MySQL: Add support for dropping keys

dialects/mysql/src/main/kotlin/app/cash/sqldelight/dialects/mysql/grammar/MySql.bnf

@@ -219,6 +219,8 @@ alter_table_rules ::= (
   | alter_table_modify_column
   | alter_table_add_index
   | alter_table_drop_index
+  | alter_table_drop_foreign_key
+  | alter_table_drop_primary_key
   | alter_table_drop_column
   | alter_table_convert_character_set
   | row_format_clause
@@ -255,6 +257,11 @@ alter_table_add_constraint ::= ADD table_constraint
 alter_table_add_index ::= ADD [ UNIQUE ] [ INDEX | KEY ] [ {index_name} ] LP {indexed_column} ( COMMA {indexed_column} ) * RP
 
 alter_table_drop_index ::= DROP ( INDEX | KEY ) {index_name}
+alter_table_drop_foreign_key ::= DROP FOREIGN KEY {column_name} {
+  mixin = "app.cash.sqldelight.dialects.mysql.grammar.mixins.DropForeignKeyMixin"
+  pin = 2
+}
+alter_table_drop_primary_key ::= DROP PRIMARY KEY
 
 placement_clause ::= 'FIRST' | ( AFTER {column_name} )
 

dialects/mysql/src/main/kotlin/app/cash/sqldelight/dialects/mysql/grammar/mixins/DropForeignKeyMixin.kt

@@ -0,0 +1,67 @@
+package app.cash.sqldelight.dialects.mysql.grammar.mixins
+
+import app.cash.sqldelight.dialects.mysql.grammar.psi.MySqlAlterTableDropForeignKey
+import com.alecstrong.sql.psi.core.SqlAnnotationHolder
+import com.alecstrong.sql.psi.core.psi.SqlColumnDef
+import com.alecstrong.sql.psi.core.psi.SqlColumnName
+import com.alecstrong.sql.psi.core.psi.SqlCompositeElementImpl
+import com.alecstrong.sql.psi.core.psi.SqlCreateTableStmt
+import com.alecstrong.sql.psi.core.psi.SqlTableConstraint
+import com.intellij.lang.ASTNode
+import com.intellij.psi.util.childrenOfType
+import com.intellij.psi.util.parentOfType
+
+internal abstract class DropForeignKeyMixin(
+  node: ASTNode,
+) : SqlCompositeElementImpl(node),
+  MySqlAlterTableDropForeignKey {
+  override fun annotate(annotationHolder: SqlAnnotationHolder) {
+    super.annotate(annotationHolder)
+    val foreignKey = childrenOfType<SqlColumnName>().single()
+    val foundColumnDef = foreignKey.getColumnDefOrNull()
+    if (foundColumnDef == null || !foundColumnDef.isForeignKey()) {
+      annotationHolder.createErrorAnnotation(
+        foreignKey,
+        "${foreignKey.name} is not a foreign key.",
+      )
+    }
+  }
+
+  private fun SqlColumnName.getColumnDefOrNull(): SqlColumnDef? {
+    val ref = reference?.resolve() ?: return null
+    val tables = tablesAvailable(this)
+    for (table in tables) {
+      val tableDef = table.tableName.parentOfType<SqlCreateTableStmt>() ?: continue
+      for (columnDef in tableDef.columnDefList) {
+        val columnRef = columnDef.columnName.reference
+        if (columnRef != null && columnRef.resolve() == ref) {
+          return columnDef
+        }
+      }
+    }
+    return null
+  }
+
+  private fun SqlColumnDef.isForeignKey(): Boolean {
+    for (columnConstraint in columnConstraintList) {
+      if (columnConstraint.foreignKeyClause != null) {
+        return true
+      }
+    }
+    val createTableStmt: SqlCreateTableStmt? = parentOfType()
+    if (createTableStmt != null) {
+      for (tableConstraints in createTableStmt.tableConstraintList) {
+        val foreignKeyClause = tableConstraints.foreignKeyClause
+        if (foreignKeyClause != null) {
+          val columns = (foreignKeyClause.parent as SqlTableConstraint).columnNameList
+          for (column in columns) {
+            if (column.reference?.resolve() == columnName) {
+              return true
+            }
+          }
+        }
+      }
+    }
+    return false
+  }
+}

dialects/mysql/src/test/fixtures_mysql/alter-table-drop-key/1.s

@@ -0,0 +1,20 @@
+CREATE TABLE parent (
+    id INT NOT NULL,
+    PRIMARY KEY (id)
+);
+
+CREATE TABLE child (
+    id INT,
+    parent_id INT,
+    FOREIGN KEY (parent_id)  REFERENCES parent(id)
+);
+
+ALTER TABLE parent
+  DROP PRIMARY KEY;
+
+ALTER TABLE child
+  DROP FOREIGN KEY parent_id;
+
+-- Should fail, id isn't a foreign key
+ALTER TABLE child
+  DROP FOREIGN KEY id;

dialects/mysql/src/test/fixtures_mysql/alter-table-drop-key/2.s

@@ -0,0 +1,16 @@
+CREATE TABLE parent2 (
+    id INT NOT NULL,
+    PRIMARY KEY (id)
+);
+
+CREATE TABLE child2 (
+    id INT,
+    parent_id2 INT REFERENCES parent2(id)
+);
+
+ALTER TABLE child2
+  DROP FOREIGN KEY parent_id2;
+
+-- Should fail, id isn't a foreign key
+ALTER TABLE child2
+  DROP FOREIGN KEY id;

dialects/mysql/src/test/fixtures_mysql/alter-table-drop-key/failure.txt

@@ -0,0 +1,2 @@
+1.s line 20:19 - id is not a foreign key.
+2.s line 16:19 - id is not a foreign key.