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[FileFormats.LP] Fix reading empty constraint #3088

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Merged
odow merged 1 commit into from
Sep 16, 2026
+29 −2
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[FileFormats.LP] Fix reading empty constraint #3088

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13 changes: 11 additions & 2 deletions src/FileFormats/LP/read.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -1109,17 +1109,26 @@ function _parse_constraint_indicator(
)
end

function _is_empty_constraint(state::_LexerState)
return _next_token_is(state, _TOKEN_GREATER_THAN) ||
_next_token_is(state, _TOKEN_LESS_THAN) ||
_next_token_is(state, _TOKEN_EQUAL_TO)
end

# <constraint> :==
# <name> <expression> <set-suffix>
# <name> [<expression>] <set-suffix>
# | <name> <constraint-sos>
# | <name> <constraint-indicator>
function _parse_constraint(state::_LexerState, cache::_ReadCache)
function _parse_constraint(state::_LexerState, cache::_ReadCache{T}) where {T}
name = _parse_name(state, cache)
# Check if this is an SOS constraint
c = if _is_sos_constraint(state)
_parse_constraint_sos(state, cache)
elseif _is_indicator_constraint(state)
_parse_constraint_indicator(state, cache)
elseif _is_empty_constraint(state)
set = _parse_set_suffix(state, cache)::MOI.AbstractScalarSet
MOI.add_constraint(cache.model, zero(MOI.ScalarAffineFunction{T}), set)
else
f = _parse_expression(state, cache)
# The type annotation is needed for JET.
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18 changes: 18 additions & 0 deletions test/FileFormats/LP/test_LP.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -1873,6 +1873,24 @@ function test_empty_function()
return
end

function test_read_empty_constraint()
model = MOI.FileFormats.LP.Model{Float64}()
read!(IOBuffer("min\nst\n>= 0\nend"), model)
target = MOI.FileFormats.LP.Model{Float64}()
f = zero(MOI.ScalarAffineFunction{Float64})
MOI.add_constraint(target, f, MOI.GreaterThan(0.0))
@test sprint(print, model) == sprint(print, target)
# With name
model = MOI.FileFormats.LP.Model{Float64}()
read!(IOBuffer("min\nst\nc: == 2\nend"), model)
target = MOI.FileFormats.LP.Model{Float64}()
f = zero(MOI.ScalarAffineFunction{Float64})
c = MOI.add_constraint(target, f, MOI.EqualTo(2.0))
MOI.set(target, MOI.ConstraintName(), c, "c")
@test sprint(print, model) == sprint(print, target)
return
end

end # module

TestLP.runtests()
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