Re: GNU make troubleshooting

[Alejandro Colomar]

Hi Paul,

On 2023-08-26 18:48, Paul Smith wrote:
> I added a new appendix to the GNU make manual for troubleshooting help;
> I haven't pushed it yet.  See below.  Comments welcome.
> 
> I think the outline you provided earlier, Bruno, has the problem that a
> lot of it isn't really about troubleshooting per se, it's about how to
> write makefiles in general.  I tried to restrict this specifically to
> describing the types of problems you might see and the steps you might
> take to troubleshoot them.
> 
> I'm thinking of adding another chapter on hints and tips for writing
> good makefiles.
> 
> -----------------
> Appendix C Troubleshooting Make and Makefiles
> *********************************************
> 
> Troubleshooting 'make' and makefiles can be tricky.  There are two
> reasons: first, makefiles are not procedural programs and many users are
> used to procedural languages and scripts.  Second, makefiles consist of
> two different syntaxes in one file: makefile syntax, that 'make' reads,
> and shell syntax, which is sent to a shell program for parsing and
> execution.
> 
>    If you have problems with GNU Make, first consider the type of
> problem you are having.  Problems will generally be in one of these
> categories:
> 
>    * A syntax or other error was reported when 'make' attempted to parse
>      your makefiles.
> 
>    * A command that 'make' invoked failed (exited with a non-0 exit
>      code).
> 
>    * The command that 'make' invoked was not the one you expected.
> 
>    * 'make' was not able to find a rule to build a target.
> 
>    * 'make' rebuilds a target that you didn't think was out of date.
> 
>    * Or, 'make' did not rebuild a target that you expected it to build.
> 
>    The strategies for troubleshooting differ for different types of
> problems.  For issues related to how makefiles are parsed, strategies
> include:
> 
>    * Using the '-p' option to show the makefile database, after
>      evaluation (*note Summary of Options: Options Summary.).
> 
>    * Using the 'info' function to understand how elements of the
>      makefile are expanded (*note Functions That Control Make: Make
>      Control Functions.).
> 
>    For issues related to how rules are applied, strategies include:
> 
>    * Removing the '@' prefix from recipes, so you can see the commands
>      make is invoking to rebuild the target (*note Recipe Echoing:
>      Echoing.).
> 
>    * Using the '--trace' option to explain which rules 'make' invokes
>      and why (*note Summary of Options: Options Summary.).
> 
>    * Using the '--debug=v,i' or '-d' options to show how 'make' is
>      determining which recipes should be used, or why targets do not
>      need to be rebuilt (*note Summary of Options: Options Summary.).
> 
> * Menu:
> 
> * Parse Error::                 Syntax errors when parsing makefiles.
> * Command Failure::             Recipe commands exit with error codes.
> * Wrong Rule::                  'make' chooses the wrong rule.
> * No Rule Found::               No rule was found to build a target.
> * Extra Rebuilds::              Targets are rebuilt unnecessarily.
> * Missing Rebuilds::            Out-of-date targets are not rebuilt.
> * Troubleshooting Strategies::  Strategies used for troubleshooting issues.
> 
> 
> C.1 Errors When Parsing Makefiles
> =================================
> 
> This type of error is the simplest to resolve.  The error output you
> will see will have a format like this:
> 
>      Makefile:10: *** missing separator.  Stop.
> 
>    This message gives you all the information you need to address the
> error: it gives the name of the makefile (here 'Makefile') and the line
> number (here '10') in that makefile where GNU Make's parser failed.
> Following that is a description of the error.  Further explanations of
> these error messages can be found in *note Errors Generated by Make:
> Error Messages.
> 

When using .SECONDEXPANSION, this becomes a bit more tricky.  It would
be interesting to recommend to put an $(info $(SUSPECT_VARIABLE)) right
before lines where you don't see the issue at first glance.

You already mention $(info) in the overview above, but I think a
reminder here might be useful.

Cheers,
Alex



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