fix(transpiler): keep for-loop counters raw in switch-arm return arguments

[yusufcansehirli]

Problem

transpile() can emit invalid JavaScript for a for loop whose counter is reached through the complex-return-argument walker in transformReturnStatement():

for (let iR = 1; 1 <= 3 ? $.get(iR, 0) <= 3 : $.get(iR, 0) >= 3; 1 <= 3 ? $.get(iR, 0)++ : $.get(iR, 0)--) {

$.get(iR, 0)++ is a postfix update on a call expression, which is invalid JavaScript — SyntaxError: Invalid left-hand side expression in postfix operation when the generated function is constructed.

The path is reached when a function's last statement is a bare switch: the implicit return argument is walked by the return-argument transformer, and the default traversal descends into the arm IIFEs and their ForStatement headers.

Repro (12 lines):

//@version=6
indicator("For Counter in Switch Arm")

draw(cond) =>
    float s = 0.0
    switch
        cond =>
            for iR = 1 to 3
                s += iR
        => s

plot(1)

Fix

• Add a ForStatement() {} no-op visitor to the complex return-argument walker so for-headers are never descended into (the loop's declaration/test/update/body are handled by the statement machinery when the enclosing function is transformed).
• Skip loop variables in that walker's Identifier visitor.

Test

tests/transpiler/for-loop-counter-return-argument.test.ts — minimal-repro regression test. Before the fix it fails (generated code contains $.get(iR, 0)++/--); after the fix the counter stays a raw JS local and the generated function constructs and runs.

Verification

• tests/transpiler/ — 33 files / 504 tests pass.
• Full suite: 172 files pass; 2 files (pagination, request-cross-tf) are flaky and also fail intermittently on unpatched main in this environment — unrelated pre-existing flakiness.

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[yusufcansehirli]

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