Rename lastDirectoryIsRemote to lastDirectoryisUnsuitableForOldPWD and add...

Rename lastDirectoryIsRemote to lastDirectoryisUnsuitableForOldPWD and add some comments. I always find this code hard to analyze.

sources/PTYSession.m

@@ -163,7 +163,7 @@ static NSString *const SESSION_ARRANGEMENT_DIRECTORIES = @"Directories";  // Arr
 static NSString *const SESSION_ARRANGEMENT_HOSTS = @"Hosts";  // Array of VT100RemoteHost
 static NSString *const SESSION_ARRANGEMENT_CURSOR_GUIDE = @"Cursor Guide";  // BOOL
 static NSString *const SESSION_ARRANGEMENT_LAST_DIRECTORY = @"Last Directory";  // NSString
-static NSString *const SESSION_ARRANGEMENT_LAST_DIRECTORY_IS_REMOTE = @"Last Directory Is Remote";  // BOOL
+static NSString *const SESSION_ARRANGEMENT_LAST_DIRECTORY_IS_UNSUITABLE_FOR_OLD_PWD = @"Last Directory Is Remote";  // BOOL
 static NSString *const SESSION_ARRANGEMENT_SELECTION = @"Selection";  // Dictionary for iTermSelection.
 static NSString *const SESSION_ARRANGEMENT_APS = @"Automatic Profile Switching";  // Dictionary of APS state.
@@ -232,7 +232,7 @@ static const NSUInteger kMaxHosts = 100;
 @property(nonatomic) NSTimeInterval lastResize;
 @property(atomic, assign) PTYSessionTmuxMode tmuxMode;
 @property(nonatomic, copy) NSString *lastDirectory;
-@property(nonatomic) BOOL lastDirectoryIsRemote;
+@property(nonatomic) BOOL lastDirectoryIsUnsuitableForOldPWD;
 @property(nonatomic, retain) VT100RemoteHost *lastRemoteHost;  // last remote host at time of setting current directory
 @property(nonatomic, retain) NSColor *cursorGuideColor;
 @property(nonatomic, copy) NSString *badgeFormat;
@@ -1272,7 +1272,7 @@ ITERM_WEAKLY_REFERENCEABLE
         if (arrangement[SESSION_ARRANGEMENT_LAST_DIRECTORY]) {
             [aSession->_lastDirectory autorelease];
             aSession->_lastDirectory = [arrangement[SESSION_ARRANGEMENT_LAST_DIRECTORY] copy];
-            aSession->_lastDirectoryIsRemote = [arrangement[SESSION_ARRANGEMENT_LAST_DIRECTORY_IS_REMOTE] boolValue];
+            aSession->_lastDirectoryIsUnsuitableForOldPWD = [arrangement[SESSION_ARRANGEMENT_LAST_DIRECTORY_IS_UNSUITABLE_FOR_OLD_PWD] boolValue];
         }
     }
@@ -4033,7 +4033,7 @@ ITERM_WEAKLY_REFERENCEABLE
         result[SESSION_ARRANGEMENT_CURSOR_GUIDE] = @(_textview.highlightCursorLine);
         if (self.lastDirectory) {
             result[SESSION_ARRANGEMENT_LAST_DIRECTORY] = self.lastDirectory;
-            result[SESSION_ARRANGEMENT_LAST_DIRECTORY_IS_REMOTE] = @(self.lastDirectoryIsRemote);
+            result[SESSION_ARRANGEMENT_LAST_DIRECTORY_IS_UNSUITABLE_FOR_OLD_PWD] = @(self.lastDirectoryIsUnsuitableForOldPWD);
         }
         result[SESSION_ARRANGEMENT_SELECTION] =
             [self.textview.selection dictionaryValueWithYOffset:-numberOfLinesDropped];
@@ -8357,7 +8357,9 @@ ITERM_WEAKLY_REFERENCEABLE
     }
 }
-- (void)setLastDirectory:(NSString *)lastDirectory isRemote:(BOOL)isRemote {
+// isRemote is a misnomer. It's really "is unsuitable for old PWD", since it would be YES for
+// when shell integration had never been used and the lastDirectory is not updated reliably.
+- (void)setLastDirectory:(NSString *)lastDirectory isUnsuitableForOldPWD:(BOOL)isUnsuitableForOldPWD {
     DLog(@"Set last directory to %@", lastDirectory);
     if (lastDirectory) {
         [_directories addObject:lastDirectory];
@@ -8365,12 +8367,12 @@ ITERM_WEAKLY_REFERENCEABLE
     }
     [_lastDirectory autorelease];
     _lastDirectory = [lastDirectory copy];
-    _lastDirectoryIsRemote = isRemote;
+    _lastDirectoryIsUnsuitableForOldPWD = isUnsuitableForOldPWD;
     [_delegate sessionCurrentDirectoryDidChange:self];
 }
 - (NSString *)currentLocalWorkingDirectory {
-    if (_lastDirectoryIsRemote || _lastDirectory == nil) {
+    if (_lastDirectoryIsUnsuitableForOldPWD || _lastDirectory == nil) {
         // Ask the kernel what the child's process's working directory is.
         return [_shell getWorkingDirectory];
     } else {
@@ -8400,7 +8402,10 @@ ITERM_WEAKLY_REFERENCEABLE
     [[iTermShellHistoryController sharedInstance] recordUseOfPath:directory
                                                            onHost:[_screen remoteHostOnLine:line]
                                                          isChange:!isSame];
-    [self setLastDirectory:directory isRemote:!remoteHost.isLocalhost];
+    // Note that when remoteHost is nil, it's unsuitable for old PWD because
+    // that means shell integration hasn't been used and we have to keep
+    // pulling the pwd from the child process via the kernel.
+    [self setLastDirectory:directory isUnsuitableForOldPWD:!remoteHost.isLocalhost];
     self.lastRemoteHost = remoteHost;
 }