ide: remove redundant alias

crates/squawk_ide/src/code_actions.rs

@@ -1,4 +1,4 @@
-use rowan::TextSize;
+use rowan::{TextRange, TextSize};
 use squawk_linter::Edit;
 use squawk_syntax::{
     SyntaxKind,
@@ -9,6 +9,7 @@ use crate::{
     column_name::ColumnName,
     offsets::token_from_offset,
     quote::{quote_column_alias, unquote_ident},
+    symbols::Name,
 };
 
 #[derive(Debug, Clone)]
@@ -34,6 +35,7 @@ pub fn code_actions(file: ast::SourceFile, offset: TextSize) -> Option<Vec<CodeA
     quote_identifier(&mut actions, &file, offset);
     unquote_identifier(&mut actions, &file, offset);
     add_explicit_alias(&mut actions, &file, offset);
+    remove_redundant_alias(&mut actions, &file, offset);
     Some(actions)
 }
 
@@ -395,6 +397,45 @@ fn add_explicit_alias(
     Some(())
 }
 
+fn remove_redundant_alias(
+    actions: &mut Vec<CodeAction>,
+    file: &ast::SourceFile,
+    offset: TextSize,
+) -> Option<()> {
+    let token = token_from_offset(file, offset)?;
+    let target = token.parent_ancestors().find_map(ast::Target::cast)?;
+
+    let as_name = target.as_name()?;
+    let alias_name = as_name.name()?;
+
+    let (inferred_column, _) = ColumnName::inferred_from_target(target.clone())?;
+    let inferred_column_alias = inferred_column.to_string()?;
+
+    let alias = alias_name.syntax().text().to_string();
+
+    if Name::new(alias) != Name::new(inferred_column_alias) {
+        return None;
+    }
+
+    // TODO:
+    // This lets use remove any whitespace so we don't end up with:
+    //   select x as x, b from t;
+    // becoming
+    //   select x , b from t;
+    // but we probably want a better way to express this.
+    // Maybe a "Remove preceding whitespace" style option for edits.
+    let expr_end = target.expr()?.syntax().text_range().end();
+    let alias_end = as_name.syntax().text_range().end();
+
+    actions.push(CodeAction {
+        title: "Remove redundant alias".to_owned(),
+        edits: vec![Edit::delete(TextRange::new(expr_end, alias_end))],
+        kind: ActionKind::QuickFix,
+    });
+
+    Some(())
+}
+
 #[cfg(test)]
 mod test {
     use super::*;
@@ -1045,4 +1086,65 @@ mod test {
             @r#"select 'foo' as "?column?" from t;"#
         );
     }
+
+    #[test]
+    fn remove_redundant_alias_simple() {
+        assert_snapshot!(apply_code_action(
+            remove_redundant_alias,
+            "select col_name as col_na$0me from t;"),
+            @"select col_name from t;"
+        );
+    }
+
+    #[test]
+    fn remove_redundant_alias_quoted() {
+        assert_snapshot!(apply_code_action(
+            remove_redundant_alias,
+            r#"select "x"$0 as x from t;"#),
+            @r#"select "x" from t;"#
+        );
+    }
+
+    #[test]
+    fn remove_redundant_alias_case_insensitive() {
+        assert_snapshot!(apply_code_action(
+            remove_redundant_alias,
+            "select col_name$0 as COL_NAME from t;"),
+            @"select col_name from t;"
+        );
+    }
+
+    #[test]
+    fn remove_redundant_alias_function() {
+        assert_snapshot!(apply_code_action(
+            remove_redundant_alias,
+            "select count(*)$0 as count from t;"),
+            @"select count(*) from t;"
+        );
+    }
+
+    #[test]
+    fn remove_redundant_alias_field_expr() {
+        assert_snapshot!(apply_code_action(
+            remove_redundant_alias,
+            "select t.col$0umn as column from t;"),
+            @"select t.column from t;"
+        );
+    }
+
+    #[test]
+    fn remove_redundant_alias_not_applicable_different_name() {
+        assert!(code_action_not_applicable(
+            remove_redundant_alias,
+            "select col_name$0 as foo from t;"
+        ));
+    }
+
+    #[test]
+    fn remove_redundant_alias_not_applicable_no_alias() {
+        assert!(code_action_not_applicable(
+            remove_redundant_alias,
+            "select col_name$0 from t;"
+        ));
+    }
 }

crates/squawk_ide/src/column_name.rs

@@ -3,13 +3,7 @@ use squawk_syntax::{
     ast::{self, AstNode},
 };
 
-fn normalize_identifier(text: &str) -> String {
-    if text.starts_with('"') && text.ends_with('"') {
-        text[1..text.len() - 1].to_string()
-    } else {
-        text.to_lowercase()
-    }
-}
+use crate::quote::normalize_identifier;
 
 #[derive(Clone, Debug, PartialEq)]
 pub(crate) enum ColumnName {
@@ -30,14 +24,21 @@ pub(crate) enum ColumnName {
 }
 
 impl ColumnName {
+    // Get the alias, otherwise infer the column name.
     pub(crate) fn from_target(target: ast::Target) -> Option<(ColumnName, SyntaxNode)> {
         if let Some(as_name) = target.as_name()
             && let Some(name_node) = as_name.name()
         {
             let text = name_node.text();
             let normalized = normalize_identifier(&text);
             return Some((ColumnName::Column(normalized), name_node.syntax().clone()));
-        } else if let Some(expr) = target.expr()
+        }
+        Self::inferred_from_target(target)
+    }
+
+    // Ignore any aliases, just infer the what the column name.
+    pub(crate) fn inferred_from_target(target: ast::Target) -> Option<(ColumnName, SyntaxNode)> {
+        if let Some(expr) = target.expr()
             && let Some(name) = name_from_expr(expr, false)
         {
             return Some(name);

crates/squawk_ide/src/quote.rs

@@ -77,6 +77,14 @@ pub(crate) fn is_reserved_word(text: &str) -> bool {
         .is_ok()
 }
 
+pub(crate) fn normalize_identifier(text: &str) -> String {
+    if text.starts_with('"') && text.ends_with('"') && text.len() >= 2 {
+        text[1..text.len() - 1].to_string()
+    } else {
+        text.to_lowercase()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

crates/squawk_ide/src/symbols.rs

@@ -3,6 +3,8 @@ use smol_str::SmolStr;
 use squawk_syntax::SyntaxNodePtr;
 use std::fmt;
 
+use crate::quote::normalize_identifier;
+
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub(crate) struct Name(pub(crate) SmolStr);
 
@@ -25,7 +27,7 @@ impl Name {
     pub(crate) fn new(text: impl Into<SmolStr>) -> Self {
         let text = text.into();
         let normalized = normalize_identifier(&text);
-        Name(normalized)
+        Name(normalized.into())
     }
 }
 
@@ -35,14 +37,6 @@ impl fmt::Display for Name {
     }
 }
 
-fn normalize_identifier(text: &str) -> SmolStr {
-    if text.starts_with('"') && text.ends_with('"') && text.len() >= 2 {
-        text[1..text.len() - 1].into()
-    } else {
-        text.to_lowercase().into()
-    }
-}
-
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
 pub(crate) enum SymbolKind {
     Table,
@@ -59,3 +53,17 @@ pub(crate) struct Symbol {
 }
 
 pub(crate) type SymbolId = Idx<Symbol>;
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    #[test]
+    fn name_case_insensitive_compare() {
+        assert_eq!(Name::new("foo"), Name::new("FOO"));
+    }
+
+    #[test]
+    fn name_quote_comparing() {
+        assert_eq!(Name::new(r#""foo""#), Name::new("foo"));
+    }
+}