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Built-in length expressions can keep the operand type. Infer integer for
strings and tables, including aliases and unions. Preserve custom length
operators and the existing fallback for invalid or unresolved operands.
Narrow a[#a] to the element type after a nonempty guard on every path:
---@type string[]
local a = {'first'}
if not a[1] then return end
local last = a[#a] -- string
Limit the proof to direct local tables with no writes, aliases, captures
or escapes anywhere in the function. Check all references once and reuse
the existing flow graph to keep the proof independent of call effects.
Correct constant-index inference so upper bounds keep nil:
if #a <= 1 then local first = a[1] end -- string|nil
Keep equality as a lower-bound proof and handle reversed comparisons.
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Infer
integerfor built-in string and table lengths through aliases and unions. Preserve customlenoperators and the existing fallback for invalid or unresolved operands.Allow a nonempty guard to prove that
a[#a]has the array's element type:Limit this proof to direct local table literals with no writes, aliases, captures, or escapes anywhere in the function. A guard must hold on every incoming path.
Correct existing constant-index inference so an upper bound alone does not prove an element exists:
Keep equality as a lower-bound proof and handle reversed length comparisons under the same rules.
Related to #886.