-		if($this->settings['status'] != $value) {
+		if($this->settings['status'] != $value && $this->isLoaded) {
 			$this->trackChange('status', $this->settings['status'], $value);
-			$this->statusPrevious = $this->settings['status'];
+			if($this->statusPrevious === null) {
+				$this->statusPrevious = $this->settings['status'];
+			}
 		}
 		$this->settings['status'] = $value;
 		if($value & Page::statusDeleted) {
@@ -3744,6 +3757,7 @@ class Page extends WireData implements \Countable, WireMatchable {
 		$names = array();
 		$remainder = $status;
 		foreach(self::$statuses as $name => $value) {
+			if($value <= self::statusOn || $value >= self::statusMax) continue;
 			if($status & $value) {
 				$names[$value] = $name;
 				$remainder = $remainder & ~$value;

wire/core/PageFinder.php

@@ -209,14 +209,8 @@ class PageFinder extends Wire {
 				$value = $selector->value; 
 				if(!ctype_digit("$value")) {
 					// allow use of some predefined labels for Page statuses
-					if($value == 'hidden') $selector->value = Page::statusHidden;
-						else if($value == 'unpublished') $selector->value = Page::statusUnpublished;
-						else if($value == 'draft') $selector->value = Page::statusDraft;
-						else if($value == 'versions') $selector->value = Page::statusVersions;
-						else if($value == 'locked') $selector->value = Page::statusLocked;
-						else if($value == 'trash') $selector->value = Page::statusTrash;
-						else if($value == 'max') $selector->value = Page::statusMax;
-					else $selector->value = 1;
+					$statuses = Page::getStatuses();
+					$selector->value = isset($statuses[$value]) ? $statuses[$value] : 1;
 				}
 				$not = false;
 				if(($selector->operator == '!=' && !$selector->not) || ($selector->not && $selector->operator == '=')) {
@@ -229,8 +223,8 @@ class PageFinder extends Wire {
 					$selectors[$key] = $this->wire(new SelectorBitwiseAnd('status', $selector->value));
 					
 				} else {
-					$not = $selector->not;
 					// some other operator like: >, <, >=, <=
+					$not = $selector->not;
 				}
 				if(!$not && (is_null($maxStatus) || $selector->value > $maxStatus)) $maxStatus = (int) $selector->value; 
 				

wire/core/PagesEditor.php

@@ -436,6 +436,7 @@ class PagesEditor extends Wire {
 			}
 		}
 
+		$this->pages->names()->checkNameConflicts($page);
 		if(!$this->savePageQuery($page, $options)) return false;
 		$result = $this->savePageFinish($page, $isNew, $options);
 		if($language) $user->language = $language; // restore language

wire/core/PagesNames.php

@@ -3,9 +3,9 @@
 /**
  * ProcessWire Pages Names
  *
- * ProcessWire 3.x, Copyright 2018 by Ryan Cramer
+ * ProcessWire 3.x, Copyright 2019 by Ryan Cramer
  * https://processwire.com
- *
+ * 
  */ 
 
 class PagesNames extends Wire {
@@ -69,7 +69,6 @@ class PagesNames extends Wire {
 	 * @param Page $page
 	 * @param string $format
 	 * @return string Returns page name that was assigned
-	 * @throws WireException
 	 * 
 	 */
 	public function setupNewPageName(Page $page, $format = '') {
@@ -551,6 +550,7 @@ class PagesNames extends Wire {
 			$wheres[] = 'parent_id=:parent_id';
 			$binds[':parent_id'] = $parentID; 
 		}
+		
 		if($pageID) {
 			$wheres[] = 'id!=:id';
 			$binds[':id'] = $pageID;
@@ -654,4 +654,104 @@ class PagesNames extends Wire {
 		return $this->untitledPageName;
 	}
 	
+	/**
+	 * Does given page have a name that has a conflict/collision?
+	 * 
+	 * In multi-language environment this applies to default language only. 
+	 * 
+	 * @param Page $page Page to check
+	 * @return string|bool Returns string with conflict reason or boolean false if no conflict
+	 * @throws WireException If given invalid $options argument
+	 * @since 3.0.127
+	 * 
+	 */
+	public function pageNameHasConflict(Page $page) {
+		
+		$reason = '';
+		
+		$sql = "SELECT id, status, parent_id FROM pages WHERE name=:name AND id!=:id";
+		$query = $this->wire('database')->prepare($sql);
+		$query->bindValue(':name', $page->name);
+		$query->bindValue(':id', $page->id, \PDO::PARAM_INT);
+		$query->execute();
+		
+		if(!$query->rowCount()) {
+			$query->closeCursor();
+			return false;
+		}
+		
+		while($row = $query->fetch(\PDO::FETCH_ASSOC)) {
+			if($row['status'] & Page::statusUnique) {
+				// name is already required to be unique globally
+				$reason = sprintf($this->_("Another page is using name “%s” and requires it to be globally unique"), $page->name);
+			}
+			if((int) $row['parent_id'] === $page->parent_id) {
+				// name already consumed by another page with same parent
+				$reason = sprintf($this->_('Another page with same parent is already using name “%s”'), $page->name);
+			}
+			if($reason) break;
+		}
+		
+		// page requires that it be the only one with this name, so if others have it, then disallow
+		if(!$reason && $page->hasStatus(Page::statusUnique)) {
+			$reason = sprintf($this->_('Cannot use name “%s” as globally unique because it is already used by other page(s)'), $page->name);
+		}
+		
+		$query->closeCursor();
+		
+		return $reason ? $reason : false;
+	}
+
+	/**
+	 * Check given page’s name for conflicts and increment as needed while also triggering a warning notice
+	 * 
+	 * @param Page $page
+	 * @since 3.0.127
+	 * 
+	 */
+	public function checkNameConflicts(Page $page) {
+		
+		$checkName = false;
+		$checkStatus = false;
+		$namePrevious = $page->namePrevious;
+		$statusPrevious = $page->statusPrevious;
+		$isNew = $page->isNew();
+		$nameChanged = !$isNew && $namePrevious !== null && $namePrevious !== $page->name;
+
+		if($isNew || $nameChanged) {
+			// new page or changed name
+			$checkName = true;
+		} else if($statusPrevious !== null && $page->hasStatus(Page::statusUnique) && !($statusPrevious & Page::statusUnique)) {
+			// page just received 'unique' status
+			$checkStatus = true;
+		}
+		
+		if(!$checkName && !$checkStatus) return;
+	
+		do {
+			
+			$conflict = $this->pageNameHasConflict($page);
+			if(!$conflict) break;
+			
+			$this->warning($conflict);
+			
+			if($checkName) {
+				if($nameChanged) {
+					// restore previous name
+					$page->name = $page->namePrevious;
+					$nameChanged = false;
+				} else {
+					// increment name
+					$page->name = $this->incrementName($page->name);
+				}
+				
+			} else if($checkStatus) {
+				// remove 'unique' status
+				$page->removeStatus(Page::statusUnique);
+				break;
+			}
+			
+		} while($conflict);
+	}
+	
 }