fix: fix stack overflow when converting Term to non-concrete coefficient type (#332)

* fix: fix stack overflow when `convert`ing `Term` to non-concrete coefficient type

* fix: fix conversion to identically typed `Term`

Author: AayushSabharwal

src/default_term.jl

@@ -31,6 +31,13 @@ monomial_type(::Type{<:Term{C,M}}) where {C,M} = M
 function Base.convert(::Type{Term{T,M}}, m::AbstractMonomialLike) where {T,M}
     return Term(one(T), convert(M, m))
 end
+function Base.convert(::Type{Term{T,M}}, t::AbstractTerm) where {T,M}
+    return Term{T,M}(convert(T, coefficient(t)), convert(M, monomial(t)))
+end
+function Base.convert(::Type{Term{T,M}}, t::Term{T,M}) where {T,M}
+    return t
+end
+
 function convert_constant(::Type{Term{C,M} where C}, α) where {M}
     return convert(Term{typeof(α),M}, α)
 end

test/commutative/term.jl

@@ -63,6 +63,10 @@ MP.term_type(::Type{Term2{T,M}}) where {T,M} = MP.Term{T,M}
     @test_throws InexactError push!([1], 2x)
     @test_throws InexactError push!([x^2], 2x)
 
+    t = MP.term(1, x)
+    @test convert(MP.Term{Number,MP.monomial_type(t)}, t) isa
+          MP.Term{Number,MP.monomial_type(t)}
+
     @testset "Effective variables" begin
         T = variable_union_type(x)
         @test x isa T