From e3b637311419f2c64ef11708b1354b60808aaf62 Mon Sep 17 00:00:00 2001
From: odow <o.dowson@gmail.com>
Date: Thu, 11 Apr 2024 13:56:31 +1200
Subject: [PATCH 1/2] [FileFormats.CBF] read functions as VectorOfVariables if
 possible

---
 src/FileFormats/CBF/read.jl | 30 +++++++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)

diff --git a/src/FileFormats/CBF/read.jl b/src/FileFormats/CBF/read.jl
index afdca96748..aff5987e63 100644
--- a/src/FileFormats/CBF/read.jl
+++ b/src/FileFormats/CBF/read.jl
@@ -302,6 +302,27 @@ function _read_DCOORD(io::IO, data::_CBFReadData)
     return
 end
 
+"""
+    _simplify_f_if_possible(f::MOI.VectorAffineFunction)
+
+This function returns a `MOI.VectorOfVariables` if `f` is trivially equivalent
+to `I * x + 0`. This may often happen when reading constraints that could have
+been written as `x in K`, but were instead written as `I * x + 0 in K`.
+"""
+function _simplify_f_if_possible(f::MOI.VectorAffineFunction)
+    if length(f.terms) != length(f.constants)
+        return f
+    end
+    for (i, term) in enumerate(f.terms)
+        if term.output_index != i ||
+           !isone(term.scalar_term.coefficient) ||
+           !iszero(f.constants[i])
+            return f
+        end
+    end
+    return MOI.VectorOfVariables([t.scalar_term.variable for t in f.terms])
+end
+
 """
     Base.read!(io::IO, model::FileFormats.CBF.Model)
 
@@ -382,7 +403,11 @@ function Base.read!(io::IO, model::Model)
             )
         end
         con_set = _cbf_to_moi_cone(data, cone_str, cone_dim)
-        MOI.add_constraint(model, con_func, con_set)
+        MOI.add_constraint(
+            model,
+            _simplify_f_if_possible(con_func),
+            con_set,
+        )
         row_idx += cone_dim
     end
 
@@ -400,10 +425,9 @@ function Base.read!(io::IO, model::Model)
         )
         MOI.add_constraint(
             model,
-            con_func,
+            _simplify_f_if_possible(con_func),
             MOI.PositiveSemidefiniteConeTriangle(side_dim),
         )
     end
-
     return
 end

From 2e755a8a7d3e91ee305f1babc8b4fc7bfb972754 Mon Sep 17 00:00:00 2001
From: odow <o.dowson@gmail.com>
Date: Thu, 11 Apr 2024 14:04:56 +1200
Subject: [PATCH 2/2] Fix formatting

---
 src/FileFormats/CBF/read.jl | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/src/FileFormats/CBF/read.jl b/src/FileFormats/CBF/read.jl
index aff5987e63..c20026f03e 100644
--- a/src/FileFormats/CBF/read.jl
+++ b/src/FileFormats/CBF/read.jl
@@ -403,11 +403,7 @@ function Base.read!(io::IO, model::Model)
             )
         end
         con_set = _cbf_to_moi_cone(data, cone_str, cone_dim)
-        MOI.add_constraint(
-            model,
-            _simplify_f_if_possible(con_func),
-            con_set,
-        )
+        MOI.add_constraint(model, _simplify_f_if_possible(con_func), con_set)
         row_idx += cone_dim
     end