[FileFormats.LP] fix new lines in middle of quadratic objective (#2184)

Author: odow

src/FileFormats/LP/LP.jl

@@ -956,6 +956,9 @@ function Base.read!(io::IO, model::Model)
             _set_objective_sense(section, model, lower_line)
             continue
         end
+        while _line_continues(section, peeked_line)
+            line, peeked_line = _readline(io, string(line, ' ', peeked_line))
+        end
         _parse_section(section, model, cache, line)
     end
     obj = if isempty(cache.quad_obj_terms)
@@ -971,18 +974,32 @@ function Base.read!(io::IO, model::Model)
     return
 end
 
+function _line_continues(
+    ::Union{typeof(_KW_OBJECTIVE),typeof(_KW_CONSTRAINTS)},
+    peeked_line::AbstractString,
+)
+    return any(Base.Fix1(startswith, peeked_line), ('+', '-'))
+end
+
+_line_continues(::Any, ::Any) = false
+
 function _readline(io::IO, line::AbstractString)
     if eof(io)
         return line, nothing
     end
     peeked_line = _strip_comment(string(readline(io)))
     if isempty(line)
+        # If the line is empty, go to the next
         return _readline(io, peeked_line)
     elseif isempty(peeked_line)
+        # If the peeked line is empty, get another
         return _readline(io, line)
-    elseif any(c -> endswith(line, c), ('+', '-', '[', '='))
+    elseif any(Base.Fix1(endswith, line), ('+', '-', '[', '='))
+        # If the line ends with a continuation character, read in the next line.
         return _readline(io, string(line, ' ', peeked_line))
-    elseif startswith(peeked_line, ']') || startswith(peeked_line, '/')
+    elseif any(Base.Fix1(startswith, peeked_line), (']', '/'))
+        # Always read in the next line if it starts with ] or /, which are used
+        # in quadratic functions.
         return _readline(io, string(line, ' ', peeked_line))
     end
     return line, peeked_line

test/FileFormats/LP/LP.jl

@@ -884,6 +884,61 @@ function test_read_quadratic()
         "1 x + 1 y + [ 2 x * y + 2 y ^ 2 ]",
         "1 x + 1 y + [ 4 x * y + 4 y ^ 2 ]/2",
     )
+    _test_read_quadratic(
+        "[ 1.0 x^2 \n+ 1.0 x * y\n+ 1.0 y * y ]/2",
+        "[ 1 x ^ 2 + 1 x * y + 1 y ^ 2 ]/2",
+    )
+    _test_read_quadratic(
+        "[ 1.0 x^2 \n- 1.0 x * y\n+ 1.0 y * y ]/2",
+        "[ 1 x ^ 2 - 1 x * y + 1 y ^ 2 ]/2",
+    )
+    _test_read_quadratic(
+        "[ 1.0 x^2 -\n 1.0 x * y +\n1.0 y * y ]/2",
+        "[ 1 x ^ 2 - 1 x * y + 1 y ^ 2 ]/2",
+    )
+    _test_read_quadratic(
+        "[ 1.0 x^2 + 1.0 x * y\n+ 1.0 y * y ]/2",
+        "[ 1 x ^ 2 + 1 x * y + 1 y ^ 2 ]/2",
+    )
+    return
+end
+
+function test_read_newline_breaks()
+    io = IOBuffer()
+    input_text = """
+    minimize
+    obj: 1 x + 2 y
+        + 3 z
+    subject to
+    c: x -
+    y
+    + z ==
+    0
+    Bounds
+    x >= 0
+    -1 <= y
+    +1 <= z <= +2
+    End
+    """
+    write(io, input_text)
+    model = MOI.FileFormats.LP.Model()
+    seekstart(io)
+    read!(io, model)
+    out = IOBuffer()
+    write(out, model)
+    seekstart(out)
+    output_text = """
+    minimize
+    obj: 1 x + 2 y + 3 z
+    subject to
+    c: 1 x - 1 y + 1 z = 0
+    Bounds
+    x >= 0
+    y >= -1
+    1 <= z <= 2
+    End
+    """
+    @test read(out, String) == output_text
     return
 end