fix: emit USING clause for ALTER COLUMN TYPE when base types differ (#537)

internal/diff/column.go

@@ -112,36 +112,34 @@ func (cd *ColumnDiff) generateColumnSQL(tableSchema, tableName string, targetSch
 
 // needsUsingClause determines if a type conversion requires a USING clause.
 //
-// This is especially important when converting to or from custom types (like ENUMs),
-// because PostgreSQL often cannot implicitly cast these types. To avoid generating
-// invalid migrations, this function takes a conservative approach:
-//
-//   - Any conversion involving at least one non–built-in (custom) type will require
-//     a USING clause.
-//   - For built-in → built-in conversions we still assume PostgreSQL provides an
-//     implicit cast in most cases; callers should be aware that some edge cases
-//     (e.g. certain text → json conversions) may still need manual adjustment.
+// PostgreSQL rejects bare ALTER COLUMN TYPE when no implicit cast exists between
+// the old and new types (SQLSTATE 42804). When the base type names differ, we
+// always emit USING col::newtype — a redundant USING is harmless when an implicit
+// cast exists, but a missing one breaks the migration. When only modifiers change
+// (e.g. numeric(18,6) → numeric(20,6)), no USING is needed.
 func needsUsingClause(oldType, newType string) bool {
-	// Check if old type is text-like
-	oldIsTextLike := ir.IsTextLikeType(oldType)
-
-	// Determine whether the old/new types are PostgreSQL built-ins
-	oldIsBuiltIn := ir.IsBuiltInType(oldType)
-	newIsBuiltIn := ir.IsBuiltInType(newType)
-
-	// Preserve existing behavior: text-like → non–built-in likely needs USING
-	if oldIsTextLike && !newIsBuiltIn {
-		return true
+	oldNorm := normalizeBaseTypeName(oldType)
+	newNorm := normalizeBaseTypeName(newType)
+	if oldNorm == newNorm {
+		return false
 	}
+	return true
+}
 
-	// Be conservative for any conversion involving custom (non–built-in) types:
-	// this covers custom → custom and built-in ↔ custom conversions.
-	if !oldIsBuiltIn || !newIsBuiltIn {
-		return true
+func normalizeBaseTypeName(typeName string) string {
+	t := typeName
+	if open := strings.Index(t, "("); open != -1 {
+		if close := strings.Index(t[open:], ")"); close != -1 {
+			t = t[:open] + t[open+close+1:]
+		} else {
+			t = t[:open]
+		}
 	}
-
-	// For built-in → built-in types we assume an implicit cast is available.
-	return false
+	t = strings.TrimPrefix(t, "pg_catalog.")
+	if !strings.Contains(t, "\"") {
+		t = strings.ToLower(t)
+	}
+	return t
 }
 
 // comparableColumnType returns the column's data type including any

internal/diff/column_test.go

@@ -0,0 +1,59 @@
+package diff
+
+import "testing"
+
+func TestNormalizeBaseTypeName(t *testing.T) {
+	tests := []struct {
+		input string
+		want  string
+	}{
+		{"integer", "integer"},
+		{"INTEGER", "integer"},
+		{"bigint", "bigint"},
+		{"numeric(18,6)", "numeric"},
+		{"numeric(20,6)", "numeric"},
+		{"varchar(128)", "varchar"},
+		{"character varying(255)", "character varying"},
+		{"integer[]", "integer[]"},
+		{"character varying(128)[]", "character varying[]"},
+		{"timestamp(6) with time zone", "timestamp with time zone"},
+		{"pg_catalog.int4", "int4"},
+		{`"MyStatus"`, `"MyStatus"`},
+		{`"mystatus"`, `"mystatus"`},
+		{`"MyStatus"[]`, `"MyStatus"[]`},
+	}
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			got := normalizeBaseTypeName(tt.input)
+			if got != tt.want {
+				t.Errorf("normalizeBaseTypeName(%q) = %q, want %q", tt.input, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestNeedsUsingClause(t *testing.T) {
+	tests := []struct {
+		old  string
+		new  string
+		want bool
+	}{
+		{"text", "integer", true},
+		{"integer", "bigint", true},
+		{"numeric(18,6)", "numeric(20,6)", false},
+		{"integer", "integer[]", true},
+		{"text", "action_type", true},
+		{"varchar(128)", "varchar(255)", false},
+		{"timestamp(3) with time zone", "timestamp(6) with time zone", false},
+		{"timestamp without time zone", "timestamp with time zone", true},
+		{`"MyStatus"`, `"mystatus"`, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.old+"→"+tt.new, func(t *testing.T) {
+			got := needsUsingClause(tt.old, tt.new)
+			if got != tt.want {
+				t.Errorf("needsUsingClause(%q, %q) = %v, want %v", tt.old, tt.new, got, tt.want)
+			}
+		})
+	}
+}

testdata/diff/create_table/alter_column_quoted_identifier/diff.sql

@@ -1 +1 @@
-ALTER TABLE ex ALTER COLUMN "ID" TYPE bigint;
+ALTER TABLE ex ALTER COLUMN "ID" TYPE bigint USING "ID"::bigint;

testdata/diff/create_table/alter_column_quoted_identifier/plan.json

@@ -1,6 +1,6 @@
 {
   "version": "1.0.0",
-  "pgschema_version": "1.12.1",
+  "pgschema_version": "1.12.2",
   "created_at": "1970-01-01T00:00:00Z",
   "source_fingerprint": {
     "hash": "9d443bc536153eed8fce077bfacc3d7f42b1a94f02d33868bb78be3b9de05088"
@@ -9,7 +9,7 @@
     {
       "steps": [
         {
-          "sql": "ALTER TABLE ex ALTER COLUMN \"ID\" TYPE bigint;",
+          "sql": "ALTER TABLE ex ALTER COLUMN \"ID\" TYPE bigint USING \"ID\"::bigint;",
           "type": "table.column",
           "operation": "alter",
           "path": "public.ex.ID"

testdata/diff/create_table/alter_column_quoted_identifier/plan.sql

@@ -1 +1 @@
-ALTER TABLE ex ALTER COLUMN "ID" TYPE bigint;
+ALTER TABLE ex ALTER COLUMN "ID" TYPE bigint USING "ID"::bigint;

testdata/diff/create_table/alter_column_quoted_identifier/plan.txt

@@ -10,4 +10,4 @@ Tables:
 DDL to be executed:
 --------------------------------------------------
 
-ALTER TABLE ex ALTER COLUMN "ID" TYPE bigint;
+ALTER TABLE ex ALTER COLUMN "ID" TYPE bigint USING "ID"::bigint;

testdata/diff/create_table/alter_column_types/diff.sql

@@ -4,11 +4,11 @@ CREATE TYPE action_type AS ENUM (
     'rejected'
 );
 
-ALTER TABLE user_pending_permissions ALTER COLUMN id TYPE bigint;
+ALTER TABLE user_pending_permissions ALTER COLUMN id TYPE bigint USING id::bigint;
 
-ALTER TABLE user_pending_permissions ALTER COLUMN user_id TYPE bigint;
+ALTER TABLE user_pending_permissions ALTER COLUMN user_id TYPE bigint USING user_id::bigint;
 
-ALTER TABLE user_pending_permissions ALTER COLUMN object_ids_ints TYPE bigint[];
+ALTER TABLE user_pending_permissions ALTER COLUMN object_ids_ints TYPE bigint[] USING object_ids_ints::bigint[];
 
 ALTER TABLE user_pending_permissions ALTER COLUMN action TYPE action_type USING action::action_type;
 
@@ -21,3 +21,11 @@ ALTER TABLE user_pending_permissions ALTER COLUMN status SET DEFAULT 'pending'::
 ALTER TABLE user_pending_permissions ALTER COLUMN tags TYPE action_type[] USING tags::action_type[];
 
 ALTER TABLE user_pending_permissions ALTER COLUMN amount TYPE numeric(20,6);
+
+ALTER TABLE user_pending_permissions ALTER COLUMN arfcn_dl DROP DEFAULT;
+
+ALTER TABLE user_pending_permissions ALTER COLUMN arfcn_dl TYPE integer USING arfcn_dl::integer;
+
+ALTER TABLE user_pending_permissions ALTER COLUMN arfcn_dl SET DEFAULT 0;
+
+ALTER TABLE user_pending_permissions ALTER COLUMN priority TYPE integer USING priority::integer;

testdata/diff/create_table/alter_column_types/new.sql

@@ -8,5 +8,7 @@ CREATE TABLE public.user_pending_permissions (
     action public.action_type,
     status public.action_type DEFAULT 'pending',
     tags public.action_type[],
-    amount numeric(20,6) NOT NULL DEFAULT 0
+    amount numeric(20,6) NOT NULL DEFAULT 0,
+    arfcn_dl integer DEFAULT 0,
+    priority integer
 );

testdata/diff/create_table/alter_column_types/old.sql

@@ -6,5 +6,7 @@ CREATE TABLE public.user_pending_permissions (
     action text,
     status text DEFAULT 'pending',
     tags text[],
-    amount numeric(18,6) NOT NULL DEFAULT 0
+    amount numeric(18,6) NOT NULL DEFAULT 0,
+    arfcn_dl text DEFAULT 'unknown',
+    priority text
 );

testdata/diff/create_table/alter_column_types/plan.json

@@ -1,9 +1,9 @@
 {
   "version": "1.0.0",
-  "pgschema_version": "1.12.1",
+  "pgschema_version": "1.12.2",
   "created_at": "1970-01-01T00:00:00Z",
   "source_fingerprint": {
-    "hash": "614655f95d349ec321da570d4e232db71f8bfb57404998153f9fd53720cd2acb"
+    "hash": "31ef5d21f4bfa9713df469db3eb54585bf60ea348f09608b21f7d05eae9f3f02"
   },
   "groups": [
     {
@@ -15,19 +15,19 @@
           "path": "public.action_type"
         },
         {
-          "sql": "ALTER TABLE user_pending_permissions ALTER COLUMN id TYPE bigint;",
+          "sql": "ALTER TABLE user_pending_permissions ALTER COLUMN id TYPE bigint USING id::bigint;",
           "type": "table.column",
           "operation": "alter",
           "path": "public.user_pending_permissions.id"
         },
         {
-          "sql": "ALTER TABLE user_pending_permissions ALTER COLUMN user_id TYPE bigint;",
+          "sql": "ALTER TABLE user_pending_permissions ALTER COLUMN user_id TYPE bigint USING user_id::bigint;",
           "type": "table.column",
           "operation": "alter",
           "path": "public.user_pending_permissions.user_id"
         },
         {
-          "sql": "ALTER TABLE user_pending_permissions ALTER COLUMN object_ids_ints TYPE bigint[];",
+          "sql": "ALTER TABLE user_pending_permissions ALTER COLUMN object_ids_ints TYPE bigint[] USING object_ids_ints::bigint[];",
           "type": "table.column",
           "operation": "alter",
           "path": "public.user_pending_permissions.object_ids_ints"
@@ -67,6 +67,30 @@
           "type": "table.column",
           "operation": "alter",
           "path": "public.user_pending_permissions.amount"
+        },
+        {
+          "sql": "ALTER TABLE user_pending_permissions ALTER COLUMN arfcn_dl DROP DEFAULT;",
+          "type": "table.column",
+          "operation": "alter",
+          "path": "public.user_pending_permissions.arfcn_dl"
+        },
+        {
+          "sql": "ALTER TABLE user_pending_permissions ALTER COLUMN arfcn_dl TYPE integer USING arfcn_dl::integer;",
+          "type": "table.column",
+          "operation": "alter",
+          "path": "public.user_pending_permissions.arfcn_dl"
+        },
+        {
+          "sql": "ALTER TABLE user_pending_permissions ALTER COLUMN arfcn_dl SET DEFAULT 0;",
+          "type": "table.column",
+          "operation": "alter",
+          "path": "public.user_pending_permissions.arfcn_dl"
+        },
+        {
+          "sql": "ALTER TABLE user_pending_permissions ALTER COLUMN priority TYPE integer USING priority::integer;",
+          "type": "table.column",
+          "operation": "alter",
+          "path": "public.user_pending_permissions.priority"
         }
       ]
     }

testdata/diff/create_table/alter_column_types/plan.sql

@@ -4,11 +4,11 @@ CREATE TYPE action_type AS ENUM (
     'rejected'
 );
 
-ALTER TABLE user_pending_permissions ALTER COLUMN id TYPE bigint;
+ALTER TABLE user_pending_permissions ALTER COLUMN id TYPE bigint USING id::bigint;
 
-ALTER TABLE user_pending_permissions ALTER COLUMN user_id TYPE bigint;
+ALTER TABLE user_pending_permissions ALTER COLUMN user_id TYPE bigint USING user_id::bigint;
 
-ALTER TABLE user_pending_permissions ALTER COLUMN object_ids_ints TYPE bigint[];
+ALTER TABLE user_pending_permissions ALTER COLUMN object_ids_ints TYPE bigint[] USING object_ids_ints::bigint[];
 
 ALTER TABLE user_pending_permissions ALTER COLUMN action TYPE action_type USING action::action_type;
 
@@ -21,3 +21,11 @@ ALTER TABLE user_pending_permissions ALTER COLUMN status SET DEFAULT 'pending'::
 ALTER TABLE user_pending_permissions ALTER COLUMN tags TYPE action_type[] USING tags::action_type[];
 
 ALTER TABLE user_pending_permissions ALTER COLUMN amount TYPE numeric(20,6);
+
+ALTER TABLE user_pending_permissions ALTER COLUMN arfcn_dl DROP DEFAULT;
+
+ALTER TABLE user_pending_permissions ALTER COLUMN arfcn_dl TYPE integer USING arfcn_dl::integer;
+
+ALTER TABLE user_pending_permissions ALTER COLUMN arfcn_dl SET DEFAULT 0;
+
+ALTER TABLE user_pending_permissions ALTER COLUMN priority TYPE integer USING priority::integer;

testdata/diff/create_table/alter_column_types/plan.txt

@@ -11,8 +11,10 @@ Tables:
   ~ user_pending_permissions
     ~ action (column)
     ~ amount (column)
+    ~ arfcn_dl (column)
     ~ id (column)
     ~ object_ids_ints (column)
+    ~ priority (column)
     ~ status (column)
     ~ tags (column)
     ~ user_id (column)
@@ -26,11 +28,11 @@ CREATE TYPE action_type AS ENUM (
     'rejected'
 );
 
-ALTER TABLE user_pending_permissions ALTER COLUMN id TYPE bigint;
+ALTER TABLE user_pending_permissions ALTER COLUMN id TYPE bigint USING id::bigint;
 
-ALTER TABLE user_pending_permissions ALTER COLUMN user_id TYPE bigint;
+ALTER TABLE user_pending_permissions ALTER COLUMN user_id TYPE bigint USING user_id::bigint;
 
-ALTER TABLE user_pending_permissions ALTER COLUMN object_ids_ints TYPE bigint[];
+ALTER TABLE user_pending_permissions ALTER COLUMN object_ids_ints TYPE bigint[] USING object_ids_ints::bigint[];
 
 ALTER TABLE user_pending_permissions ALTER COLUMN action TYPE action_type USING action::action_type;
 
@@ -43,3 +45,11 @@ ALTER TABLE user_pending_permissions ALTER COLUMN status SET DEFAULT 'pending'::
 ALTER TABLE user_pending_permissions ALTER COLUMN tags TYPE action_type[] USING tags::action_type[];
 
 ALTER TABLE user_pending_permissions ALTER COLUMN amount TYPE numeric(20,6);
+
+ALTER TABLE user_pending_permissions ALTER COLUMN arfcn_dl DROP DEFAULT;
+
+ALTER TABLE user_pending_permissions ALTER COLUMN arfcn_dl TYPE integer USING arfcn_dl::integer;
+
+ALTER TABLE user_pending_permissions ALTER COLUMN arfcn_dl SET DEFAULT 0;
+
+ALTER TABLE user_pending_permissions ALTER COLUMN priority TYPE integer USING priority::integer;