[FileFormats.LP] fix reading file with variable-coefficient-variable (#2076)

Author: odow

src/FileFormats/LP/LP.jl

@@ -542,7 +542,8 @@ function _get_term(token_types, token_values, offset)
     @assert token_types[offset] == _TOKEN_VARIABLE
     x = MOI.VariableIndex(Int64(token_values[offset]))
     offset += 1
-    if offset > length(token_types) || token_types[offset] == _TOKEN_SIGN
+    if offset > length(token_types) ||
+       token_types[offset] in (_TOKEN_SIGN, _TOKEN_COEFFICIENT)
         return MOI.ScalarAffineTerm(coef, x), offset
     end
     term = if token_types[offset] == _TOKEN_QUADRATIC_DIAG

test/FileFormats/LP/LP.jl

@@ -738,6 +738,21 @@ function test_wrong_way_bounds()
     return
 end
 
+function test_variable_coefficient_variable()
+    io = IOBuffer()
+    write(io, "Minimize\nobj: x -1 y\nEnd")
+    seekstart(io)
+    model = MOI.FileFormats.LP.Model()
+    read!(io, model)
+    out = IOBuffer()
+    write(out, model)
+    seekstart(out)
+    file = read(out, String)
+    @test file ==
+          "minimize\nobj: 1 x - 1 y\nsubject to\nBounds\nx >= 0\ny >= 0\nEnd\n"
+    return
+end
+
 function runtests()
     for name in names(@__MODULE__, all = true)
         if startswith("$(name)", "test_")