Allow setting max print width of IDs via Convex.MAXDIGITS.

Author: riccardomurri

src/Convex.jl

@@ -66,6 +66,23 @@ Controls width of tree printing globally for Convex.jl; defaults to 15. Set via
 """
 const MAXWIDTH= Ref(15)
 
+"""
+    MAXDIGITS
+
+When priting IDs of variables, only show the initial and final digits
+if the full ID has more than double the number of digits specified
+here.  So, with the default setting MAXDIGITS=3, any ID longer than 7
+digits would be shortened; for example, ID `14656210999710729289`
+would be printed as `146…289`.
+
+This setting controls tree printing globally for Convex.jl; defaults to 3.
+
+Set via:
+
+    Convex.MAXDIGITS[] = 3
+"""
+const MAXDIGITS= Ref(3)
+
 ### modeling framework
 include("dcp.jl")
 include("expressions.jl")

src/utilities/show.jl

@@ -16,11 +16,15 @@ julia> Convex.show_id(stdout, x)
 id: 163…906
 ```
 """
-show_id(io::IO, x::Union{AbstractExpr, Constraint}; digits = 3) = print(io, show_id(x; digits=digits))
+show_id(io::IO, x::Union{AbstractExpr, Constraint}; digits = MAXDIGITS[]) = print(io, show_id(x; digits=digits))
 
-function show_id(x::Union{AbstractExpr, Constraint}; digits = 3)
+function show_id(x::Union{AbstractExpr, Constraint}; digits = MAXDIGITS[])
     hash_str = string(x.id_hash)
-    return "id: " * first(hash_str, digits) * "…" * last(hash_str, digits)
+    if length(hash_str) > (2*digits + 1);
+        return "id: " * first(hash_str, digits) * "…" * last(hash_str, digits)
+    else
+        return "id: " * hash_str
+    end
 end
 
 """