From 678ca8d33b59b2d928d622a93e3649d1f3b4a0db Mon Sep 17 00:00:00 2001
From: "Levy A." <levyddsa@gmail.com>
Date: Wed, 27 Aug 2025 15:45:03 -0300
Subject: [PATCH] feat(parser): add `ALTER COLUMN`

---
 core/translate/alter.rs |  3 +++
 parser/src/ast.rs       |  2 ++
 parser/src/ast/fmt.rs   |  7 +++++++
 parser/src/lexer.rs     |  2 +-
 parser/src/parser.rs    | 36 ++++++++++++++++++++++++++++++++++--
 5 files changed, 47 insertions(+), 3 deletions(-)

diff --git a/core/translate/alter.rs b/core/translate/alter.rs
index 0990e90ac..3699fdce8 100644
--- a/core/translate/alter.rs
+++ b/core/translate/alter.rs
@@ -411,5 +411,8 @@ pub fn translate_alter_table(
 
             program
         }
+        ast::AlterTableBody::AlterColumn { .. } => {
+            todo!("`ALTER COLUMN` not implemented")
+        }
     })
 }
diff --git a/parser/src/ast.rs b/parser/src/ast.rs
index a0640aac5..d1b429a1e 100644
--- a/parser/src/ast.rs
+++ b/parser/src/ast.rs
@@ -982,6 +982,8 @@ pub enum AlterTableBody {
     RenameTo(Name),
     /// `ADD COLUMN`
     AddColumn(ColumnDefinition), // TODO distinction between ADD and ADD COLUMN
+    /// `ALTER COLUMN`
+    AlterColumn { old: Name, new: ColumnDefinition },
     /// `RENAME COLUMN`
     RenameColumn {
         /// old name
diff --git a/parser/src/ast/fmt.rs b/parser/src/ast/fmt.rs
index ee0b6716e..0e46cb680 100644
--- a/parser/src/ast/fmt.rs
+++ b/parser/src/ast/fmt.rs
@@ -1409,6 +1409,13 @@ impl ToTokens for AlterTableBody {
                 s.append(TK_COLUMNKW, None)?;
                 def.to_tokens_with_context(s, context)
             }
+            Self::AlterColumn { old, new } => {
+                s.append(TK_ALTER, None)?;
+                s.append(TK_COLUMNKW, None)?;
+                old.to_tokens_with_context(s, context)?;
+                s.append(TK_TO, None)?;
+                new.to_tokens_with_context(s, context)
+            }
             Self::RenameColumn { old, new } => {
                 s.append(TK_RENAME, None)?;
                 s.append(TK_COLUMNKW, None)?;
diff --git a/parser/src/lexer.rs b/parser/src/lexer.rs
index 1ea608e14..70240a42d 100644
--- a/parser/src/lexer.rs
+++ b/parser/src/lexer.rs
@@ -17,7 +17,7 @@ pub fn is_identifier_continue(b: u8) -> bool {
         || b > b'\x7F'
 }
 
-#[derive(Clone, PartialEq, Eq)] // do not derive Copy for Token, just use .clone() when needed
+#[derive(Clone, PartialEq, Eq, Debug)] // do not derive Copy for Token, just use .clone() when needed
 pub struct Token<'a> {
     pub value: &'a [u8],
     pub token_type: Option<TokenType>, // None means Token is whitespaces or comments
diff --git a/parser/src/parser.rs b/parser/src/parser.rs
index 124058fc9..4de88dbd7 100644
--- a/parser/src/parser.rs
+++ b/parser/src/parser.rs
@@ -425,7 +425,8 @@ impl<'a> Parser<'a> {
                 }
                 TK_COLUMNKW => {
                     let prev_tt = self.current_token.token_type.unwrap_or(TK_EOF);
-                    let can_be_columnkw = matches!(prev_tt, TK_ADD | TK_RENAME | TK_DROP);
+                    let can_be_columnkw =
+                        matches!(prev_tt, TK_ADD | TK_RENAME | TK_DROP | TK_ALTER);
 
                     if !can_be_columnkw {
                         tok.token_type = Some(TK_ID);
@@ -3437,7 +3438,7 @@ impl<'a> Parser<'a> {
         eat_assert!(self, TK_ALTER);
         eat_expect!(self, TK_TABLE);
         let tbl_name = self.parse_fullname(false)?;
-        let tok = eat_expect!(self, TK_ADD, TK_DROP, TK_RENAME);
+        let tok = eat_expect!(self, TK_ADD, TK_DROP, TK_RENAME, TK_ALTER);
 
         match tok.token_type.unwrap() {
             TK_ADD => {
@@ -3488,6 +3489,19 @@ impl<'a> Parser<'a> {
                     }))
                 }
             }
+            TK_ALTER => {
+                eat_expect!(self, TK_COLUMNKW);
+                let col_name = self.parse_nm()?;
+
+                eat_expect!(self, TK_TO);
+
+                let new = self.parse_column_definition(true)?;
+
+                Ok(Stmt::AlterTable(AlterTable {
+                    name: tbl_name,
+                    body: AlterTableBody::AlterColumn { old: col_name, new },
+                }))
+            }
             _ => unreachable!(),
         }
     }
@@ -9855,6 +9869,24 @@ mod tests {
                     }),
                 }))],
             ),
+            (
+                b"ALTER TABLE foo ALTER COLUMN bar TO baz INTEGER".as_slice(),
+                vec![Cmd::Stmt(Stmt::AlterTable (AlterTable {
+                    name: QualifiedName { db_name: None, name: Name::Ident("foo".to_owned()), alias: None },
+                    body: AlterTableBody::AlterColumn {
+                        old: Name::Ident("bar".to_owned()),
+                        new: ColumnDefinition {
+                            col_name: Name::Ident("baz".to_owned()),
+                            col_type: Some(Type {
+                                name: "INTEGER".to_owned(),
+                                size: None,
+                            }),
+                            constraints: vec![],
+                        },
+
+                    },
+                }))],
+            ),
             // parse create index
             (
                 b"CREATE INDEX idx_foo ON foo (bar)".as_slice(),