[philipaxer]

Part 2 of the series for #952, which replaces name-string scoping in generate blocks with a scope tree and a binder. No behaviour change.

Depends on #962: until that merges, this branch also shows its commits. New here:

• ae24b8dc Register XEZIM_BIND_AUDIT and initialize the identifier binding (§23.9)
• 6380eafa Test the bind audit's output and that it changes no artifact byte (§23.9)
• b2ed1df0 Sync core revision

Core side: aionhw/xezim-core#172 (pinned at 420f850; the last commit, "Sync core revision", sets the pin).

Changes:

• bound is initialized at each identifier the simulator builds.
• XEZIM_BIND_AUDIT is in the env var registry.

Tests: tests/hierarchy/bind_audit.rs: audit output, and no artifact byte changes.

The audit results, memory cost and what is not covered are in the core PR.

Tests after the rebase onto main

Rebased onto core 5b0b02e and xezim 2e4e7f99. The results above were measured before the rebase, against the previous PR of the series.

• core cargo test: 443 passed, 0 failed.
• xezim cargo test --release --test hierarchy (built without LTO): 784 passed, 0 failed.
• The full suites ran on part 7 of the series: xezim 6457 passed, 0 failed, 1 ignored (main: 6332, 0, 1). CI runs them on this PR.

The series

This PR is one part of a stacked series for #952. This section is the same in every part, so each PR can be read on its own.

Problem. A generate block is a scope (§23.9, §27.5, §27.6), but xezim resolved names in generate blocks by string. The elaborator renamed declarations textually (f → g.f) from per-block name lists, and the simulator retried a missed name by its last segment at run time. Each fix to that scheme, including the one for #897, broke other legal programs: a local hiding a block function was renamed anyway, items outside the copied list kept the bare name, two unlabelled blocks with the same variable collided, a child instance's call reached the wrong parent, and disable g.t matched by leaf.

Approach.

• Core builds a scope tree for each definition: its generate blocks, all arms included, each with its declarations (scope_tree.rs).
• A binder resolves every simple name against that tree and writes the result on the identifier: a declaration, a local or other hiding name, or "upward" (§23.8.1) (elaborate/bind.rs).
• The generate rename then follows the binding instead of name lists. The names it produces (g.f, u.g[1].x, genblk2.t) are the keys the runtime already uses, so xezim needs almost no source change.
• XEZIM_BIND_AUDIT=1 prints each binding next to what the rename did, so every disagreement can be listed.

Parts (core / xezim; each depends on the one before and repeats its commits until that merges):

Part	Core	xezim	What it does
1	aionhw/xezim-core#171	#962	Scope tree; generate scope names (genblk<n>, §27.6 zero padding, §27.5 direct nesting) come from it
2	aionhw/xezim-core#172	#963	Binder and audit; no behaviour change
3	aionhw/xezim-core#173	#964	The rename follows the binding: a name a local, formal, class member or import hides keeps its spelling
4	aionhw/xezim-core#174	#965	The rename reaches final blocks, classes, gates, properties, sequences, let, covergroups, clocking and constraints
5	aionhw/xezim-core#175	#966	Bare upward calls from child instances resolve through the instance tree (§23.8.1)
6	aionhw/xezim-core#176	#967	disable by path and by label is bound like other names (§9.6.2)
7	aionhw/xezim-core#177	#968	Data of unlabelled generate blocks is scoped under genblk<n>
8	aionhw/xezim-core#180	#971	Data is renamed by binding at every position; the upward search continues past a variable
9	aionhw/xezim-core#181	#974	Typedefs of a block take the block's key
10	aionhw/xezim-core#182	#975	The binder covers the remaining legal bare names; no output change
11	aionhw/xezim-core#183	#981	Undeclared names are reported by binding: a bare name in an instance that nothing declares is an error, where it read a value found by its last segment
12	aionhw/xezim-core#184	#989	The generate rename takes its spelling from the binding; the name maps, the rename gate and the audit's comparison are removed (core -1,020/+454)
13	aionhw/xezim-core#185	#990	One generate walker instead of two; genvars are also substituted in properties, sequences, covergroups, gates and formal defaults of a loop (§27.4) (core -347/+101)

Independent of the series: #969 (time scope and clocking of a block in an instance) and #970 (a subroutine with no written lifetime stays static on the compiled tier).

Still to come.

• Held until there is feedback: duplicate-declaration diagnostics.
• Not planned: keys for classes in generate blocks. A class in a generate loop stays one class.

The run-time retries by leaf name stay. They serve shapes the binder cannot decide before the run (a class method calling its instance's task, g[k].f() with a variable index, virtual interfaces) and name resolution outside generate blocks (interface ports, $root, packages).

Size so far (parts 1 to 13 against main): core +4,476/-1,066 outside tests (net +3,410), +2,458 tests; xezim +198/-101 outside tests, mostly the core pin, +3,550 tests.

Testing. Every part passed the full xezim suite and the core suite before the rebase onto main. After the rebase, part 7 passed the full suites on main, and parts 8 to 13 passed the hierarchy and core suites. CI runs the rest. Each part's audit and artifact identity against the previous part are in its own text. Expected values come from IEEE 1800-2023 and are checked against Verilator 5.055 where it accepts the program.

Review order. Parts 1 and 2 are the base; the rest read from them. Reviewing those two first settles the direction.

[aionhw]

Integrated by cherry-pick with @philipaxer's authorship preserved, as the whole series: xezim-core 38f31c3…d802056 (core #171–#183) and xezim 163df958…554812e6 (#962–#981). Each layer has a code commit and a test commit, with #952 in the subjects. The per-layer "Sync core revision" commits were replaced by one sync to the final core revision.

Follow-ups for gaps found in review, each checked against the reference simulator:

• VPI reads of an unlabelled generate block's variables (top.genblk1.x) read the block's value again: 1b5b8584, ddddd148.
• disable g1.blk and disable r[0].w stop the named block, matched by full path, not one with the same label elsewhere: 2c0d0298, 786612c5.
• A typedef that depends on the genvar of a generate-for inside an instance has each iteration's width: 6cb836c, e159ff0c.
• $unit::x in a generate block that declares x reads the unit's x: 3ca0d09, 181e269b, 629050a8.
• Implicit nets used in a generate block belong to that block, one per iteration, and g[0].n reaches them: df52996, 0f0c6ef, 38a8498c.
• The binder's hidden-name search is indexed by name. It was a linear scan per name, quadratic in one scope's locals: 2a80522, a1e7912.

Two cases are left: a disable path naming a nested block (still matched by label), and classes declared in generate loops.

Published in xezim 603c9bf3 with xezim-core 212dde0.
Validation: the full xezim suite passes (6610 tests, 0 failed, 1 ignored), with xezim-core 514 and parser 233 tests, the JIT smoke and DPI fallback tests, and a 1.92 MSRV check.