Fix anon const def-creation when macros are involved take 2

[BoxyUwU]

Fixes #130321

There were two cases that #129137 did not handle correctly:

• Given a const argument Foo<{ bar!() }> in which bar!() expands to N, we would visit the anon const and then visit the { bar() } expression instead of visiting the macro call. This meant that we would build a def for the anon const as { bar!() } is not a trivial const argument as bar!() is not a path.
• Given a const argument Foo<{ bar!() }> is which bar!() expands to { qux!() } in which qux!() expands to N, it should not be considered a trivial const argument as {{ N }} has two pairs of braces. If we only looked at qux's expansion it would look like a trivial const argument even though it is not. We have to track whether we have "unwrapped" a brace already when recursing into the expansions of bar/qux/any macro

r? @camelid

[BoxyUwU]

This change to call visit_macro_invoc instead of walk_anon_const is what fixes #130321. Everything else in this PR is changes made to track if we've already unwrapped a brace or not (and related code deduplication since it would be pretty messy otherwise)

[camelid]

Wondering if it would be clearer to return Option<&Expr> (also matching the function's name)? Then it could be used as expr.maybe_unwrap_block().unwrap_or(expr) e.g. Maybe that'd be worse, but it just came to mind.

[BoxyUwU]

Yeah I think this is probably just worse for every caller unfortunately because this is not the nicest name/signature combo 😅

[camelid]

r=me with these comments addressed. Thanks!

[BoxyUwU]

@bors r=camelid rollup=never

[bors]

📌 Commit 781ec11 has been approved by camelid

It is now in the queue for this repository.

[bors]

⌛ Testing commit 781ec11 with merge 55043f0...

[bors]

☀️ Test successful - checks-actions
Approved by: camelid
Pushing 55043f0 to master...

[rust-timer]

Finished benchmarking commit (55043f0): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -0.7%, secondary -1.7%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.4%, 0.4%]	1
Regressions ❌ (secondary)	3.7%	[3.7%, 3.7%]	1
Improvements ✅ (primary)	-1.8%	[-1.8%, -1.8%]	1
Improvements ✅ (secondary)	-4.4%	[-5.2%, -3.5%]	2
All ❌✅ (primary)	-0.7%	[-1.8%, 0.4%]	2

Cycles

Results (primary 0.7%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.7%	[0.7%, 0.7%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.7%	[0.7%, 0.7%]	1

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 769.615s -> 769.437s (-0.02%)
Artifact size: 341.55 MiB -> 341.48 MiB (-0.02%)