Category: Apple

In a macOS programming project I have a command that allows the user to open a file containing some configuration options. This file is a property list, so the contents were being read using NSDictionary(contentsOf:); this method simply returns nil if an error occurs. I wanted to provide more details about the failure than simply “The file could not be read”, so I looked for a Foundation method that would throw an NSError. I settled on FileHandle(forReadingFrom:) and inserted the following code:

    do {
        _ = try FileHandle(forReadingFrom: url)
    }
    catch let error as NSError {
        let alert = NSAlert()
        alert.messageText = "An error occurred while reading the options file.".localized()
        alert.informativeText = error.localizedDescription
        alert.beginSheetModal(for: mainWindow) { (response) in
            if response == NSAlertSecondButtonReturn {
                OperationQueue.main.addOperation { self.resetOptions(nil) }
            }
        }
        return
    }

Then I set up a few test cases, including a file that was owned by another user (with no read permission). To my surprise, the error description implied that I was unable to write the file:

[application icon redacted]

…and while that’s also true, that’s certainly not the error I expected to get.

I looked at the error object in the debugger, and sure enough, the error code was 513 (NSFileWriteNoPermissionError) and not 257 (NSFileReadNoPermissionError). Weird.

Well, I know I’m trying to read the file, and I don’t want to confuse the user, so I changed the catch clause to handle this case:

    catch var error as NSError {
        if error.code == NSFileWriteNoPermissionError {
            error = NSError(domain: NSCocoaErrorDomain, code: NSFileReadNoPermissionError, userInfo: error.userInfo)
        }
        let alert = NSAlert()
        //...
        return
    }

…and that seemed to do nicely. But I can’t find any documentation on whether this is expected behavior or what I might be doing wrong.

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UPDATE: The bug described below is fixed in macOS 10.12.4 and the workaround described is no longer necessary (except for backward compatibility).

In a recent macOS project I have an NSTextField that contains text with tab characters in order to display a data table. (The text is an NSAttributedString to which I apply an NSParagraphStyle with its tabStops property set to an array containing a number of right-aligned NSTextTabs.)

The text field was drawn as intended (with the text aligned to the tab stops) before upgrading to 10.12.2. After upgraded, the text was no longer aligned to the tab stops, and when using monospacedDigitSystemFont there were cosmetic glitches displayed as well:

Under time pressure for a release, I implemented the workaround of replacing the NSTextField with an NSTextView. (I did this dynamically since it is not obvious how to create “bare” NSTextViews in Xcode’s Interface Builder.) Using an NSTextView I was able to get the data table to display as I had intended.

When writing up this bug (#29758498; Radar, Open Radar) I tried to create a simple test case that would illustrate the issue, but on my first try to recreate the problem from scratch, the issue didn’t appear. Puzzled, I copied the code and .xib file from my application into the test project, and was able to reproduce the issue.

By examining the text of the .xib files, I discovered that my newly created .xib file has a content view with wantsLayer=”YES”, and in this case the NSTextField works as intended under 10.12.2; but the .xib file from my application (which was created before Xcode 8 was released) did not have a layer set on the content view, and this did not work under 10.12.2 (although it had worked fine on 10.12.1 and earlier). Setting a layer on the application’s window’s content view (in the View Effects tab of the Assistant Editor in Xcode) was enough to fix the issue and make the table display as intended:

(Yes, bridge players, those point counts are bogus; my test program is generating random values to insert into the table.)

My wider questions are:

1. What happened? We know there were a lot of graphic updates in 10.12.2, but it’s odd that the problem only occurs with the system font. I haven’t investigated whether the font file itself has changed.
2. I can’t believe I’m the only person that’s run into this (although my usual googling produced no other hits). Is this really an uncommon case? Or is this a(nother) gap in Apple’s test suite?
3. If Apple is expecting that the default case for content views is to have wantsLayer set, then it should certainly make this more widely known. I couldn’t find any references to this issue in the AppKit release notes.

2 Comments

My previous post illustrating a technique for restoring the current working directory in Apple’s Terminal for tcsh users was discovered by Khoo Yit Phang, who suggested an improved version down in the comments. I’m reproducing it here for greater visibility:

if ("$?TERM_PROGRAM") then
  if ("$TERM_PROGRAM" == "Apple_Terminal") then
    alias cwdcmd '( set echo_style = both; echo -n "33]7;file://${host}${cwd:ags/ /%20/}a" )'
    cwdcmd
  endif
endif

Compared to my approach, it has two improvements: (1) by using cwdcmd (of which I was previously unaware) rather than precmd, it only runs when you actually change directories; and (2) by using a suitably configured echo, it avoids running an external command (printf is not built into tcsh, but is present in /usr/bin).

Thanks, Yit.

Update: Of course, with this technique you have to explicitly run the command once, to restore the working directory to the title bar for the first time when you start up. Fixed above.

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In John Siracusa’s excellent review of OS X Mavericks, he (originally) mentioned that the Terminal application is able to restore the current working directory of open shells across launches.

However, this section has subsequently disappeared from the online version, perhaps for the reasons given below (update: see below). Try looking here for a cached version of the original; scroll down to page/slide number 94. Sorry, John. Please purchase the full review on the iBooks store or the Amazon Kindle store to support John’s work.

Of course I was excited to try this out as, in the course of my work as a software developer, I often have several shell windows open in specific directories. So I tried it, and it didn’t work. It turns out the built-in support supplied by Apple assumes that you’re using the bash shell, but as an old-timer I’m stuck on tcsh instead:

@rsfinn Me too, but that's why. Try a new user account with bash and it should work.

— John Siracusa (@siracusa) October 24, 2013

Well, that’s no good, I thought. So I looked in the supporting code’s implementation (/etc/bashrc), and figured out how to do the same thing in tcsh. Simply place the following in your .tcshrc file:

if ("$?TERM_PROGRAM") then
 if ("$TERM_PROGRAM" == "Apple_Terminal") then
  alias precmd 'printf "33]7;%sa" "file://$host$cwd:ags/ /%20/"'
 endif
endif

This uses the appropriate escape sequence to send the URL of the current working directory to the terminal before each command; Terminal detects this information and uses it to update the state of the window (including a proxy icon in the window’s title bar for the corresponding folder). It turns out that the key is doing it using precmd (tcsh’s equivalent of PROMPT_COMMAND), and not sending the sequence in the prompt string itself as one might think. (The outer if statement is necessary to avoid an error when remotely logging in, as with ssh. It has to be a separate statement because of the variable expansion rules in tcsh.)

I’ve notified John via Twitter, so perhaps he add restore this information back to his review. In any case, it’s documented here for future generations. Drop me a note below if you have any issues with it.

Update: It turns out John removed it because he discovered it was a feature in Mountain Lion as well, which had happened not to work on his machine:

@kevinglowacz I did, after (finally) determining that it's not new in Mavericks. Major confusion there. My apologies.

— John Siracusa (@siracusa) October 25, 2013

@plastikhu That wasn't the problem on my end, actually. Turns out I'd modified files under /etc long ago on the 10.8 Mac I was testing on…

— John Siracusa (@siracusa) October 25, 2013

If you listen to John’s podcasts, you’ll realize that makes sense: he wouldn’t let something not new in Mavericks stand in the Mavericks review. Regardless, I wasn’t aware of the feature before and it still wouldn’t have worked in tcsh, so this post is presumably still useful. (Note that I haven’t tried it on Mountain Lion, and I’ve already upgraded my working machines to Mavericks; I don’t know why this technique wouldn’t work on Mountain Lion, but use it at your own risk.)

Update 2: OK, so it turns out the feature was first implemented in Lion, and other people have already figured out how to port it to other shells; see here for an implementation in zsh, for example. How did I manage to not learn about this for the last two years? Oh, well…

5 Comments