rustyroad 1.2.0

Rusty Road is a framework written in Rust that is based on Ruby on Rails. It is designed to provide the familiar conventions and ease of use of Ruby on Rails, while also taking advantage of the performance and efficiency of Rust.
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//! Planning `alter_column`, the breaking-change case.

use super::super::duplicate::Duplicate;
use super::super::model::AlterColumn;
use super::super::trigger::{Direction, Trigger};
use super::super::{new_ref, Plan};

/// Alters a column via a shadow copy kept in sync in both directions.
///
/// The original column is left untouched during `start`, so readers of the old
/// schema version continue to work. Both are promoted at completion.
pub(super) fn plan(op: &AlterColumn, latest_schema: &str) -> Plan {
    let duplicate = Duplicate {
        table: &op.table,
        column: &op.column,
        column_type: op.column_type.as_deref(),
        nullable: op.nullable.unwrap_or(true),
        default: None,
    };

    let mut plan = Plan {
        statements: vec![duplicate.add_column()],
        ..Plan::default()
    };

    // Forward: old column to shadow, for readers of the new version.
    let shadow = duplicate.shadow_name();
    let default_up = new_ref(&op.column);
    plan.statements.extend(
        Trigger {
            table: &op.table,
            physical_column: &shadow,
            direction: Direction::Up,
            expression: op.up.as_deref().unwrap_or(&default_up),
            latest_schema,
        }
        .install(),
    );

    // Reverse: shadow back to old column, so readers of the old version keep working.
    if let Some(down) = &op.down {
        plan.statements.extend(
            Trigger {
                table: &op.table,
                physical_column: &op.column,
                direction: Direction::Down,
                expression: down,
                latest_schema,
            }
            .install(),
        );
    }

    plan.backfill_tables.push(op.table.clone());
    plan.promotions.push((op.table.clone(), op.column.clone()));
    if let Some(name) = &op.name {
        plan.renames
            .push((op.table.clone(), op.column.clone(), name.clone()));
    }

    plan
}