fix HISTFILE issues (microsoft#168636)

Author: meganrogge

src/vs/workbench/contrib/terminal/browser/media/shellIntegration-rc.zsh

@@ -14,18 +14,23 @@ fi
 # as disable it by unsetting the variable.
 VSCODE_SHELL_INTEGRATION=1
 
+# By default, zsh will set the $HISTFILE to the $ZDOTDIR location automatically. In the case of the
+# shell integration being injected, this means that the terminal will use a different history file
+# to other terminals. To fix this issue, set $HISTFILE back to the default location before ~/.zshrc
+# is called as that may depend upon the value.
+if [[  "$VSCODE_INJECTION" == "1" ]]; then
+	HISTFILE=$USER_ZDOTDIR/.zsh_history
+fi
+
 # Only fix up ZDOTDIR if shell integration was injected (not manually installed) and has not been called yet
 if [[ "$VSCODE_INJECTION" == "1" ]]; then
 	if [[ $options[norcs] = off  && -f $USER_ZDOTDIR/.zshrc ]]; then
 		VSCODE_ZDOTDIR=$ZDOTDIR
 		ZDOTDIR=$USER_ZDOTDIR
+		# A user's custom HISTFILE location might be set when their .zshrc file is sourced below
 		. $USER_ZDOTDIR/.zshrc
 		ZDOTDIR=$VSCODE_ZDOTDIR
 	fi
-
-	if [[ -f $USER_ZDOTDIR/.zsh_history && -z $HISTFILE ]]; then
-		HISTFILE=$USER_ZDOTDIR/.zsh_history
-	fi
 fi
 
 # Shell integration was disabled by the shell, exit without warning assuming either the shell has