Add set_config and the transaction mode checks after a query

CHANGELOG.md

@@ -4,6 +4,14 @@ All changes that a user can see are in this file. The version is 0.M.patch, wher
 
 ## Unreleased
 
+### Added
+
+- `set_config` (spec/06 section 6.13), which is `SET` as a function. It takes the same values and gives the same errors as `SET`, and gives the new value as `SHOW` does. A null value resets the parameter. The change counts for the rest of the query, so a `set_config` of `TimeZone` changes the output of the values after it in the same row. An error or a rollback undoes the change, and a local change ends with its transaction.
+
+### Fixed
+
+- After the first query of a transaction, `SET TRANSACTION ISOLATION LEVEL` with a new level, `SET TRANSACTION [NOT] DEFERRABLE` and `SET TRANSACTION READ WRITE` in a read-only transaction now give `25001`, as in PostgreSQL. A query takes the snapshot of the transaction when it is analyzed, in a `Query` or a `Parse` message.
+
 ## 0.0.18 (2026-10-08)
 
 The eighteenth patch release on the 0.0 line. `SELECT` now has subqueries in expressions, the 12 OID alias types such as `regclass` and `regtype`, and the catalog visibility and comment functions. No crate is published.

crates/rupg-exec/src/tests.rs

@@ -1,3 +1,5 @@
+use std::rc::Rc;
+
 use rupg_analyze::{Env, Params, analyze};
 use rupg_common::Result;
 use rupg_sql::nodes::Node;
@@ -9,7 +11,7 @@ use crate::prepare;
 
 /// A session at 2000-01-11 00:00 UTC with the default settings.
 struct TestSession {
-    zone: FixedZone,
+    zone: Rc<FixedZone>,
 }
 
 impl rupg_func::Session for TestSession {
@@ -19,8 +21,8 @@ impl rupg_func::Session for TestSession {
     fn interval_style(&self) -> IntervalStyle {
         IntervalStyle::Postgres
     }
-    fn zone(&self) -> Result<&dyn TimeZone> {
-        Ok(&self.zone)
+    fn zone(&self) -> Result<Rc<dyn TimeZone>> {
+        Ok(Rc::clone(&self.zone) as Rc<dyn TimeZone>)
     }
     fn extra_float_digits(&self) -> i32 {
         1
@@ -61,6 +63,9 @@ impl rupg_func::Session for TestSession {
     fn setting(&self, _: &str) -> Option<String> {
         None
     }
+    fn set_setting(&self, _: &str, _: Option<&str>, _: bool) -> Result<String> {
+        Err(rupg_common::Error::internal("the test session has no settings to change"))
+    }
 }
 
 impl Env for TestSession {
@@ -87,7 +92,7 @@ impl Env for TestSession {
 
 /// The text of each column of each row of a query, `NULL` for a null value, or the error.
 fn run(sql: &str) -> Result<Vec<Vec<String>>> {
-    let session = TestSession { zone: FixedZone::utc() };
+    let session = TestSession { zone: Rc::new(FixedZone::utc()) };
     let (stmts, _) = rupg_sql::parse(sql).map_err(rupg_common::Error::from)?;
     let Some(Some(Node::RawStmt(raw))) = stmts.first() else { panic!("no statement in {sql}") };
     let query = analyze(raw.stmt.as_ref().expect("a statement"), &session, &Params::default())?;

crates/rupg-func/src/io.rs

@@ -155,7 +155,7 @@ pub fn output(ty: u32, value: &Value, session: &dyn Session, out: &mut Vec<u8>)
             types::timestamp_out(*v, session.date_format(), out).map_err(type_error)?;
         }
         (_, Value::TimestampTz(v)) => {
-            types::timestamptz_out(*v, session.date_format(), session.zone()?, out)
+            types::timestamptz_out(*v, session.date_format(), &*session.zone()?, out)
                 .map_err(type_error)?;
         }
         (_, Value::Interval(v)) => types::interval_out(v, session.interval_style(), out),
@@ -249,7 +249,7 @@ pub fn input(ty: u32, text: &str, typmod: i32, session: &dyn Session) -> Result<
         }
         oid::DATE | oid::TIME | oid::TIMETZ | oid::TIMESTAMP | oid::TIMESTAMPTZ => {
             let zone = session.zone()?;
-            let cx = datetime_input(session, zone);
+            let cx = datetime_input(session, &*zone);
             match ty {
                 oid::DATE => Value::Date(types::date_in(text, &cx).map_err(type_error)?),
                 oid::TIME => Value::Time(types::time_in(text, typmod, &cx).map_err(type_error)?),

crates/rupg-func/src/lib.rs

@@ -15,6 +15,7 @@ mod reg;
 mod text;
 
 use std::collections::BTreeMap;
+use std::rc::Rc;
 use std::sync::OnceLock;
 
 use rupg_common::{Error, Result, SqlState};
@@ -39,7 +40,7 @@ pub trait Session {
     /// # Errors
     ///
     /// `0A000` for a zone whose rules the engine does not have yet.
-    fn zone(&self) -> Result<&dyn TimeZone>;
+    fn zone(&self) -> Result<Rc<dyn TimeZone>>;
     /// The `extra_float_digits` setting.
     fn extra_float_digits(&self) -> i32;
     /// The `bytea_output` setting.
@@ -66,6 +67,12 @@ pub trait Session {
     fn version(&self) -> String;
     /// The value of a setting as `SHOW` gives it, or `None` for a name that is not a setting.
     fn setting(&self, name: &str) -> Option<String>;
+    /// `set_config_option` for `set_config`: sets a parameter for the session, or for the transaction when `local` is true, and gives the new value as `SHOW` gives it. `value` is `None` for a reset.
+    ///
+    /// # Errors
+    ///
+    /// The errors of `SET` for the name and the value.
+    fn set_setting(&self, name: &str, value: Option<&str>, local: bool) -> Result<String>;
 }
 
 /// A call of a function.

crates/rupg-func/src/misc.rs

@@ -145,6 +145,27 @@ fn current_setting(call: &Call<'_>, args: &[Value]) -> Result<Value> {
     ))
 }
 
+/// `set_config_by_name`: `set_config`, which is `SET` as a function. A null value resets the parameter, and a null `is_local` is false.
+fn set_config(call: &Call<'_>, args: &[Value]) -> Result<Value> {
+    let name = match args.first() {
+        Some(Value::Null) => {
+            return Err(Error::new(
+                SqlState::NULL_VALUE_NOT_ALLOWED,
+                "SET requires parameter name",
+            ));
+        }
+        Some(name) => name.as_str().ok_or_else(bad_value)?,
+        None => return Err(bad_value()),
+    };
+    let value = match args.get(1) {
+        Some(Value::Null) => None,
+        Some(value) => Some(value.as_str().ok_or_else(bad_value)?),
+        None => return Err(bad_value()),
+    };
+    let local = args.get(2).and_then(Value::as_bool).unwrap_or(false);
+    Ok(Value::Text(call.session.set_setting(name, value, local)?))
+}
+
 /// The kernel of a function of this module by its `prosrc`.
 pub(crate) fn by_src(src: &str) -> Option<Kernel> {
     Some(match src {
@@ -162,6 +183,7 @@ pub(crate) fn by_src(src: &str) -> Option<Kernel> {
         "pg_client_encoding" => pg_client_encoding,
         "format_type" => format_type,
         "show_config_by_name" | "show_config_by_name_missing_ok" => current_setting,
+        "set_config_by_name" => set_config,
         _ => return None,
     })
 }

crates/rupg-func/src/tests.rs

@@ -1,3 +1,5 @@
+use std::rc::Rc;
+
 use rupg_common::{Result, SqlState};
 use rupg_pgcatalog::builtin;
 use rupg_types::{
@@ -8,12 +10,12 @@ use rupg_types::{
 use crate::{Call, Session, kernel, output};
 
 struct TestSession {
-    zone: FixedZone,
+    zone: Rc<FixedZone>,
 }
 
 impl TestSession {
     fn new() -> TestSession {
-        TestSession { zone: FixedZone::utc() }
+        TestSession { zone: Rc::new(FixedZone::utc()) }
     }
 }
 
@@ -24,8 +26,8 @@ impl Session for TestSession {
     fn interval_style(&self) -> IntervalStyle {
         IntervalStyle::Postgres
     }
-    fn zone(&self) -> Result<&dyn TimeZone> {
-        Ok(&self.zone)
+    fn zone(&self) -> Result<Rc<dyn TimeZone>> {
+        Ok(Rc::clone(&self.zone) as Rc<dyn TimeZone>)
     }
     fn extra_float_digits(&self) -> i32 {
         1
@@ -66,6 +68,9 @@ impl Session for TestSession {
     fn setting(&self, name: &str) -> Option<String> {
         (name == "datestyle").then(|| "ISO, MDY".to_string())
     }
+    fn set_setting(&self, _: &str, _: Option<&str>, _: bool) -> Result<String> {
+        Err(rupg_common::Error::internal("the test session has no settings to change"))
+    }
 }
 
 /// A call of the function in `pg_catalog` with this name and these argument types.