[DRAFT] add raw explain

internal/cmd/cmd.go

@@ -48,6 +48,7 @@ func Do(args []string, stdin io.Reader, stdout io.Writer, stderr io.Writer) int
 	rootCmd.AddCommand(verifyCmd)
 	rootCmd.AddCommand(pushCmd)
 	rootCmd.AddCommand(NewCmdVet())
+	rootCmd.AddCommand(NewCmdExplain())
 
 	rootCmd.SetArgs(args)
 	rootCmd.SetIn(stdin)

internal/cmd/explain.go

@@ -0,0 +1,280 @@
+package cmd
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"runtime/trace"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/spf13/cobra"
+	"github.com/sqlc-dev/sqlc/internal/config"
+	"github.com/sqlc-dev/sqlc/internal/dbmanager"
+	"github.com/sqlc-dev/sqlc/internal/debug"
+	"github.com/sqlc-dev/sqlc/internal/opts"
+	"github.com/sqlc-dev/sqlc/internal/plugin"
+	"github.com/sqlc-dev/sqlc/internal/shfmt"
+	"gopkg.in/yaml.v3"
+)
+
+func NewCmdExplain() *cobra.Command {
+	return &cobra.Command{
+		Use:   "explain",
+		Short: "Explain queries",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			defer trace.StartRegion(cmd.Context(), "vet").End()
+			stderr := cmd.ErrOrStderr()
+			opts := &Options{
+				Env:    ParseEnv(cmd),
+				Stderr: stderr,
+			}
+			dir, name := getConfigPath(stderr, cmd.Flag("file"))
+			if err := Explain(cmd.Context(), dir, name, opts); err != nil {
+				if !errors.Is(err, ErrFailedChecks) {
+					fmt.Fprintf(stderr, "%s\n", err)
+				}
+				os.Exit(1)
+			}
+			return nil
+		},
+	}
+}
+
+func Explain(ctx context.Context, dir, filename string, opts *Options) error {
+	e := opts.Env
+	stderr := opts.Stderr
+	configPath, conf, err := readConfig(stderr, dir, filename)
+	if err != nil {
+		return err
+	}
+
+	base := filepath.Base(configPath)
+	if err := config.Validate(conf); err != nil {
+		fmt.Fprintf(stderr, "error validating %s: %s\n", base, err)
+		return err
+	}
+
+	if err := e.Validate(conf); err != nil {
+		fmt.Fprintf(stderr, "error validating %s: %s\n", base, err)
+		return err
+	}
+
+	c := rawExplainer{
+		Conf:          conf,
+		Dir:           dir,
+		Stderr:        stderr,
+		OnlyManagedDB: e.Debug.OnlyManagedDatabases,
+		Replacer:      shfmt.NewReplacer(nil),
+	}
+	var errs error
+	for _, sql := range conf.SQL {
+		if err := c.explainSQL(ctx, sql); err != nil {
+			fmt.Fprintf(stderr, "%s\n", err)
+			errs = errors.Join(errs, err)
+		}
+	}
+
+	return errs
+}
+
+type rawExplainer struct {
+	Conf          *config.Config
+	Dir           string
+	Stderr        io.Writer
+	OnlyManagedDB bool
+	Client        dbmanager.Client
+	Replacer      *shfmt.Replacer
+}
+
+func (c *rawExplainer) fetchDatabaseUri(ctx context.Context, s config.SQL) (string, func() error, error) {
+	return (&checker{
+		Conf:          c.Conf,
+		Dir:           c.Dir,
+		Stderr:        c.Stderr,
+		OnlyManagedDB: c.OnlyManagedDB,
+		Client:        c.Client,
+		Replacer:      c.Replacer,
+	}).fetchDatabaseUri(ctx, s)
+}
+
+func (c *rawExplainer) explainSQL(ctx context.Context, s config.SQL) error {
+	// TODO: Create a separate function for this logic so we can
+	combo := config.Combine(*c.Conf, s)
+
+	// TODO: This feels like a hack that will bite us later
+	joined := make([]string, 0, len(s.Schema))
+	for _, s := range s.Schema {
+		joined = append(joined, filepath.Join(c.Dir, s))
+	}
+	s.Schema = joined
+
+	joined = make([]string, 0, len(s.Queries))
+	for _, q := range s.Queries {
+		joined = append(joined, filepath.Join(c.Dir, q))
+	}
+	s.Queries = joined
+
+	var name string
+	parseOpts := opts.Parser{
+		Debug: debug.Debug,
+	}
+
+	result, failed := parse(ctx, name, c.Dir, s, combo, parseOpts, c.Stderr)
+	if failed {
+		return ErrFailedChecks
+	}
+
+	var expl rawDBExplainer
+	if s.Database != nil { // TODO only set up a database connection if a rule evaluation requires it
+		if s.Database.URI != "" && c.OnlyManagedDB {
+			return fmt.Errorf("database: connections disabled via SQLCDEBUG=databases=managed")
+		}
+		dburl, cleanup, err := c.fetchDatabaseUri(ctx, s)
+		if err != nil {
+			return err
+		}
+		defer func() {
+			if err := cleanup(); err != nil {
+				fmt.Fprintf(c.Stderr, "error cleaning up: %s\n", err)
+			}
+		}()
+
+		switch s.Engine {
+		case config.EnginePostgreSQL:
+			conn, err := pgx.Connect(ctx, dburl)
+			if err != nil {
+				return fmt.Errorf("database: connection error: %s", err)
+			}
+			if err := conn.Ping(ctx); err != nil {
+				return fmt.Errorf("database: connection error: %s", err)
+			}
+			defer conn.Close(ctx)
+
+			expl = &rawPostgresExplainer{c: conn}
+		case config.EngineMySQL:
+			db, err := sql.Open("mysql", dburl)
+			if err != nil {
+				return fmt.Errorf("database: connection error: %s", err)
+			}
+			if err := db.PingContext(ctx); err != nil {
+				return fmt.Errorf("database: connection error: %s", err)
+			}
+			defer db.Close()
+			expl = &rawMySQLExplainer{db}
+		case config.EngineSQLite:
+			db, err := sql.Open("sqlite", dburl)
+			if err != nil {
+				return fmt.Errorf("database: connection error: %s", err)
+			}
+			if err := db.PingContext(ctx); err != nil {
+				return fmt.Errorf("database: connection error: %s", err)
+			}
+			defer db.Close()
+			// SQLite really doesn't want us to depend on the output of EXPLAIN
+			// QUERY PLAN: https://www.sqlite.org/eqp.html
+			expl = nil
+		default:
+			return fmt.Errorf("unsupported database uri: %s", s.Engine)
+		}
+
+		req := codeGenRequest(result, combo)
+		for _, query := range req.Queries {
+			if expl == nil {
+				fmt.Fprintf(c.Stderr, "%s: %s: %s: error explaining query: database connection required\n", query.Filename, query.Name, name)
+				continue
+			}
+			results, err := expl.Explain(ctx, query.Text, query.Params...)
+			if err != nil {
+				fmt.Fprintf(c.Stderr, "%s: %s: %s: error explaining query: %s\n", query.Filename, query.Name, name, err)
+			}
+
+			err = yaml.NewEncoder(os.Stdout).Encode([]struct {
+				Name      string
+				Query     string `yaml:",flow"` // https://github.com/go-yaml/yaml/issues/789
+				Arguments []any
+				Output    interface{}
+			}{{
+				Name:      query.Name,
+				Query:     query.Text,
+				Arguments: expl.DefaultValues(query.Params),
+				Output:    string(results),
+			}})
+			if err != nil {
+				fmt.Fprintf(c.Stderr, "%s: %s: %s: fail marshal results: %s\n", query.Filename, query.Name, name, err)
+			}
+
+		}
+	}
+	return nil
+}
+
+type rawDBExplainer interface {
+	DefaultValues([]*plugin.Parameter) []any
+	Explain(context.Context, string, ...*plugin.Parameter) ([]byte, error)
+}
+
+type rawPostgresExplainer struct {
+	c *pgx.Conn
+}
+
+func (p *rawPostgresExplainer) DefaultValues(args []*plugin.Parameter) []any {
+	eArgs := make([]any, len(args))
+	for i, a := range args {
+		eArgs[i] = pgDefaultValue(a.Column)
+	}
+	return eArgs
+}
+
+func (p *rawPostgresExplainer) Explain(ctx context.Context, query string, args ...*plugin.Parameter) ([]byte, error) {
+	eQuery := "EXPLAIN " + query
+	eArgs := p.DefaultValues(args)
+	var results []byte
+
+	rows, err := p.c.Query(ctx, eQuery, eArgs...)
+	if err != nil {
+		return nil, err
+	}
+	for rows.Next() {
+		var result []byte
+		err := rows.Scan(&result)
+		if err != nil {
+			return nil, err
+		}
+		results = append(results, append(result, '\n')...)
+	}
+	return results, nil
+}
+
+type rawMySQLExplainer struct {
+	*sql.DB
+}
+
+func (me *rawMySQLExplainer) DefaultValues(args []*plugin.Parameter) []any {
+	eArgs := make([]any, len(args))
+	for i, a := range args {
+		eArgs[i] = mysqlDefaultValue(a.Column)
+	}
+	return eArgs
+}
+func (me *rawMySQLExplainer) Explain(ctx context.Context, query string, args ...*plugin.Parameter) ([]byte, error) {
+	eQuery := "EXPLAIN " + query
+	eArgs := me.DefaultValues(args)
+	var results []byte
+	rows, err := me.QueryContext(ctx, eQuery, eArgs...)
+	if err != nil {
+		return nil, err
+	}
+	for rows.Next() {
+		var result []byte
+		err := rows.Scan(&result)
+		if err != nil {
+			return nil, err
+		}
+		results = append(results, append(result, '\n')...)
+	}
+	return results, nil
+}