Add an experimental transpile command

This is still pretty basic.

src/cmd/mod.rs

@@ -2,3 +2,4 @@
 
 pub mod parse;
 pub mod sql_test;
+pub mod transpile;

src/cmd/transpile.rs

@@ -0,0 +1,50 @@
+//! Transpile code to another dialect of SQL.
+
+use std::path::PathBuf;
+
+use clap::Parser;
+use tracing::instrument;
+
+use crate::{
+    ast::{parse_sql, Emit},
+    drivers,
+    errors::{Context, Result},
+};
+
+/// Run SQL tests from a directory.
+#[derive(Debug, Parser)]
+pub struct TranspileOpt {
+    /// An SQL file to transpile.
+    sql_path: PathBuf,
+
+    /// A database locator to run tests against. (For now, this must be a
+    /// an actual database locator, and not the name of a dialect.)
+    #[clap(long, visible_alias = "db", default_value = "sqlite3::memory:")]
+    database: String,
+}
+
+/// Run our SQL test suite.
+#[instrument(skip(opt))]
+pub async fn cmd_transpile(opt: &TranspileOpt) -> Result<()> {
+    // Get a database driver for our target.
+    let locator = opt.database.parse::<Box<dyn drivers::Locator>>()?;
+    let driver = locator.driver().await?;
+
+    // Parse our SQL.
+    let sql = tokio::fs::read_to_string(&opt.sql_path)
+        .await
+        .with_context(|| format!("could not read SQL file {}", opt.sql_path.display()))?;
+    let ast = parse_sql(&opt.sql_path, &sql)?;
+    let rewritten_ast = driver.rewrite_ast(&ast)?;
+
+    // Print our rewritten AST.
+    for statement in rewritten_ast.extra.native_setup_sql {
+        println!("{};", statement);
+    }
+    let transpiled_sql = rewritten_ast.ast.emit_to_string(locator.target());
+    println!("{}", transpiled_sql);
+    for statement in rewritten_ast.extra.native_teardown_sql {
+        println!("{};", statement);
+    }
+    Ok(())
+}

src/main.rs

@@ -14,6 +14,7 @@ mod util;
 use cmd::{
     parse::{cmd_parse, ParseOpt},
     sql_test::{cmd_sql_test, SqlTestOpt},
+    transpile::{cmd_transpile, TranspileOpt},
 };
 use tracing::info_span;
 
@@ -23,6 +24,8 @@ enum Opt {
     Parse(ParseOpt),
     /// Run SQL tests from a directory.
     SqlTest(SqlTestOpt),
+    /// Transpile BigQuery SQL to another dialect.
+    Transpile(TranspileOpt),
 }
 
 #[tokio::main]
@@ -35,6 +38,7 @@ async fn main() {
     let result = match opt {
         Opt::Parse(parse_opt) => cmd_parse(&parse_opt),
         Opt::SqlTest(sql_test_opt) => cmd_sql_test(&sql_test_opt).await,
+        Opt::Transpile(transpile_opt) => cmd_transpile(&transpile_opt).await,
     };
     if let Err(e) = result {
         e.emit();