Emit safe C# for enum constants in CodeFormatter.Write

[jeremydmiller]

Problem

CodeFormatter.Write renders enum values with the single line:

return value.GetType().FullNameInCode() + "." + value;

That implicitly calls Enum.ToString(). For values that aren't a single defined member — particularly bit-OR'd combinations on non-[Flags] enums such as Npgsql.NpgsqlDbType — ToString returns the underlying integer literal as a string, so we emit uncompilable source like:

parameter0.NpgsqlDbType = NpgsqlTypes.NpgsqlDbType.-2147483629;

Roslyn rejects the generated assembly with CS1001 Identifier expected. This is the root cause of the Marten codegen bug tracked at JasperFx/marten#3702 (a [DuplicateField] on List<T> with DbType = NpgsqlDbType.Array | NpgsqlDbType.Text).

Fix

Replace the single-line implementation with WriteEnum, which handles three cases explicitly:

Case	Output
Single defined member (Numbers.one)	Namespace.Numbers.one (unchanged)
[Flags] combo (Toppings.Cheese | Toppings.Pepperoni)	Type.Cheese | Type.Pepperoni
Undefined value (incl. bit-OR'd non-Flags enums)	((Type)(rawIntegerLiteral))

The [Flags] branch defends against the case where ToString still returns a numeric literal (e.g. an Or'd combination whose bits don't all map to defined members) by checking IsNumericLiteral and falling through to the cast form.

Tests

Three new tests in CodeFormatterTests, including a DirtyFlagless enum that mimics the exact NpgsqlDbType shape (non-[Flags] enum whose callers OR member values together).

Passed!  - Failed: 0, Passed: 9, Total: 9 (CodegenTests, all 3 TFMs)

Downstream verification

With this JasperFx built locally and dropped into the NuGet cache, the Marten reproduction test from #3702 (Bug_PR_3702_list_index_compile_error.can_create_array_duplicate_column_on_a_list_field) passes with no Marten-side changes, superseding the call-site patch that PR proposed. Marten will be bumped to the next JasperFx release in a follow-up PR.

🤖 Generated with Claude Code