Automatically infer migration type

sqlx-cli/README.md

@@ -72,7 +72,7 @@ sqlx migrate info --source ../relative/migrations
 
 ### Reverting Migrations
 
-If you would like to create _reversible_ migrations with corresponding "up" and "down" scripts, you use the `-r` flag when creating new migrations:
+If you would like to create _reversible_ migrations with corresponding "up" and "down" scripts, you use the `-r` flag when creating the first migration:
 
 ```bash
 $ sqlx migrate add -r <name>
@@ -94,14 +94,12 @@ $ sqlx migrate revert
 Applied 20211001154420/revert <name>
 ```
 
-**Note**: attempting to mix "simple" migrations with reversible migrations with result in an error.
+**Note**: All the subsequent migrations will be reversible as well.
 
 ```bash
 $ sqlx migrate add <name1>
-Creating migrations/20211001154420_<name>.sql
-
-$ sqlx migrate add -r <name2>
-error: cannot mix reversible migrations with simple migrations. All migrations should be reversible or simple migrations
+Creating migrations/20211001154420_<name>.up.sql
+Creating migrations/20211001154420_<name>.down.sql
 ```
 
 ### Enable building in "offline mode" with `query!()`

sqlx-cli/src/migrate.rs

@@ -115,17 +115,14 @@ pub async fn add(
         .unwrap_or(false);
 
     let migrator = Migrator::new(Path::new(migration_source)).await?;
-    // This checks if all existing migrations are of the same type as the reversible flag passed
-    for migration in migrator.iter() {
-        if migration.migration_type.is_reversible() != reversible {
-            bail!(MigrateError::InvalidMixReversibleAndSimple);
-        }
-    }
+    // Type of newly created migration will be the same as the first one
+    // or reversible flag if this is the first migration
+    let migration_type = MigrationType::infer(&migrator, reversible);
 
     let ordering = MigrationOrdering::infer(sequential, timestamp, &migrator);
     let file_prefix = ordering.file_prefix();
 
-    if reversible {
+    if migration_type.is_reversible() {
         create_file(
             migration_source,
             &file_prefix,

sqlx-core/src/migrate/error.rs

@@ -24,6 +24,7 @@ pub enum MigrateError {
     #[error("migration {0} is newer than the latest applied migration {1}")]
     VersionTooNew(i64, i64),
 
+    #[deprecated = "migration types are now inferred"]
     #[error("cannot mix reversible migrations with simple migrations. All migrations should be reversible or simple migrations")]
     InvalidMixReversibleAndSimple,
 

sqlx-core/src/migrate/migration_type.rs

@@ -1,3 +1,5 @@
+use super::Migrator;
+
 /// Migration Type represents the type of migration
 #[derive(Debug, Copy, Clone, PartialEq)]
 pub enum MigrationType {
@@ -71,4 +73,17 @@ impl MigrationType {
             MigrationType::ReversibleDown => "-- Add down migration script here\n",
         }
     }
+
+    pub fn infer(migrator: &Migrator, reversible: bool) -> MigrationType {
+        match migrator.iter().next() {
+            Some(first_migration) => first_migration.migration_type,
+            None => {
+                if reversible {
+                    MigrationType::ReversibleUp
+                } else {
+                    MigrationType::Simple
+                }
+            }
+        }
+    }
 }