How does the dead code elimination work when using args to Printf? If static strings are fed into an empty function, I can imagine it does nothing. However, this I have less of a firm grip upon

  dlg.Printf("the thing.Something is %+v", thing.Something())

And don't misunderstand me: it's a grave pet peeve of mine to do action inside the args to Printf but I can tell you it's a very common [anti-]pattern so I'd presume your users will want a story for how that interacts with the "disappears completely" claim

• 0xFEE1DEAD

  yesterday at 4:54 PM

  In short: You're right - Go will still evaluate argument expressions. In hindsight, I should've made that more obvious, not calling this out initially was an expert blind spot on my part, not an intent to mislead.

  If we consider this example:

    func risky() error {
      return fmt.Errorf("unexpected error")
    }
  
    func risky2() error{
      return fmt.Errorf("also an error")
    }
  
    func main() {
      fmt.Printf("something failed: %v", risky())
      dlg.Printf("something failed: %v", risky2())
    }
  

  And look at the disassembly:

    0x10009f354  d503201f  NOOP                ; Dead code of dlg.Printf
    0x10009f358  b0000000  ADRP 4096(PC), R0   ; Load "also an error" string address
    0x10009f35c  9124ec00  ADD $2363, R0, R0   ; Calculate exact string address
    0x10009f360  d28001a1  MOVD $13, R1        ; Set string length=13 (R1)
    0x10009f364  aa1f03e2  MOVD ZR, R2         ; Clear R2
    0x10009f368  aa1f03e3  MOVD ZR, R3         ; Clear R3
    0x10009f36c  aa0303e4  MOVD R3, R4         ; Clear R4
    0x10009f370  97ffd890  CALL fmt.Errorf(SB) ; Call fmt.Errorf
  

  What disappears is the logging work (formatting, interface/slice plumbing, I/O) and the call itself. Go cannot eliminate calls to functions inside of Printf because they could produce side-effects. Eliminating functions calls like this would be very expensive to do and would clashes with Go's focus on fast compilation times.

  I'll add a section to the README that explains this. Thanks for pointing it out.

• llimllib

  yesterday at 3:16 PM

  It's easy to show that you're right and that code isn't dead so it can't be eliminated:

      package main
      
      import (
       "fmt"
      
       "github.com/vvvvv/dlg"
      )
      
      func risky() error {
       _, err := fmt.Printf("unexpected error\n")
       return err
      }
      
      func main() {
       dlg.Printf("something failed: %s", risky())
       risky()
      }
  

  prints "unexpected error" twice

  • today at 8:56 AM

• exasperaited

  yesterday at 3:46 PM

  This is a thing I had a little "are you sure?" itch in my brain about, but you've expressed so clearly in four lines of comment, and this is me showing gratitude for the comment and the untangling of my brain.

  ETA: Presumably if there was at least an option for passing a closure that would provide a way to address this? Since the closure will only uselessly compile, and not actually uselessly run?

> printf debugging isn't without its annoyances, namely removing the print statements once you're done.

Use something like stacked git[1], and then it's just one "stg pop" and poof, they're gone.

[1] https://stacked-git.github.io/

• BobbyTables2

  yesterday at 1:15 PM

  I’ve been doing this (manually) for about 10+ years.

  I rarely use branches, my local work area is about 50-100 commits on top of master.

  I pick/reorder/edit with “git rebase -i”

  I’ll prefix the commit summary with a word that helps me keep straight debug changes from ones that will go toward a MR.

• shayief

  yesterday at 7:05 PM

  I usually leave them as uncommitted changes, then git checkout to undo them. And using something like `git add -p` to skip Printfs if I need to commit other changes.

> Any feedback is much appreciated.

There is way too much going on in this code whose feature essentially boils down to

    func Printf(f string, v ...any) {
        if CONDITION {
         fmt.Printf(f, v...)
        }
    }

Very cool!

Just one thought: I don't think your stack traces need to include the lines inside Printf itself and it adds to the noise a bit. Maybe just go up to the line where the call to Printf is made?

• 0xFEE1DEAD

  yesterday at 5:32 PM

  Thank you!

  You're absolutely right, it annoys me as well.

  It's a bit finicky to do so, but I'm currently in an exploratory phase of providing an even more fine grained stack tracing feature and filtering out dlg itself is definitly on my todo list.

it doesn't appear to truly be zero cost if you log variables that can't be eliminated. The only way (I believe) to implement zero cost is some type of macro system which go does not support.

• dspillett

  yesterday at 5:09 PM

  > it doesn't appear to truly be zero cost if you log variables that can't be eliminated.

  I'd say it is fair to call it zero cost, if the costs you are seeing are due to the way you are using it. If the values being logged are values you are already computing and storing, constants, or some mix of the two (concatenated via its printf function), by my understanding (caveat: I've never actually used Go myself) all the logging code should be stripped out as dead code in the link stage.

  Obviously if you are performing extra computations with intermediate values to produce the log messages, your code there might produce something that is not reliably detected as eliminable dead code so there would be cost there.

  > The only way (I believe) to implement zero cost is some type of macro system which go does not support.

  That looks to be effectively what it is doing, just at the link stage instead of in a preprocessor. Where C & friends would drop the code inside #ifdef when the relevant value is not set (so it won't be compiled at all) this should throw it out later in the process if DLG_STACKTRACE isn't set at compile time.

  So there will always be a compile-time cost (unlike with a preprocessor macro, something will be produced then thrown away and the analysis of what to throw away will take longer with more code present), but not a run-time cost if the logging is not enabled, assuming you don't have any logic in the trace lines beside the calls to this module.

  • norir

    yesterday at 7:39 PM

    The problem is calling anything zero cost is inherently wrong. Nothing in life has no cost. I know I am being pedantic but I think a more accurate description is "zero production runtime cost," which is also how I interpret rust's zero cost abstraction. In that case too, I find the terminology grating because there are very obviously costs to using rust and its abstractions.

    One obvious cost to code that is removed in production is that there is now a divergence between what your source code says it does and what it actually does. I now need to keep in mind the context the program is running in. There is a cost to that. It might be worth it, but it isn't zero.

• lanstin

  yesterday at 4:06 PM

  Yeah I want a log package where the log statements that don't log also don't have their arguments evaluated. Half of my gc pressure is little strings created to call the log package that don't get logged.

  • 9rx

    yesterday at 4:57 PM

    So what you want is slog, found in the standard library? The doc.go file found in the package even goes into detail about what you (seem to) describe and how it avoids that problem.

    • badc0ffee

      yesterday at 5:42 PM

      A link to doc.go, for the lazy:

      https://cs.opensource.google/go/x/exp/+/645b1fa8:slog/doc.go...

      Basically it says to pass in objects, not prepared strings, so the formatted output is only computed if the message is actually logged. That object can be a struct implementing the LogValuer interface to do any required work/produce formatted output.

      • lanstin

        yesterday at 6:46 PM

        Oh cool, I hadn't run into LogValuer, that's cool. And passing pointers to strings rather than strings, hmmm.

        • 9rx

          yesterday at 7:04 PM

          > And passing pointers to strings rather than strings, hmmm.

          Are you referring to the "URL" example? That isn't a case of passing pointers to strings, that is passing a URL (fmt.Stringer) where the String method has a pointer receiver.

          To demonstrate why the pointer would be needed in that case, consider:

              type URL struct{}
              func (*URL) String() string { return "https://..." }
              func print(v any)           { fmt.Println(v.(fmt.Stringer).String()) }
              func main() {
                  print(&URL{}) // ok
                  print(URL{})  // panic
              }

Cool lib! I took the same approach for my zero cost debugging assertion Go library

https://github.com/negrel/assert

In extreme processing needs, I suppose the elimination of a check that would happen with a level logger is a solid trade off.

My favored approach is a context aware level logger with structured logs going to an aggregator like Splunk.

Because it is context aware, custom filtering logic is available in a middleware.

• jerf

  yesterday at 1:50 PM

  See the standard library "slog" package: https://pkg.go.dev/log/slog

  Which is a relatively recent addition to the Go standard library, based on the collective experience with logging over the years. Compare with the original log standard library: https://pkg.go.dev/log and you can see the changes in even just the time since Go was developed in logging best practices.

  Slog, once you understand the interfaces involved in stuff, has performed most every trick I could desire, up to and including things like subloggers with their own priorities for outputs that override the global settings.

  I'd like to see some slog integration in this package, though I say that without a design in mind. As it stands, this is exactly what it says on the tin; debugging-only output that you fully intend to just disappear out of the production binary.

  The trick it uses is a fairly straightforward use of Go's tag-based compilation features, which I do not mean as a criticism, but to point out that any Go programmer who likes the looks of this but wants to adapt it to their own task will find it easy to simply take the technique directly and adapt it in not very many lines of code.

I'm curious why you prefer this over writing tests.

• 0xFEE1DEAD

  yesterday at 5:00 PM

  I do write tests but I'm not a fan of aiming for 100% coverage because it's incredibly tedious to achieve, and the gains in my experience are marginal.

  That being said even with 100% coverage your code may still contain bugs. If you've never had to debug code with extensive tests then hats off to you.

  • 0points

    today at 9:00 AM

    > I'm not a fan of aiming for 100% coverage

    "100% coverage" is just a measure of line coverage and is highly useless to reason about.

    For testing to become meaningful, you should have test data covering way more than that for the relevant parts.

  • 9rx

    yesterday at 5:34 PM

    When you write a test you see the cute little "debug test" button show up beside it in your editor. If you press it, your logpoints spill the logging information you seek without having to modify the code.

    I expect that is what the parent is really asking about: What does this meaningfully offer over the "built-in" debug logging?

    • 0xFEE1DEAD

      yesterday at 5:53 PM

      Well, my vim is missing buttons like these and I wasn't aware such a feature existed.

      Maybe I'm just old, maybe it's just a different approach, but I built dlg for myself because it fits my workflow.

      > What does this meaningfully offer over the "built-in" debug logging?

      For you, it most likely doesn't offer anything meaningful.

      For devs who use fmt.Printf a lot, it maybe does.

      • latchkey

        yesterday at 6:51 PM

        I'm 52 and coding since I was about 10 years old, so I'm not sure age is the right thing to go off.

  • latchkey

    yesterday at 6:48 PM

    Crazy that I get downvoted for a perfectly valid question, go HN!

    I'm not saying that tests are perfect, but if you do find a bug, you write a new test and fix it. You don't add print statements that you expect to keep around any longer than the amount of effort there is to write the test and fix the code.

    Maybe this product is for people who don't write tests, but even in this codebase, there is a pretty well done set of tests and zero dogfood usage that I noticed.

    • 0xFEE1DEAD

      yesterday at 7:18 PM

      > but if you do find a bug, you write a new test and fix it.

      Maybe there's a misunderstanding here but this library is not meant to replace tests. It's for initially finding the bug for which you then write a test case (or not).

      • latchkey

        yesterday at 7:23 PM

        It isn't clear how this library helps one find bugs.

        • danudey

          yesterday at 8:28 PM

          If you're not sure how logging debug information can help you find bugs then I'm not sure what to say. Especially if you've been programming for four decades, I would think it would be obvious how logging information can help you find logic or data errors in your code/inputs/outputs.

          • latchkey

            yesterday at 8:31 PM

            I know how to write failing tests, and use a debugger.

    • danudey

      yesterday at 8:26 PM

      I think you're getting downvoted because it's not a valid question - debug logging and unit testing are two separate things, and the OP didn't say anywhere that he prefers this to unit tests. Your question presupposes a dichotomy that doesn't exist.

      • latchkey

        yesterday at 8:35 PM

        My statement certainly had some implied subtext that I can expand upon now...

        If you write tests, you don't need a specialized library for debug logging.

        Run the test, and set a breakpoint in your debugger.

        • danudey

          yesterday at 9:22 PM

          This is only mildly offtopic, but I wonder if the following is true:

          Software developers who...

          1. Experienced actual instruction on software development;

          2. Learned to write software in C/C++/FORTRAN/Pascal/whatever; or

          3. Spent a lot of time in more niche situations like system programming, embedded programming, enterprise systems, etc.

          ...are familiar with using debuggers as part of their workflow to inspect internal state and diagnose. In contrast, developers who...

          1. Were entirely self-taught;

          2. Grew up on interpreted languages (JS, Python, PHP, Perl, etc); and

          3. Generally tend to write smaller, self-contained projects

          ...tend to just add debug logging and re-run the program.

          I definitely have used debuggers in the past, but as someone who almost exclusively has written in interpreted languages (or languages where the write-compile-run loop is fast, e.g. Golang), my habit is to add debug logging to more places to validate internal state as the program runs, rather than attaching a debugger and inspecting specific things manually.

          Either way, I think it's two separate approaches and I think in different circumstances there are definitely benefits to one or the other. In most of my Python scripts it's faster to add a `print(f"variable is {variable}")` than it would be to attach a debugger; also for a small script that's only going to run a few times, or run very occasionally, writing unit tests is often overkill because often the entire script is effectively a unit.

          • latchkey

            yesterday at 11:47 PM

            I don’t know if you’re trying to make assumptions about me or you, but I am those 3 things.

            It is definitely different approaches and both can achieve the same goals, but having started with your approach and then learned IDE’s, debugging and writing tests, I can from my own experience say that tests and debuggers are the way to go when it comes to building long term stable applications, especially in shared environments.

            As for speed to attach a debugger? Lol, it is one button click in a proper IDE and the speed and utility of figuring out the solution is faster. What I am hearing from you is that you’re unwilling to put the time into learning/using the tools. Or maybe you’re just stuck in your own headspace, many developers get that way, it is why we have editor wars and whatnot.