[k7d]

Fixes #18.

Locals whose names munge to the same JavaScript identifier (a-b and a_b) weren't renamed apart, so one overwrote the other (CLJS-2461, CLJS-3426). The common case is a snake_case param turned into a kebab-case local:

(defn handler [{:keys [board_id]}]
  (let [board-id (parse-uuid board_id)] ...))   ; board_id became the parsed value

This was a prerequisite for #14: with const/let output each collision becomes a parse error.

Fix

The analyzer decided that one local shadows another by comparing symbols. The new cljs.analyzer/shadowed-local also looks for locals in scope that munge to the same name and sets the new local's :shadow to the one with the longest shadow chain. The compiler's existing shadow renaming then emits a_b__$1, a_b__$2, ... Picking the deepest one matters for (let [a_b 1 a-b 2 a_b 3] ...): any other choice gives the third local the same depth as the second, and they collide again.

It replaces handle-symbol-local where locals are bound: fn params, the fn self-name, let/loop (which also covers destructuring and catch, which binds through a let) and letfn.

letfn bindings had no :info {:shadow ...}, which the compiler reads when it renames, so they were never renamed: even (let [x 1] (letfn [(x [] 2)] ...)) emitted var x twice. They now carry it.

Code with no colliding locals compiles to exactly the same output as before, including classic :advanced output: the compiler tests' output assertions and size ratchet pass unchanged. A name with no _ or $ can't collide with another local, so the analyzer skips the scan for it. Compiling the runtime test suite took no measurably longer (about 10.0s with the fix, 10.3s before).

Tests

cljs.core-test/test-locals-munged-to-the-same-name covers lets in return and expression position, fn params, :keys destructuring, loop/recur, nested lets and closures, letfn, catch and reserved words (let/let$). Seven of its assertions fail on main. test-letfn-shadowing-let covers a letfn shadowing a let local.

• script/test-esm: 0 failures, 0 errors
• compiler tests (-M:closure:compiler.test:compiler.test.run): 0 failures, 0 errors
• runtime :advanced, lite and self-host suites under Node: 0 failures, 0 errors