Most languages are context sensitive.
Most language tools are context free.
How did we go so wrong?
Most language tools are context free.
How did we go so wrong?
Many language tools don't need a full blown language parser and can get by with a context-free parser for the language's superset. Things like autocompletion, spell checking, documentation/highlighting can all be implemented using context-free parsers.
> spell checking ... using context-free parsers
Only up to a point. D's spell checker uses the symbols in scope as its "dictionary". This means it is very good at guessing what you meant instead of what is typed, as the dictionary is very targeted. I.e. it uses the context, and the spell checker is part of the semantic pass.
A[B] C;
That is parsed differently depending on whether B is a constant integer expression in which case it parses to the declaration of an array of type A with a size of B, or whether B is a typename in which case it parses into an hash map with keys of type B and values of type A.
This disambiguation can not be specified by the context free grammar and instead must be delayed until the semantic analysis (which is usually defined by a context sensitive grammar).
Pretty much all statically typed languages work this way with various kinds of ambiguities. In practice, it's not a particularly big deal. But that's kind of my point, there's no need to work exceedingly hard to force a language construct to be context free, especially if making it context free results in a lack of readability or awkward syntax.
It's perfectly fine to specify a superset of the language that is context free, parse an AST for the superset of that language and then resolve AST ambiguities in later phases, such as the semantic analysis phase or the type checking phase. Almost any tool written to assist an IDE with autocompletion or other functionality will have no problem working with the language superset.
It isn't parsed differently. Its semantic meaning depends on what B is, but not the parse.
We never did. We always knew that any real-world useful grammar is multi-level and attribute (well, it's constraint-based, though depending on your definition of "attribute grammar", those are equivalent). That's why we so much like recursive-descent parsers: adding any multi-level constraints are so easy to them - you have a full Turing-complete language at your disposal, unlike simplistic 1-dimensional DSLs of most parser generators.
Context-free grammars are ripe for theoretical computer science work even if they're not practically relevant. On the flipside, I suppose the constraints of context-free grammars are seen as a price not worth paying when designing a language.
Languages that are context-sensitive? C, C++, Java, JavaScript.
Examples of tools based on the starting expectation that languages are context-free? Yacc, Bison, Jay.
Examples of the problems this causes? Well we're using the wrong tool for the job, right from the start. Instead of using an appropriate tool the first thing we do is bend our tools out of shape. We use side-effect actions to subvert the tool's model in an uncontrolled way. We don't get the full benefits of the tool's original model and can't rely on its guarantees.