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Fix/object assign non table source (#1642)#1710

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Perryvw merged 2 commits into
TypeScriptToLua:masterfrom
RealColdFry:fix/object-assign-non-table-source
Apr 16, 2026
Merged

Fix/object assign non table source (#1642)#1710
Perryvw merged 2 commits into
TypeScriptToLua:masterfrom
RealColdFry:fix/object-assign-non-table-source

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@RealColdFry RealColdFry commented Apr 16, 2026

Fixes #1642

Issue playground link

Minimal repro playground link, copied below:

const obj = { key: 1 };                                                                                                                      
const b = { ...(1 < 0 && obj) };                                                                                                             
console.log(b); // expected: {}

{ ...(cond && obj) } is a common idiom: when cond is falsy, the spread short-circuits to false and JS treats it as a no-op (Object.assign coerces primitives to wrapper objects with no own enumerable properties). TSTL's __TS__ObjectAssign didn't guard against non-table sources, so pairs(false) errored at runtime.

Lualib comp

Old

local function __TS__ObjectAssign(target, ...)
    local sources = {...}
    for i = 1, #sources do
        local source = sources[i]
        for key in pairs(source) do
            target[key] = source[key]
        end
    end
    return target
end

New

local function __TS__ObjectAssign(target, ...)
    local sources = {...}
    for i = 1, #sources do
        local source = sources[i]
        if type(source) == "table" then
            for key in pairs(source) do
                target[key] = source[key]
            end
        end
    end
    return target
end

@RealColdFry
fix Object.assign crashing when source is a non-table value
c8cb103 
`{ ...(cond && obj) }` short-circuits to `false` when `cond` is falsy. JS
treats this as a no-op (Object.assign coerces primitives to wrapper objects
with no own enumerable properties), but `__TS__ObjectAssign` was iterating
every source unconditionally, so `pairs(false)` errored at runtime.

Skip non-table sources, matching the spec for null/undefined/primitive args.
@RealColdFry
refactor __TS__ObjectAssign to emit cleaner Lua
782f831 
Invert the type guard so it nests the spread loop instead of using `continue`,
which lowered to a `repeat ... until true` + `break` dance. Same behavior,
the bundled helper now reads like the hand-written original.
@RealColdFry RealColdFry marked this pull request as ready for review April 16, 2026 12:52
@RealColdFry RealColdFry changed the title Fix/object assign non table source Fix/object assign non table source (#1642) Apr 16, 2026
@Perryvw Perryvw merged commit c3b3a8b into TypeScriptToLua:master Apr 16, 2026
5 checks passed
@RealColdFry RealColdFry deleted the fix/object-assign-non-table-source branch April 22, 2026 01:52
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Successfully merging this pull request may close these issues.

Encountered error with { ...(bCheck && obj) }

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@RealColdFry @Perryvw