Improve error messages (#354)

Include detail and hint fields for conn execution errors. This is
crucial for certain types of errors (e.g., unable to connect to
PostgreSQL source), where the true cause of the error message is only
returned in the detail field.

pkg/materialize/generic.go

@@ -1,9 +1,11 @@
 package materialize
 
 import (
+	"errors"
 	"fmt"
 	"log"
 
+	"github.com/jackc/pgx"
 	"github.com/jmoiron/sqlx"
 )
 
@@ -41,6 +43,19 @@ func (b *Builder) exec(statement string) error {
 	_, err := b.conn.Exec(statement)
 	if err != nil {
 		log.Printf("[DEBUG] error executing: %s", statement)
+		var pgErr pgx.PgError
+		pgErr, ok := err.(pgx.PgError)
+		if ok {
+			msg := fmt.Sprintf("%s: %s", pgErr.Severity, pgErr.Message)
+			if pgErr.Detail != "" {
+				msg += fmt.Sprintf(" DETAIL: %s", pgErr.Detail)
+			}
+			if pgErr.Hint != "" {
+				msg += fmt.Sprintf(" HINT: %s", pgErr.Hint)
+			}
+			msg += fmt.Sprintf(" (SQLSTATE %s)", pgErr.SQLState())
+			return errors.New(msg)
+		}
 		return err
 	}