[Scons-users] Scons swallowing exception stack trace for jinja2.exceptions.TemplateNotFound

[Mats Wichmann]

On 5/13/24 22:16, Samir Mahaboob Khan Kagadkar via Scons-users wrote:
> Hi SCons Team,
> 
> I use the Jinja2 templating language 
> (https://jinja.palletsprojects.com/en/3.1.x/ 
> <https://jinja.palletsprojects.com/en/3.1.x/>) to generate scripts from 
> within SCons.
> 
> Jinja2 raises the TemplateNotFound (jinja2.exceptions.TemplateNotFound) 
> exception when, say, a file included in the template cannot be found.
> 
> Unfortunately scons does not show the exception stack trace when this is 
> raised as part of a builder.
> 
> Here is a simple SConstruct that demonstrates this:
> 
> import jinja2
> 
>   def small_builder(target, source, env):
> 
>       raise jinja2.exceptions.TemplateNotFound("You should see this 
> message")
> 
>   env=Environment()
> 
> env.Command(['dummy/TEST.COMPLETE'], [], small_builder, chdir=0)
> 
> Here is the output not showing any stack trace:
> 
> $ scons -f <path_to_sconstruct_dir>/SConstruct dummy/TEST.COMPLETE
> 
> scons: Reading SConscript files ...
> 
> scons: done reading SConscript files.
> 
> scons: Building targets ...
> 
> small_builder(["dummy/TEST.COMPLETE"], [])
> 
> scons: done building targets.
> 
> The TemplateNotFound can be raised in a simple standalone python3 script 
> invocation:
> 
> import jinja2
> 
> raise jinja2.exceptions.TemplateNotFound("You should see this message")
> 
> with the below output
> 
> $ python3 test1.py
> 
> Traceback (most recent call last):
> 
>    File "test1.py", line 2, in <module>
> 
>      raise jinja2.exceptions.TemplateNotFound("You should see this message")
> 
> jinja2.exceptions.TemplateNotFound: You should see this message
> 
> Other exceptions work in SCons builders, of course. For example:
> 
> import jinja2
> 
>   def small_builder(target, source, env):
> 
>       #raise jinja2.exceptions.TemplateNotFound("You should see this 
> message")
> 
>       raise ValueError("You should see this message")
> 
>   env=Environment()
> 
> env.Command(['dummy/TEST.COMPLETE'], [], small_builder, chdir=0)
> 
> with the following output:
> 
> scons: Reading SConscript files ...
> 
> scons: done reading SConscript files.
> 
> scons: Building targets ...
> 
> small_builder(["dummy/TEST.COMPLETE"], [])
> 
> scons: *** [dummy/TEST.COMPLETE] ValueError : You should see this message
> 
> Traceback (most recent call last):
> 
>    File “<….>/SCons/Action.py", line 1441, in execute
> 
>      result = self.execfunction(target=target, source=rsources, env=env)
> 
>    File "<….> /SConstruct", line 5, in small_builder
> 
>      raise ValueError("You should see this message")
> 
> ValueError: You should see this message
> 
> scons: building terminated because of errors.

> 
> Could you please take a look?

SCons has a routine which tries to synthesize a BuildError exception 
upon detecting other exceptions that may have been raised during the 
call to the action function.  If doesn't do that right for the jinja 
template exception - which I see is itself synthesized. I don't really 
see how to cause it to do better at the moment.

convert_to_BuildError recognizes the template error as an instance of 
IOError. In that case it tries to do this:

         filename = getattr(status, 'filename', None) 

         strerror = getattr(status, 'strerror', str(status)) 

         errno = getattr(status, 'errno', 2) 

 

         buildError = BuildError( 

             errstr=strerror, 

             status=errno, 

             exitstatus=2, 

             filename=filename, 

             exc_info=exc_info)

the TemplateNotFound has all three attributes that are checked for - set 
to None, so the getattr defaults aren't used. The BuildError thus ends 
up with an error message and status of None, which not surprisingly, 
doesn't yield any interesting message.

I suppose the attribute check could be a little more pedantic, like this:

         strerror = getattr(status, 'strerror', None) 

         if strerror is None: 

             strerror = str(status)

@bdbaddog - any thoughts?