Struct SessionVariableSyntax 

pub struct SessionVariableSyntax {
    pub user_variables: bool,
    pub system_variables: bool,
    pub variable_assignment: bool,
}

Dialect-owned MySQL session-variable syntax.

MySQL exposes user-defined @name variables and server @@[scope.]name system variables as value expressions — distinct from a prepared-statement placeholder (ParameterSyntax), which is a hole bound at execute time. Each flag is a lexical gate: it decides whether the scanner recognises that sigil as a variable token (Expr::SessionVariable) rather than a stray byte. The two forms are independent — a dialect can accept @@sysvar without @uservar — and are lookahead-disjoint (@@ needs a second @, @name an identifier-start), so they never contend with each other.

Fields

user_variables: bool

Accept @name user-defined session variables (MySQL). The sigil must abut an identifier-start byte. Mutually exclusive with ParameterSyntax::named_at: both claim @name, so enabling both is a LexicalConflict::AtNameParameterVersusUserVariable.

system_variables: bool

Accept @@name / @@global.name / @@session.name system variables (MySQL). The @@ must abut an identifier-start byte; a scoped form folds the optional global./session. prefix into the same token. Never contends with named_at or user_variables — the second @ keeps @@ lookahead-disjoint from the single-@ forms.

variable_assignment: bool

Accept the MySQL SET variable-assignment statement grammar and its := assignment operator (MySQL).

Two facets of one behaviour that ship together in MySQL and nowhere else:

• Parser — a SET becomes a comma-separated list of heterogeneous assignments (SessionStatement::SetVariables): [GLOBAL|SESSION|LOCAL|PERSIST|PERSIST_ONLY] <var> {= | :=} <expr>, the @@[scope.]<var> spellings, user variables @v {= | :=} <expr>, and SET {CHARACTER SET | CHARSET} …. Each value is a full expression, unlike the generic PostgreSQL SET’s restricted literal/bareword value list, so the two grammars are distinct statements rather than one widened form.
• Lexer — := lexes to the ColonEquals operator token (MySQL’s SET_VAR), the same token PostgreSQL’s deprecated named-argument separator produces; the two never coexist in a shipped preset, so the shared token is unambiguous per dialect.

The two facets sit on independent axes, which is why this flag is a documented exemption from the feature_dependencies registry rather than a FeatureDependencyViolation variant. The parser facet is unreachable without show_syntax.session_statements — the leader that dispatches every SET/RESET/SHOW, so with it off no SET form parses at all (measured: SET x = 1 is rejected as an unknown statement leader) — a genuine cross-axis grammar dependency. The lexer facet, however, fires whether or not that leader is on: with session_statements off, := still munches to one ColonEquals token (measured), so the flag is not inert without its parser-side base. A registry whose contract is inertness cannot own a flag that keeps changing tokenization while its base is off, so the dependency is recorded here instead. See the exemption note on feature_dependencies.

This is a route flag on the SET head — when on it dispatches the MySQL grammar before the standard SET TIME ZONE / SET SESSION AUTHORIZATION forms are read (see the parser’s parse_set) — but unlike the access_control_account_grants route it carries no GrammarConflict variant: the grammar it displaces is unconditional base grammar with no rival feature flag, so there is no independently-expressible both-on state, and MySQL (a shipped preset) already exercises the route deterministically. Registering it would require promoting the standard SET config grammar to its own flag or converting this field to an enum axis — see the GrammarConflict enum doc’s route-flag discussion.

Shared := claim with CallSyntax::named_argument (PostgreSQL named args): both enable := lexing; shipped presets never arm both, so the token stays unambiguous.

Implementations

impl SessionVariableSyntax

pub const ANSI: Self

The ANSI predefined value.

impl SessionVariableSyntax

pub const LENIENT: Self

Available on crate feature lenient only.

LENIENT: the @@[scope.]name MySQL system-variable form, additive over the @name parameter that ParameterSyntax::LENIENT already lexes (@@ is disjoint from @name by its second @). user_variables stays off: @name is claimed as a named-at parameter here, and the two meanings cannot both hold the trigger (a LexicalConflict).

impl SessionVariableSyntax

pub const MYSQL: Self

Available on crate feature mysql only.

The MYSQL preset for session variable syntax.

Trait Implementations

impl Clone for SessionVariableSyntax

fn clone(&self) -> SessionVariableSyntax

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for SessionVariableSyntax

impl Debug for SessionVariableSyntax

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for SessionVariableSyntax

impl PartialEq for SessionVariableSyntax

fn eq(&self, other: &SessionVariableSyntax) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for SessionVariableSyntax