Fix switch statement issue

[kjw142857]

Fixes #93

[gemini-code-assist]

Code Review

This pull request refactors the switch statement code generation in src/compiler/code-generator.ts by reserving 4-byte placeholders for branch targets and patching them later with full 4-byte signed big-endian offsets. A critical issue was identified in the non-table switch (LOOKUPSWITCH) patching logic, where using caseLabels[k] to retrieve the target label can lead to index misalignment and incorrect branch targets or out-of-bounds errors. It is recommended to use caseLabelMap to look up the correct label for each case value instead.

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[gemini-code-assist]

In a LOOKUPSWITCH (non-table switch), using caseLabels[k] to retrieve the target label is incorrect. caseLabels contains one label per case group (including the default label), whereas caseValues contains one entry per individual case value (excluding the default label). If a case group has multiple labels, or if there is a default label, the indices of caseValues and caseLabels will not align, leading to incorrect branch targets or out-of-bounds errors.

Instead, you should use caseLabelMap to look up the correct label for each case value.

        for (let k = 0; k < caseValues.length; k++) {
          const idx = caseLabelIndex[1 + k]
          const lbl = caseLabelMap.get(caseValues[k]) || defaultLabel
          const off = lbl.offset - positionOffset
          cg.code[idx] = (off >> 24) & 0xff
          cg.code[idx + 1] = (off >> 16) & 0xff
          cg.code[idx + 2] = (off >> 8) & 0xff
          cg.code[idx + 3] = off & 0xff
        }

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	72.27% (-0.23% 🔻)	7408/10250
🔴	Branches	59.15% (-0.03% 🔻)	2480/4193
🟡	Functions	69.04%	1320/1912
🟡	Lines	73.13% (-0.24% 🔻)	6974/9536

Show files with reduced coverage 🔻

St.❔	File	Statements	Branches	Functions	Lines
🟡	... / code-generator.ts	65.74% (-2.53% 🔻)	60.7% (-0.33% 🔻)	65.43%	66.55% (-2.56% 🔻)

Test suite run success

1134 tests passing in 64 suites.

Report generated by 🧪jest coverage report action from 1b8e9a5