Emit a wrap expr span_bug only if context is not tainted

[gurry]

Fixes #127332

The ICE occurs because of this span_bug:

rust/compiler/rustc_hir_typeck/src/expr_use_visitor.rs

Lines 732 to 738 in 51917e2

	_ => {
	// the base expression should always evaluate to a
	// struct; however, when EUV is run during typeck, it
	// may not. This will generate an error earlier in typeck,
	// so we can just ignore it.
	span_bug!(with_expr.span, "with expression doesn't evaluate to a struct");
	}

which is triggered by the fact that we're trying to use an enum in a with expression instead of a struct.

The issue originates in commit 814bfe9 from PR #127202. As per the title of that commit the ICEing code should not be reachable any more, but looks like it still is.

This PR changes the code so that the span_bug will be emitted only if the context is not tainted by a previous error.

[rustbot]

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[oli-obk]

r? @oli-obk

Where is the actual error being reported? Can we change something at the error emission site to ensure we don't get here?

[oli-obk]

And... is the type actually an enum or is it an error type by any chance?

[gurry]

r? @oli-obk

Where is the actual error being reported? Can we change something at the error emission site to ensure we don't get here?

The original error which is this:

error[E0436]: functional record update syntax requires a struct
 --> /tmp/icemaker_global_tempdir.kjjtaMiZob00/rustc_testrunner_tmpdir_reporting.bVfRd0uWVozS/mvce.rs:6:22
  |
6 |     Foo::A { x: 6, ..orig };
  |                      ^^^^

is emitted here:

rust/compiler/rustc_hir_typeck/src/expr.rs

Lines 1878 to 1879 in 9e27377

	self.dcx()
	.emit_err(FunctionalRecordUpdateOnNonStruct { span: base_expr.span });

in the function check_expr_struct_fields.

The code path that ICEs starts later in typeck_with_fallback over here:

rust/compiler/rustc_hir_typeck/src/lib.rs

Line 191 in 9e27377

fcx.closure_analyze(body);

The call to analyze_closure eventually invokes ExprUseVisitor which is where the ICE occurs.

Unfortunately, I could not think of a way to cause analyze_closure to skip the ICEing code based on the original error in check_expr_struct_fields.

[gurry]

And... is the type actually an enum or is it an error type by any chance?

It is an enum i.e. the type returned by this call to kind:

rust/compiler/rustc_hir_typeck/src/expr_use_visitor.rs

Line 714 in 9e27377

match self.cx.try_structurally_resolve_type(with_expr.span, with_place.place.ty()).kind() {

is an enum ADT.

[oli-obk]

@bors r+ rollup

Thanks for going through all those hoops for a tiny ICE fix

[bors]

📌 Commit 9da3638 has been approved by oli-obk

It is now in the queue for this repository.

[gurry]

@bors r+ rollup

Thanks for going through all those hoops for a tiny ICE fix

No worries at all 😄