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digitalmars.D.bugs - [Issue 7675] New: std.format needs better exception messages

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7675

           Summary: std.format needs better exception messages
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody puremagic.com
        ReportedBy: andrej.mitrovich gmail.com


--- Comment #0 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2012-03-08
17:53:14 PST ---
import std.string;

void main()
{
    string res = format("%s %s", 1);
}

std.format.FormatException std\format.d(62): format error

format() should verify that the count of parameters matches the format
specifier and give a nice error message like this:

std.format.FormatException std\format.d(62): format error: Expected 2
parameters, got 1.

format() is one of the most used functions in Phobos so I think this is pretty
important.

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--- Comment #1 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2012-05-26
09:54:34 PDT ---
If anyone else is annoyed by this you can use a workaround like this:

/** Workaround for Issue 7675 - std.format needs better exception messages */
string safeFmt(string file = __FILE__, int line = __LINE__, T...)(string fmt, T
args)
{
    auto specCount = count(fmt, "%s");
    enforce(specCount == T.length, 
            new Exception(format("Arg count %s doesn't match spec count %s.",
T.length, specCount), file, line));
    return format(fmt, args);
}

That implies using %s exclusively and it only throws on argument count
mismatch, but it's still a shitload better than "Error occurred somewhere, have
fun debugging!".

Throwing exceptions in Phobos with no information on what went wrong should be
*banned*.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs eml.cc


--- Comment #2 from bearophile_hugs eml.cc 2012-05-26 11:57:34 PDT ---
(In reply to comment #1)


     enforce(specCount == T.length, 
             new Exception(format("Arg count %s doesn't match spec count %s.",
 T.length, specCount), file, line));


Andrei wants formatted printing to be sloppy, so currently this doesn't raise
an error:

import std.string;
void main() {
    string res = format("%s ", 1, 2);
}

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--- Comment #3 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2012-05-26
12:42:38 PDT ---
(In reply to comment #2)

 Andrei wants formatted printing to be sloppy, so currently this doesn't raise
 an error..


Right, but the OP code does raise an exception except it gives absolutely no
information whatsoever on what went wrong. Reading a stack trace of a dozen
template instantiations doesn't help either.

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Andrej Mitrovic <andrej.mitrovich gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |WORKSFORME


--- Comment #4 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2013-01-24
16:11:25 PST ---
The situation seems to be better now:

import std.string;
void main()
{
    string res = format("%s %s", 1);
}


 std.format.FormatException D:\dmd-git\dmd2\windows\bin\..\..\src\phobo
\std\format.d(431): Orphan format specifier: %%s %s


Slightly confusing message, as it thought it was going to print '%s' but it
prints the entire string.

And the other message:

import std.string;
void main()
{
    string res = format("%s %s", 1, 2, 3);
}


 std.format.FormatException D:\dmd-git\dmd2\windows\bin\..\..\src\phobos
std\string.d(2536): Orphan format arguments: args[2..3]


I'm quite satisfied that this was implemented. Although the stack trace still
sucks as I've yet to get proper line numbers. 

But at least I don't have to count the specifiers in a wrapper function, I just
have to catch FormatExceptions:

string safeFmt(string file = __FILE__, size_t line = __LINE__, Args...)(string
fmt, Args args)
{
    try
    {
        return format(fmt, args);
    }
    catch (FormatException exc)
    {
        exc.file = file;
        exc.line = line;
        throw exc;
    }
}

void main()
{
    auto x = safeFmt("%s", 1, 2);
}

How great is that?

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Lukasz Wrzosek <luk.wrzosek gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |luk.wrzosek gmail.com


--- Comment #5 from Lukasz Wrzosek <luk.wrzosek gmail.com> 2013-05-22 10:33:44
PDT ---
Why this sample compiles fine if it always frows an exception ?

import std.string;

void main()
{
    string res = format("%s %s", 1);
}

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--- Comment #6 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2013-05-22
14:39:28 PDT ---
(In reply to comment #5)

 Why this sample compiles fine if it always throws an exception ?


Because the string argument is passed at runtime.

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--- Comment #7 from Lukasz Wrzosek <luk.wrzosek gmail.com> 2013-05-24 05:50:11
PDT ---
I know that already, but why it was written like that?
It would be useful to have this kind of error thrown at compile time, wouldn't
it"

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