Simplify and unify the {{REVISIONID}} handling code in Parser

Improve documentation for Parser::getRevisionId().

Change-Id: I3cb8721e3bc2e3a06c3158cd60742bc10a458f20

diff --git a/includes/parser/Parser.php b/includes/parser/Parser.php
index c28d842..e6aec34 100644 (file)
--- a/includes/parser/Parser.php
+++ b/includes/parser/Parser.php
@@ -2589,8 +2589,9 @@ class Parser {
                 * Some of these require message or data lookups and can be
                 * expensive to check many times.
                 */
-               if ( Hooks::run( 'ParserGetVariableValueVarCache', [ &$parser, &$this->mVarCache ] )
-                       && isset( $this->mVarCache[$index] )
+               if (
+                       Hooks::run( 'ParserGetVariableValueVarCache', [ &$parser, &$this->mVarCache ] ) &&
+                       isset( $this->mVarCache[$index] )
                ) {
                        return $this->mVarCache[$index];
                }
@@ -2598,24 +2599,6 @@ class Parser {
                $ts = wfTimestamp( TS_UNIX, $this->mOptions->getTimestamp() );
                Hooks::run( 'ParserGetVariableValueTs', [ &$parser, &$ts ] );
 
-               // In miser mode, disable words that always cause double-parses on page save (T137900)
-               static $slowRevWords = [ 'revisionid' => true ]; // @TODO: 'revisiontimestamp'
-               if (
-                       isset( $slowRevWords[$index] ) &&
-                       $this->siteConfig->get( 'MiserMode' ) &&
-                       !$this->mOptions->getInterfaceMessage() &&
-                       // @TODO: disallow this word on all namespaces
-                       $this->nsInfo->isContent( $this->mTitle->getNamespace() )
-               ) {
-                       if ( $this->mRevisionId || $this->mOptions->getSpeculativeRevId() ) {
-                               return '-';
-                       } else {
-                               $this->mOutput->setFlag( 'vary-revision-exists' );
-
-                               return '';
-                       }
-               };
-
                $pageLang = $this->getFunctionLang();
 
                switch ( $index ) {
@@ -2739,23 +2722,35 @@ class Parser {
                                $value = $pageid ?: null;
                                break;
                        case 'revisionid':
-                               # Let the edit saving system know we should parse the page
-                               # *after* a revision ID has been assigned.
-                               $this->mOutput->setFlag( 'vary-revision-id' );
-                               wfDebug( __METHOD__ . ": {{REVISIONID}} used, setting vary-revision-id...\n" );
-                               $value = $this->mRevisionId;
-
-                               if ( !$value ) {
-                                       $rev = $this->getRevisionObject();
-                                       if ( $rev ) {
-                                               $value = $rev->getId();
+                               if (
+                                       $this->siteConfig->get( 'MiserMode' ) &&
+                                       !$this->mOptions->getInterfaceMessage() &&
+                                       // @TODO: disallow this word on all namespaces
+                                       $this->nsInfo->isContent( $this->mTitle->getNamespace() )
+                               ) {
+                                       // Use a stub result instead of the actual revision ID in order to avoid
+                                       // double parses on page save but still allow preview detection (T137900)
+                                       if ( $this->getRevisionId() || $this->mOptions->getSpeculativeRevId() ) {
+                                               $value = '-';
+                                       } else {
+                                               $this->mOutput->setFlag( 'vary-revision-exists' );
+                                               $value = '';
                                        }
-                               }
-
-                               if ( !$value ) {
-                                       $value = $this->mOptions->getSpeculativeRevId();
-                                       if ( $value ) {
-                                               $this->mOutput->setSpeculativeRevIdUsed( $value );
+                               } else {
+                                       # Inform the edit saving system that getting the canonical output after
+                                       # revision insertion requires another parse using the actual revision ID
+                                       $this->mOutput->setFlag( 'vary-revision-id' );
+                                       wfDebug( __METHOD__ . ": {{REVISIONID}} used, setting vary-revision-id...\n" );
+                                       $value = $this->getRevisionId();
+                                       if ( $value === 0 ) {
+                                               $rev = $this->getRevisionObject();
+                                               $value = $rev ? $rev->getId() : $value;
+                                       }
+                                       if ( !$value ) {
+                                               $value = $this->mOptions->getSpeculativeRevId();
+                                               if ( $value ) {
+                                                       $this->mOutput->setSpeculativeRevIdUsed( $value );
+                                               }
                                        }
                                }
                                break;
@@ -5850,6 +5845,11 @@ class Parser {
        /**
         * Get the ID of the revision we are parsing
         *
+        * The return value will be either:
+        *   - a) Positive, indicating a specific revision ID (current or old)
+        *   - b) Zero, meaning the revision ID specified by getCurrentRevisionCallback()
+        *   - c) Null, meaning the parse is for preview mode and there is no revision
+        *
         * @return int|null
         */
        public function getRevisionId() {