fix(diff): default missing VARCHAR length for MySQL-family targets

crates/dbx-core/src/sql_dialect/ddl_profile.rs

@@ -103,6 +103,11 @@ pub struct DdlDialectProfile {
     pub auto_inc: AutoIncSyntax,
     /// When false, display widths like `INT(11)` are stripped if no type_map hit.
     pub supports_display_width: bool,
+    /// Whether this target's VARCHAR/CHARACTER VARYING/NVARCHAR syntax rejects a
+    /// missing length (e.g. `VARCHAR` with no length is a MySQL syntax error).
+    /// Distinct from `supports_display_width`: that flag is about whether the
+    /// target *prints* MySQL-style `INT(11)` widths, not whether VARCHAR needs one.
+    pub requires_explicit_varchar_length: bool,
     /// Cap for length params when applying `{}` templates (e.g. Access TEXT max 255).
     pub max_varchar_len: Option<u32>,
     /// MySQL-style inline `COMMENT '...'` on columns.
@@ -314,6 +319,7 @@ fn mysql_family(db: DatabaseType) -> DdlDialectProfile {
         quote: QuoteStyle::Backtick,
         auto_inc: AutoIncSyntax::Suffix(" AUTO_INCREMENT"),
         supports_display_width: true,
+        requires_explicit_varchar_length: true,
         max_varchar_len: Some(65_535),
         inline_column_comment: true,
         foreign_keys_inline_in_create: false,
@@ -359,6 +365,7 @@ fn postgres_family(db: DatabaseType) -> DdlDialectProfile {
         quote: QuoteStyle::DoubleQuote,
         auto_inc: AutoIncSyntax::PostgresSequence,
         supports_display_width: false,
+        requires_explicit_varchar_length: false,
         max_varchar_len: None,
         inline_column_comment: false,
         foreign_keys_inline_in_create: false,
@@ -404,6 +411,10 @@ fn oracle_family(db: DatabaseType) -> DdlDialectProfile {
         quote: QuoteStyle::UnquotedUpper,
         auto_inc: AutoIncSyntax::Suffix(" GENERATED BY DEFAULT AS IDENTITY"),
         supports_display_width: false,
+        // Oracle's VARCHAR2 also rejects a missing length in real DDL, but this
+        // is left false (unverified, no Oracle instance in scope for this
+        // change) rather than asserting untested cross-dialect behavior.
+        requires_explicit_varchar_length: false,
         max_varchar_len: Some(4000),
         inline_column_comment: false,
         foreign_keys_inline_in_create: false,
@@ -450,6 +461,7 @@ fn sqlserver_family(db: DatabaseType) -> DdlDialectProfile {
         quote: QuoteStyle::Brackets,
         auto_inc: AutoIncSyntax::Suffix(" IDENTITY(1,1)"),
         supports_display_width: false,
+        requires_explicit_varchar_length: false,
         max_varchar_len: None,
         inline_column_comment: false,
         foreign_keys_inline_in_create: false,
@@ -495,6 +507,7 @@ fn sqlite_family(db: DatabaseType) -> DdlDialectProfile {
         quote: QuoteStyle::DoubleQuote,
         auto_inc: AutoIncSyntax::None,
         supports_display_width: false,
+        requires_explicit_varchar_length: false,
         max_varchar_len: None,
         inline_column_comment: false,
         foreign_keys_inline_in_create: true,
@@ -540,6 +553,7 @@ fn access_profile() -> DdlDialectProfile {
         quote: QuoteStyle::DoubleQuote,
         auto_inc: AutoIncSyntax::ReplaceTypeWith("COUNTER"),
         supports_display_width: false,
+        requires_explicit_varchar_length: false,
         max_varchar_len: Some(255),
         inline_column_comment: false,
         foreign_keys_inline_in_create: false,
@@ -585,6 +599,7 @@ fn h2_profile() -> DdlDialectProfile {
         quote: QuoteStyle::DoubleQuote,
         auto_inc: AutoIncSyntax::None,
         supports_display_width: false,
+        requires_explicit_varchar_length: false,
         max_varchar_len: None,
         inline_column_comment: false,
         foreign_keys_inline_in_create: false,
@@ -630,6 +645,12 @@ fn conservative_ansi(db: DatabaseType) -> DdlDialectProfile {
         quote: QuoteStyle::DoubleQuote,
         auto_inc: AutoIncSyntax::None,
         supports_display_width: false,
+        // This fallback also covers DB2 and Informix, which reject a bare
+        // VARCHAR with no length — but it's shared with dialects that don't
+        // (Snowflake, BigQuery, DuckDB, Trino, ...), so it can't be flipped
+        // true here without a dedicated DB2/Informix profile and DB
+        // verification. Tracked as a known gap, not fixed by this flag.
+        requires_explicit_varchar_length: false,
         max_varchar_len: None,
         inline_column_comment: false,
         foreign_keys_inline_in_create: false,

crates/dbx-core/src/sql_dialect/type_rewrite.rs

@@ -343,10 +343,33 @@ pub fn rewrite_column_type(source_type: &str, target: DatabaseType, source_diale
     // Dialect-kind matrix
     if let Some(src) = source_dialect {
         let target_kind = DialectKind::from_database_type(target);
-        let matrix = TypeMappingMatrix::for_dialects(src, target_kind);
-        let (converted, _) = matrix.convert_type(source_type);
-        if converted != source_type {
-            return strip_display_width_if_needed(&converted, &profile);
+        if src != target_kind {
+            let matrix = TypeMappingMatrix::for_dialects(src, target_kind);
+            let (converted, _) = matrix.convert_type(source_type);
+            if converted != source_type {
+                return strip_display_width_if_needed(&converted, &profile);
+            }
+            // No matrix rule for this cross-dialect pair, and it's a
+            // *varying*-length string type reported without a length — e.g.
+            // Postgres/Kingbase's unbounded `character varying` via
+            // format_type(). A bare passthrough would be invalid DDL for a
+            // target that requires an explicit VARCHAR length (MySQL and its
+            // family: VARCHAR/CHARACTER VARYING with no length is a syntax
+            // error there). Default to 255, matching the same fallback
+            // apply_template() already uses when a mapped type's length is
+            // missing. CHAR/CHARACTER are deliberately excluded: MySQL
+            // accepts a bare CHAR as CHAR(1), so defaulting it to 255 would
+            // silently change valid output into a different, wrong length.
+            // VARCHAR2/NVARCHAR2 are also excluded: they aren't valid MySQL
+            // type names at all, with or without a length, so defaulting
+            // their length fixes nothing.
+            if params.is_none()
+                && profile.requires_explicit_varchar_length
+                && profile.max_varchar_len.is_some()
+                && matches!(base.as_str(), "VARCHAR" | "CHARACTER VARYING" | "NVARCHAR")
+            {
+                return format!("{}(255)", source_type.trim());
+            }
         }
     }
 
@@ -509,6 +532,45 @@ mod tests {
         assert_eq!(t, "int(11)");
     }
 
+    #[test]
+    fn mysql_defaults_missing_length_on_cross_dialect_varchar() {
+        // Postgres/Kingbase report an unbounded varchar column as a bare
+        // `character varying` (no length) via format_type(). MySQL's
+        // VARCHAR/CHARACTER VARYING requires an explicit length, so passing
+        // that through verbatim is a syntax error (issue #8011).
+        let source = Some(DialectKind::Postgres);
+        assert_eq!(rewrite_column_type("character varying", DatabaseType::Mysql, source), "character varying(255)");
+        assert_eq!(rewrite_column_type("varchar", DatabaseType::Mysql, source), "varchar(255)");
+    }
+
+    #[test]
+    fn mysql_leaves_bare_char_untouched() {
+        // Unlike VARCHAR, a bare CHAR/CHARACTER is already valid MySQL
+        // syntax (implicitly CHAR(1)); defaulting it to 255 would silently
+        // change correct output into a different, wrong length.
+        let source = Some(DialectKind::Postgres);
+        assert_eq!(rewrite_column_type("character", DatabaseType::Mysql, source), "character");
+        assert_eq!(rewrite_column_type("char", DatabaseType::Mysql, source), "char");
+    }
+
+    #[test]
+    fn mysql_keeps_explicit_length_on_cross_dialect_varchar() {
+        let source = Some(DialectKind::Postgres);
+        assert_eq!(
+            rewrite_column_type("character varying(120)", DatabaseType::Mysql, source),
+            "character varying(120)"
+        );
+    }
+
+    #[test]
+    fn mysql_same_dialect_varchar_is_untouched_regardless_of_length() {
+        // Same-dialect metadata (or unknown source dialect) must never be
+        // rewritten — only a genuine cross-dialect gap should trigger the
+        // missing-length default.
+        assert_eq!(rewrite_column_type("varchar(255)", DatabaseType::Mysql, Some(DialectKind::Mysql)), "varchar(255)");
+        assert_eq!(rewrite_column_type("varchar(255)", DatabaseType::Mysql, None), "varchar(255)");
+    }
+
     #[test]
     fn normalize_len_params_strips_oracle_char_unit() {
         assert_eq!(normalize_len_params("(6 CHAR)"), "(6)");