fix(plpgsql-deparser): preserve ALIAS FOR declarations

__fixtures__/plpgsql-generated/generated.json

@@ -159,6 +159,9 @@
   "plpgsql_deparser_fixes-58.sql": "-- Test 58: RETURN NEXT with a variable (retvarno must be emitted as the variable name)\nCREATE FUNCTION test_return_next_var() RETURNS SETOF integer\nLANGUAGE plpgsql AS $$\nDECLARE\n  r integer;\nBEGIN\n  FOR r IN SELECT g FROM generate_series(1, 3) g LOOP\n    RETURN NEXT r;\n  END LOOP;\nEND$$",
   "plpgsql_deparser_fixes-59.sql": "-- Test 59: Top-level block with EXCEPTION clause (compiler wraps it in a synthetic outer block; must not deparse a nested BEGIN)\nCREATE FUNCTION test_toplevel_exception(a numeric, b numeric) RETURNS numeric\nLANGUAGE plpgsql AS $$\nDECLARE\n  v_result numeric;\nBEGIN\n  v_result := a / b;\n  RETURN v_result;\nEXCEPTION\n  WHEN division_by_zero THEN\n    RETURN NULL;\nEND$$",
   "plpgsql_deparser_fixes-60.sql": "-- Test 60: Explicit nested block with EXCEPTION inside a top-level block (nesting must be preserved)\nCREATE FUNCTION test_explicit_nested_exception(p_id integer) RETURNS text\nLANGUAGE plpgsql AS $$\nDECLARE\n  v_result text;\nBEGIN\n  v_result := 'unknown';\n  BEGIN\n    SELECT status INTO v_result FROM items WHERE id = p_id;\n  EXCEPTION\n    WHEN no_data_found THEN\n      v_result := 'not_found';\n  END;\n  RETURN v_result;\nEND$$",
+  "plpgsql_deparser_fixes-61.sql": "-- Test 61: ALIAS FOR a positional parameter (alias declaration must be preserved)\nCREATE FUNCTION test_alias_positional_param(integer) RETURNS integer\nLANGUAGE plpgsql AS $$\nDECLARE\n  arg ALIAS FOR $1;\nBEGIN\n  RETURN arg + 1;\nEND$$",
+  "plpgsql_deparser_fixes-62.sql": "-- Test 62: ALIAS FOR a named parameter and a local variable\nCREATE FUNCTION test_alias_named(input_value text) RETURNS text\nLANGUAGE plpgsql AS $$\nDECLARE\n  val ALIAS FOR input_value;\n  buffer text := 'x';\n  buf ALIAS FOR buffer;\nBEGIN\n  buf := buf || val;\n  RETURN buf;\nEND$$",
+  "plpgsql_deparser_fixes-63.sql": "-- Test 63: ALIAS FOR OLD/NEW in a trigger function\nCREATE FUNCTION test_alias_trigger() RETURNS trigger\nLANGUAGE plpgsql AS $$\nDECLARE\n  prior ALIAS FOR old;\n  updated ALIAS FOR new;\nBEGIN\n  updated.updated_at := now();\n  RETURN updated;\nEND$$",
   "plpgsql_control-1.sql": "--\n-- Tests for PL/pgSQL control structures\n--\n\n-- integer FOR loop\n\ndo $$\nbegin\n  -- basic case\n  for i in 1..3 loop\n    raise notice '1..3: i = %', i;\n  end loop;\n  -- with BY, end matches exactly\n  for i in 1..10 by 3 loop\n    raise notice '1..10 by 3: i = %', i;\n  end loop;\n  -- with BY, end does not match\n  for i in 1..11 by 3 loop\n    raise notice '1..11 by 3: i = %', i;\n  end loop;\n  -- zero iterations\n  for i in 1..0 by 3 loop\n    raise notice '1..0 by 3: i = %', i;\n  end loop;\n  -- REVERSE\n  for i in reverse 10..0 by 3 loop\n    raise notice 'reverse 10..0 by 3: i = %', i;\n  end loop;\n  -- potential overflow\n  for i in 2147483620..2147483647 by 10 loop\n    raise notice '2147483620..2147483647 by 10: i = %', i;\n  end loop;\n  -- potential overflow, reverse direction\n  for i in reverse -2147483620..-2147483647 by 10 loop\n    raise notice 'reverse -2147483620..-2147483647 by 10: i = %', i;\n  end loop;\nend$$",
   "plpgsql_control-2.sql": "-- BY can't be zero or negative\ndo $$\nbegin\n  for i in 1..3 by 0 loop\n    raise notice '1..3 by 0: i = %', i;\n  end loop;\nend$$",
   "plpgsql_control-3.sql": "do $$\nbegin\n  for i in 1..3 by -1 loop\n    raise notice '1..3 by -1: i = %', i;\n  end loop;\nend$$",

__fixtures__/plpgsql/plpgsql_deparser_fixes.sql

@@ -754,3 +754,35 @@ BEGIN
   END;
   RETURN v_result;
 END$$;
+
+-- Test 61: ALIAS FOR a positional parameter (alias declaration must be preserved)
+CREATE FUNCTION test_alias_positional_param(integer) RETURNS integer
+LANGUAGE plpgsql AS $$
+DECLARE
+  arg ALIAS FOR $1;
+BEGIN
+  RETURN arg + 1;
+END$$;
+
+-- Test 62: ALIAS FOR a named parameter and a local variable
+CREATE FUNCTION test_alias_named(input_value text) RETURNS text
+LANGUAGE plpgsql AS $$
+DECLARE
+  val ALIAS FOR input_value;
+  buffer text := 'x';
+  buf ALIAS FOR buffer;
+BEGIN
+  buf := buf || val;
+  RETURN buf;
+END$$;
+
+-- Test 63: ALIAS FOR OLD/NEW in a trigger function
+CREATE FUNCTION test_alias_trigger() RETURNS trigger
+LANGUAGE plpgsql AS $$
+DECLARE
+  prior ALIAS FOR old;
+  updated ALIAS FOR new;
+BEGIN
+  updated.updated_at := now();
+  RETURN updated;
+END$$;

packages/plpgsql-deparser/__tests__/__snapshots__/deparser-fixes.test.ts.snap

@@ -1,5 +1,34 @@
 // Jest Snapshot v1, https://jestjs.io/docs/snapshot-testing
 
+exports[`plpgsql-deparser bug fixes ALIAS declarations should interleave aliases with variable declarations by source order 1`] = `
+"DECLARE
+  val ALIAS FOR input_value;
+  buffer text := 'x';
+  buf ALIAS FOR buffer;
+BEGIN
+  buf := buf || val;
+  RETURN buf;
+END"
+`;
+
+exports[`plpgsql-deparser bug fixes ALIAS declarations should preserve ALIAS FOR OLD/NEW in trigger functions 1`] = `
+"DECLARE
+  prior ALIAS FOR old;
+  updated ALIAS FOR new;
+BEGIN
+  updated.updated_at := now();
+  RETURN updated;
+END"
+`;
+
+exports[`plpgsql-deparser bug fixes ALIAS declarations should preserve ALIAS FOR a positional parameter 1`] = `
+"DECLARE
+  arg ALIAS FOR $1;
+BEGIN
+  RETURN arg + 1;
+END"
+`;
+
 exports[`plpgsql-deparser bug fixes DML RETURNING ... INTO re-insertion should handle multi-column RETURNING ... INTO 1`] = `
 "DECLARE
   v_id uuid;

packages/plpgsql-deparser/__tests__/deparser-fixes.test.ts

@@ -1345,4 +1345,65 @@ END$$`;
       expect(beginCount).toBe(2);
     });
   });
+
+  describe('ALIAS declarations', () => {
+    it('should preserve ALIAS FOR a positional parameter', async () => {
+      const sql = `CREATE FUNCTION test_alias_positional_param(integer) RETURNS integer
+LANGUAGE plpgsql AS $$
+DECLARE
+  arg ALIAS FOR $1;
+BEGIN
+  RETURN arg + 1;
+END$$`;
+
+      await testUtils.expectAstMatch('alias for positional parameter', sql);
+
+      const parsed = parsePlPgSQLSync(sql) as unknown as PLpgSQLParseResult;
+      const deparsed = deparseSync(parsed);
+      expect(deparsed).toMatchSnapshot();
+      expect(deparsed).toContain('arg ALIAS FOR $1;');
+    });
+
+    it('should interleave aliases with variable declarations by source order', async () => {
+      const sql = `CREATE FUNCTION test_alias_named(input_value text) RETURNS text
+LANGUAGE plpgsql AS $$
+DECLARE
+  val ALIAS FOR input_value;
+  buffer text := 'x';
+  buf ALIAS FOR buffer;
+BEGIN
+  buf := buf || val;
+  RETURN buf;
+END$$`;
+
+      await testUtils.expectAstMatch('aliases interleaved with variables', sql);
+
+      const parsed = parsePlPgSQLSync(sql) as unknown as PLpgSQLParseResult;
+      const deparsed = deparseSync(parsed);
+      expect(deparsed).toMatchSnapshot();
+      // the alias of a local variable must come after that variable's declaration
+      expect(deparsed.indexOf('buf ALIAS FOR buffer;')).toBeGreaterThan(deparsed.indexOf('buffer text'));
+      expect(deparsed).toContain('val ALIAS FOR input_value;');
+    });
+
+    it('should preserve ALIAS FOR OLD/NEW in trigger functions', async () => {
+      const sql = `CREATE FUNCTION test_alias_trigger() RETURNS trigger
+LANGUAGE plpgsql AS $$
+DECLARE
+  prior ALIAS FOR old;
+  updated ALIAS FOR new;
+BEGIN
+  updated.updated_at := now();
+  RETURN updated;
+END$$`;
+
+      await testUtils.expectAstMatch('alias for OLD/NEW in trigger', sql);
+
+      const parsed = parsePlPgSQLSync(sql) as unknown as PLpgSQLParseResult;
+      const deparsed = deparseSync(parsed);
+      expect(deparsed).toMatchSnapshot();
+      expect(deparsed).toContain('prior ALIAS FOR old;');
+      expect(deparsed).toContain('updated ALIAS FOR new;');
+    });
+  });
 });

packages/plpgsql-deparser/src/plpgsql-deparser.ts

@@ -17,6 +17,7 @@ import {
   PLpgSQLFunctionNode,
   PLpgSQL_function,
   PLpgSQLDatum,
+  PLpgSQLAliasNode,
   PLpgSQL_var,
   PLpgSQL_rec,
   PLpgSQL_row,
@@ -213,7 +214,8 @@ export class PLpgSQLDeparser {
       context,
       loopVarLinenos,
       undefined,  // includedIndices - not used for top-level
-      nestedDatumIndices  // excludedIndices - exclude datums that belong to nested blocks
+      nestedDatumIndices,  // excludedIndices - exclude datums that belong to nested blocks
+      func.aliases
     );
     if (declareSection) {
       parts.push(declareSection);
@@ -631,7 +633,8 @@ export class PLpgSQLDeparser {
     context: PLpgSQLDeparserContext,
     loopVarLinenos: Set<number> = new Set(),
     includedIndices?: Set<number>,
-    excludedIndices?: Set<number>
+    excludedIndices?: Set<number>,
+    aliases?: PLpgSQLAliasNode[]
   ): string {
     if (!datums || datums.length === 0) {
       return '';
@@ -698,20 +701,42 @@ export class PLpgSQLDeparser {
       return false;
     });
 
-    if (localVars.length === 0) {
-      return '';
+    // ALIAS declarations bind a new name to an existing datum (e.g. `arg ALIAS FOR $1`).
+    // They are interleaved with variable declarations by source lineno so an alias
+    // targeting a local variable is emitted after that variable's declaration.
+    // On equal linenos, variables sort before aliases so a same-line alias
+    // targeting a variable still follows its declaration.
+    const decls: { lineno: number; order: number; text: string }[] = [];
+    for (const alias of aliases ?? []) {
+      const { name, varno, lineno } = alias.PLpgSQL_alias;
+      const targetName = this.getVarName(varno, context);
+      decls.push({ lineno: lineno ?? 0, order: 1, text: `${name} ${this.keyword('ALIAS FOR')} ${targetName}` });
     }
 
-    const kw = this.keyword;
-    const parts: string[] = [kw('DECLARE')];
-
     for (const datum of localVars) {
       const varDecl = this.deparseDatum(datum, context);
       if (varDecl) {
-        parts.push(this.indent(varDecl + ';', context.indentLevel + 1));
+        const lineno =
+          ('PLpgSQL_var' in datum ? datum.PLpgSQL_var.lineno : undefined) ??
+          ('PLpgSQL_rec' in datum ? datum.PLpgSQL_rec.lineno : undefined) ??
+          0;
+        decls.push({ lineno, order: 0, text: varDecl });
       }
     }
 
+    if (decls.length === 0) {
+      return '';
+    }
+
+    decls.sort((a, b) => a.lineno - b.lineno || a.order - b.order);
+
+    const kw = this.keyword;
+    const parts: string[] = [kw('DECLARE')];
+
+    for (const decl of decls) {
+      parts.push(this.indent(decl.text + ';', context.indentLevel + 1));
+    }
+
     return parts.join(this.options.newline);
   }
 

packages/plpgsql-deparser/src/types.ts

@@ -18,6 +18,18 @@ export interface PLpgSQL_function {
   datums?: PLpgSQLDatum[];
   action?: PLpgSQLStmtNode;
   out_param_varno?: number;
+  aliases?: PLpgSQLAliasNode[];
+}
+
+export type PLpgSQLAliasNode = {
+  PLpgSQL_alias: PLpgSQL_alias;
+};
+
+/** An ALIAS declaration (e.g. `arg ALIAS FOR $1`): a name bound to an existing datum */
+export interface PLpgSQL_alias {
+  name: string;
+  varno: number;
+  lineno?: number;
 }
 
 export type PLpgSQLDatum =