Fix SPARSE before MASKED WITH column ordering (#216)

[NAVEEN NAIK (ZEUSXXIV)]

Description

Fixes #216

CREATE TABLE column definitions that combine SPARSE and MASKED WITH in the order documented by the CREATE TABLE reference (SPARSE first, then MASKED WITH) failed to parse with "Incorrect syntax near 'MASKED'", even though the reversed order (MASKED WITH … SPARSE) parsed fine and both are accepted by the SQL Server engine.

Failing before this change (documented order):

CREATE TABLE t (c VARCHAR(100) SPARSE MASKED WITH (FUNCTION = 'default()') NULL);

Worked before (reversed order):

CREATE TABLE t (c VARCHAR(100) MASKED WITH (FUNCTION = 'default()') SPARSE NULL);

Root cause

In the regularColumnBody grammar rule, the maskedClause was only accepted before the SPARSE/FILESTREAM/COLUMN_SET storage options. There was no way for MASKED WITH to follow SPARSE, so the documented ordering produced a parse error.

Fix

The regularColumnBody rule now accepts maskedClause in two positions:

1. The pre-existing leading maskedClause (before the storage options) — handles MASKED WITH … SPARSE (reversed order).
2. A new maskedClause after the storage-options block, before the HIDDEN clause where present — handles SPARSE … MASKED WITH (documented order).

The trailing occurrence is guarded by {NextTokenMatches(Masked) && !vParent.IsMasked}?, which reuses the existing IDataMaskingSetter.IsMasked state so that MASKED WITH cannot be specified twice on the same column (the guard makes the second position inert once the leading one has already consumed a MASKED WITH).

Applied to every grammar that supports MASKED WITH (a SQL Server 2016 feature): TSql130 through TSql180 and TSqlFabricDW.

Compatibility / non-breaking

This change is intentionally additive and does not alter the public API surface:

• No Ast.xml changes — no AST class, enum, or property was added, renamed, or retyped. It reuses the existing IDataMaskingSetter.IsMasked / MaskingFunction and ColumnStorageOptions members.
• No behavioral regression — the new clause only triggers on a MASKED token that previously produced a parse error, so no previously valid input changes its AST or output. All existing baselines are unchanged.
• The script generator already emits SPARSE MASKED WITH …, so parse → generate → re-parse round-trips cleanly for both input orders.

Tests

• Positive round-trip: Test/SqlDom/TestScripts/SparseMaskedColumnOrderTests130.sql with baseline Test/SqlDom/Baselines130/SparseMaskedColumnOrderTests130.sql, wired through Only130SyntaxTests.cs. Covers the exact statement from the issue (documented order), the reversed order, and SPARSE FILESTREAM + MASKED WITH. Verified across the TSql130–TSql180 parsers.
• Negative / version-gating: SparseMaskedColumnNegativeTest in ParserErrorsTests.cs asserts that specifying MASKED WITH twice on one column is a parse error (SQL46010).
• Full suite passes on both target frameworks: net8.0 — 907/907, net472 — 907/907.

Code Changes

• Unit tests are added, if possible
• Existing tests are passing
• New or updated code follows the guidelines here