Use track_errors instead of hand-rolling such a check

Const eval asserts that reporting an error for statics actually worked. This is not only done in a wrong way (checks for no error having happened in the entire compilation), it's also very fragile. We should instead use the track_errors method around the report_as_error call, and in case track_errors returns Ok, we need to do the delay_span_bug.

The relevant code that needs to be changed can be found in

rust/src/librustc_mir/const_eval.rs

Lines 645 to 654 in 16e7e05

    
           let reported_err = err.report_as_error(ecx.tcx, 
        
                                                  "could not evaluate static initializer"); 
        
           // Ensure that if the above error was either `TooGeneric` or `Reported` 
        
           // an error must be reported. 
        
           if tcx.sess.err_count() == 0 { 
        
               tcx.sess.delay_span_bug(err.span, 
        
                                       &format!("static eval failure did not emit an error: {:#?}", 
        
                                                reported_err)); 
        
           } 
        
           reported_err

Wouldn't using track_errors cause the compiler to stop at const evaluation? Ideally we would want the compiler to choose a reasonable recovery value (just a binding of TyErr?) and continue to minimize the loop of "fix 5 errors, get 300 errors" (#39275).

track_errors doesn't actually stop anything. It just gives you a Result::Err if new errors occured and a Result::Ok otherwise.

@oli-obk

@oli-obk I want to solve this, could I open a PR(and ask you to review)?

Jup! It's all yours!

Rollup merge of rust-lang#59358 - JohnTitor:use-track-errors, r=oli-obk

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Use `track_errors` instead of hand-rolling such a check #59215

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	let reported_err = err.report_as_error(ecx.tcx,
	"could not evaluate static initializer");
	// Ensure that if the above error was either `TooGeneric` or `Reported`
	// an error must be reported.
	if tcx.sess.err_count() == 0 {
	tcx.sess.delay_span_bug(err.span,
	&format!("static eval failure did not emit an error: {:#?}",
	reported_err));
	}
	reported_err

Use track_errors instead of hand-rolling such a check #59215

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estebank commented on Mar 15, 2019

oli-obk commented on Mar 15, 2019

JohnTitor commented on Mar 21, 2019

oli-obk commented on Mar 22, 2019

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Use `track_errors` instead of hand-rolling such a check #59215