Minifier incorrectly inlines object property with duplicated key from spreaded object

[hyp3rflow]

Describe the bug

Minifier correctly inlines object initialization using spreading operator, however inlining property access from initialized object points to the value from spreaded object even if new property value exists.

Input code

const x = {a: 1};
const y = {...x, a: 2};
console.log(y.a);

Config

{
  "jsc": {
    "parser": {
      "syntax": "ecmascript",
      "jsx": false
    },
    "target": "es2022",
    "loose": false,
    "minify": {
      "compress": {
        "arguments": false,
        "arrows": true,
        "booleans": true,
        "booleans_as_integers": false,
        "collapse_vars": true,
        "comparisons": true,
        "computed_props": true,
        "conditionals": true,
        "dead_code": true,
        "directives": true,
        "drop_console": false,
        "drop_debugger": true,
        "evaluate": true,
        "expression": false,
        "hoist_funs": false,
        "hoist_props": true,
        "hoist_vars": false,
        "if_return": true,
        "join_vars": true,
        "keep_classnames": false,
        "keep_fargs": true,
        "keep_fnames": false,
        "keep_infinity": false,
        "loops": true,
        "negate_iife": true,
        "properties": true,
        "reduce_funcs": false,
        "reduce_vars": false,
        "side_effects": true,
        "switches": true,
        "typeofs": true,
        "unsafe": false,
        "unsafe_arrows": false,
        "unsafe_comps": false,
        "unsafe_Function": false,
        "unsafe_math": false,
        "unsafe_symbols": false,
        "unsafe_methods": false,
        "unsafe_proto": false,
        "unsafe_regexp": false,
        "unsafe_undefined": false,
        "unused": true,
        "const_to_let": true,
        "pristine_globals": true
      },
      "mangle": false
    }
  },
  "module": {
    "type": "es6"
  },
  "minify": false,
  "isModule": true
}

Playground link (or link to the minimal reproduction)

https://play.swc.rs/?version=1.7.18&code=H4sIAAAAAAAAA0vOzysuUahQsFWoTrRSMKy15koGi1SCRPT09Cp0FIDiRlDx%2FJxUvZz8dI1KvURNawA8alvVOwAAAA%3D%3D&config=H4sIAAAAAAAAA32UO3LjMAyG%2B5zCozrFjostcoDtcgYOTYIyvXxoCNCxJuO7L0TJj40hdRI%2B%2FAAJgPh%2B2%2B26E5ruY%2FfNn%2Fwz6IJQ7v9swTGRvrClAxM1muIH6t5v9IQTcjogNNN1Jh3p0gM1Fe5%2F7feLogs5I9wUiy365N34nNPkOBRAfLKxlUPWCInwf%2F3CSv6aAJX6bD%2FkHECnDaI0Kp8IeihSYJND0AOCOusiRJlOqovHLKWYYCWwaih5EHmynnxOnPOVWtBWmWxBQL6AIX8GSca5WJaQryfcp2ELh9r3rc8%2F1HDWoWoScsKltYRPK0Q9Zo%2BkXE1SCWe4UoMZLsX9qfROFaBa0qvulH1a6clfAK5A0IhJR5DiNg%2FH87SmdptKnxyPLI0C5%2FmWbpmg56Iq751Q2akyUMhL3Sxgq4GpskY6zoJXyofeggLneFaE0PjlyRylpDQOkJ0AuL%2FaSVM1A3V%2FhSt8ehAb%2BA%2FfkuQBWzyipuM6xTEecthIEIGO2W44cCsor%2BPCW%2BIyrPOaLPBogBVdKjbwugT4AVBWoe3Ll9ng58ERVR%2Fy4bEmFofrfQ9HnfrHe59X8dvi0MVsa4PLkp%2F6O6%2Fm393D6baF7wfvPH7elC3p9R%2BoYzQdMAYAAA%3D%3D

SWC Info output

No response

Expected behavior

y.a should be evaluated as 2 from y's initialization.

Actual behavior

No response

Version

1.7.18

Additional context

No response

[kdy1]

Investigation

The sequences pass does not stop on spread properties.

  TRACE  sequences: Trying to merge `y#2 = {
    ...{
        a: 1
    },
    a: 2
}` => `y#2`
    at crates/swc_ecma_minifier/src/compress/optimize/sequences.rs:2046
    in merge_sequential_expr with a: "y#2 = {\n    ...{\n        a: 1\n    },\n    a: 2\n}", b: "y#2"
    in merge_sequential_expr with a: "y#2 = {\n    ...{\n        a: 1\n    },\n    a: 2\n}", b: "y#2.a"
    in merge_sequential_expr with a: "y#2 = {\n    ...{\n        a: 1\n    },\n    a: 2\n}", b: "console#1.log(y#2.a)"
    in merge_sequences_in_exprs with len: 3
    in merge_sequences_in_stmts with items_len: [0, 3]
    in merge_sequences_in_stmts
    in handle_stmt_likes
    in visit_mut_module_items
    in apply full optimizer
    in optimize with pass: 1
    in compress ast
    in minify
    in compress-only

  DEBUG  sequences: Inlining sequential expressions (`y#2`), kind: "change"
    at crates/swc_ecma_minifier/src/compress/optimize/sequences.rs:2539
    in merge_sequential_expr with a: "y#2 = {\n    ...{\n        a: 1\n    },\n    a: 2\n}", b: "y#2"
    in merge_sequential_expr with a: "y#2 = {\n    ...{\n        a: 1\n    },\n    a: 2\n}", b: "y#2.a"
    in merge_sequential_expr with a: "y#2 = {\n    ...{\n        a: 1\n    },\n    a: 2\n}", b: "console#1.log(y#2.a)"
    in merge_sequences_in_exprs with len: 3
    in merge_sequences_in_stmts with items_len: [0, 3]
    in merge_sequences_in_stmts
    in handle_stmt_likes
    in visit_mut_module_items
    in apply full optimizer
    in optimize with pass: 1
    in compress ast
    in minify
    in compress-only

  DEBUG  sequences: Dropping inlined variable, kind: "change"
    at crates/swc_ecma_minifier/src/compress/optimize/sequences.rs:2399
    in merge_sequential_expr with a: "y#2 = {\n    ...{\n        a: 1\n    },\n    a: 2\n}", b: "y#2"
    in merge_sequential_expr with a: "y#2 = {\n    ...{\n        a: 1\n    },\n    a: 2\n}", b: "y#2.a"
    in merge_sequential_expr with a: "y#2 = {\n    ...{\n        a: 1\n    },\n    a: 2\n}", b: "console#1.log(y#2.a)"
    in merge_sequences_in_exprs with len: 3
    in merge_sequences_in_stmts with items_len: [0, 3]
    in merge_sequences_in_stmts
    in handle_stmt_likes
    in visit_mut_module_items
    in apply full optimizer
    in optimize with pass: 1
    in compress ast
    in minify
    in compress-only

[kdy1]

Well, investigation was wrong.

console.log({
    ...{
        a: 1
    },
    a: 2
}.a);

becomes

console.log(1);

So the cause is expr_simplifier

[swc-bot]

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.