The following transformations gradually faced by "JsError" have all been
moved up front to "JsError::from_v8_exception()":
- finding the first non-"deno:" source line;
- moving "JsError::script_resource_name" etc. into the first error stack
in case of syntax errors;
- source mapping "JsError::script_resource_name" etc. when wrapping
the error even though the frame locations are source mapped earlier;
- removing "JsError::{script_resource_name,line_number,start_column,end_column}"
entirely in favour of "js_error.frames.get(0)".
We also no longer pass a js-side callback to "core/02_error.js" from cli.
I avoided doing this on previous occasions because the source map lookups
were in an awkward place.
This commit adds new "deno check" subcommand.
Currently it is an alias for "deno cache" with the difference that remote
modules don't emit TS diagnostics by default.
Prints warning for "deno run" subcommand if "--check" flag is not present
and there's no "--no-check" flag. Adds "DENO_FUTURE_CHECK" env
variable that allows to opt into new behavior now.
