Failsafe tonel

[privat]

The tonel format expects that the definition of a method is a sane superset of Pharo/Smalltalk.

The idea is that the resulting files looks like some classic source files from some classic programming languages that can easily be visualized, merged, hacked, etc. by humans. Instead of a random serialization format.

However, the current format cannot deal with method using some extended syntax that does not conform to the ad hoc rules of the tonel method content. Worse, tonel will blindly accept to save those methods not following those rules, thus creating files that won't be readable.
As a simple illustrative example, we can imagine weird fancy literals: for interpolation, for regex, for new separators that just will break the format. E.g foo ^ '#[ $' ]' or bar ^ ##/"hell/ or foo ^ «french][style» or whatever Pharo users want to experiment.
Also, it cannot deal with methods containing some syntax errors without corruption of the whole file, thus preventing the reparation of the offending methods.

Because of the current format with [] and a content that must follow some specific matching rules, there is no easy way to adapt it to be compatible with an extended, more robust format.
We want neither to change radically the format, nor losing the good human-related features.
Therefore, I propose a third approach: a specific degraded mode that is robust but only used if the tonel pure format is not usable.
For that, I reused a syntax I have seen in the CodeImporter with ! as delimiter.

So, If the format method [ methodBody ] cannot be used because methodBody is not clean, the format method !methodBody! is used, where all ! present in methodBody are escaped (by doubling them, classic Pharo/Smalltalk idiom).
Therefore, methodBody can contain any kind of garbage without breaking the whole file.

Note that there is no loss of functionality, the alternative being a corrupted file

[jecisc]

I updated the PR to go against the new Pharo12 branch.

[jecisc]

I find this interesting. What do you think @estebanlm ? Can we merge?