Support the MySQL spatial types, SRID attribute, SPATIAL constraint, and CHAR/VARCHAR attributes

[kyleconroy]

Closes the remaining data-type gaps found by auditing the MySQL 26.7 reference manual's data-type chapter (§13) against parseType. All of this syntax postdates the goyacc grammar (TiDB never supported spatial data), so the grammar is written from the reference manual, following the precedent of the statement-coverage PRs (#38–#41).

Spatial types (§13.4.1)

• The eight spatial column data types: GEOMETRY, POINT, LINESTRING, POLYGON, MULTIPOINT, MULTILINESTRING, MULTIPOLYGON, and GEOMETRYCOLLECTION, with GEOMCOLLECTION lexing as its GEOMETRYCOLLECTION synonym via the aliases table (the DEC → DECIMAL precedent).
• MySQL reports every spatial column as type byte 0xff on the wire, so the subtypes get parser-only type bytes 0xe2–0xe8 following the TypeTiDBVectorFloat32 precedent; spatial FieldTypes carry the binary charset, like JSON. This keeps POINT round-tripping as POINT instead of collapsing to GEOMETRY.
• The SRID n column attribute (§13.1.20.10): new ColumnOptionSrid, with the value in a new ColumnOption.UintValue field.
• The SPATIAL [INDEX | KEY] table constraint (§15.1.20) in CREATE TABLE and ALTER TABLE ... ADD, mirroring the FULLTEXT alternative with a new ConstraintSpatial (CREATE SPATIAL INDEX already parsed).
• CAST/CONVERT to the spatial types (§14.10, castable since MySQL 8.0.24), with RestoreAsCastType coverage.

CHAR/VARCHAR attributes (§13.3.1)

The audit found no missing type names beyond spatial, but three missing attribute spellings: CHAR(5) BYTE (the documented alias for BINARY(5)), VARCHAR(10) ASCII, and VARCHAR(10) UNICODE. The goyacc grammar allowed the ASCII/UNICODE/BYTE attributes only on TEXT/ENUM/SET/LONG; MySQL gives CHAR and VARCHAR the same attribute set. parseCharTail/parseVarcharTail now parse OptCharsetWithOptBinary — a superset whose default alternative is OptBinary, so every previously accepted spelling parses identically — and normalize the binary charset to BinaryFlag plus the binary collation, mirroring the TextType action, so CHAR(5) BYTE produces the same FieldType as parsing its BINARY(5) restore output.

UNICODE keeps the historical goyacc semantics: it maps to the unsupported ucs2 charset and fails with the same Unknown character set: 'ucs2' action error TEXT UNICODE has always produced; the goldens record that error contract.

Bookkeeping

• Keyword tables: GEOMETRY, GEOMETRYCOLLECTION, LINESTRING, MULTILINESTRING, MULTIPOINT, MULTIPOLYGON, POLYGON, and SRID become unreserved keywords, matching their MySQL 26.7 classification (POINT already was); TestKeywordsLength counts updated accordingly.
• The ast and types changes are backwards-compatible: appended enum values, a new ColumnOption field, and new type-byte map entries. testdata/errors.json is unaffected.
• New spatial_types file-driven test group covers the types, SRID, the constraint forms, casts, and the new keywords in identifier position; compat_types gains the CHAR/VARCHAR attribute cases.

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https://claude.ai/code/session_01C3dMfdpMyaWffPoh8RBia4

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