Clean up resolve error reporting #7379
Description
Currently, resolve does a lot of redundant error reporting. For example,
/home/cmr/hacking/rust/src/libextra/interner.rs:161:8: 161:18 error: unresolved name
/home/cmr/hacking/rust/src/libextra/interner.rs:161 ast::ident { repr: off, ctxt: 0 }
^~~~~~~~~~
/home/cmr/hacking/rust/src/libextra/interner.rs:161:8: 161:18 error: use of undeclared module `ast`
/home/cmr/hacking/rust/src/libextra/interner.rs:161 ast::ident { repr: off, ctxt: 0 }
^~~~~~~~~~
/home/cmr/hacking/rust/src/libextra/interner.rs:161:8: 161:18 error: `ast::ident` does not name a structure
/home/cmr/hacking/rust/src/libextra/interner.rs:161 ast::ident { repr: off, ctxt: 0 }
^~~~~~~~~~
This should be a single error, "error: use of undeclared module ast".
Another example:
/home/cmr/hacking/rust/src/libextra/interner.rs:161:8: 161:18 error: unresolved name
/home/cmr/hacking/rust/src/libextra/interner.rs:161 ast::ident { repr: off, ctxt: 0 }
^~~~~~~~~~
/home/cmr/hacking/rust/src/libextra/interner.rs:161:8: 161:18 error: use of undeclared module `ast`
/home/cmr/hacking/rust/src/libextra/interner.rs:161 ast::ident { repr: off, ctxt: 0 }
^~~~~~~~~~
/home/cmr/hacking/rust/src/libextra/interner.rs:161:8: 161:18 error: `ast::ident` does not name a structure
/home/cmr/hacking/rust/src/libextra/interner.rs:161 ast::ident { repr: off, ctxt: 0 }
^~~~~~~~~~
Fixing this will require careful finagling of resolve. The best way to handle this is probably some central error reporting infrastructure, and as soon as one error is reported, stop making new errors for the current span. This is going to be tricky because every error path needs to be followed to ensure that an error is reported, and that if only one error is reported, it is the right error. Needs vastly improved test coverage in compile-fail. Shouldn't be hard, but will take time.
Nominating for production-ready.