SGA-11783 Address review feedback for SHOW CHARSET

Improves the initial `SHOW CHARSET` implementation by:
- Using a named struct for the AST node
- Adding AST assertion to the parser test
- Improving code comments

Author: etgarperets

src/ast/mod.rs

@@ -3705,19 +3705,11 @@ pub enum Statement {
         show_options: ShowStatementOptions,
     },
     // ```sql
-    // SHOW {CHARACTER SET | CHARSET} [like_or_where]
+    // SHOW {CHARACTER SET | CHARSET}
     // ```
-    // where:
-    // like_or_where: {
-    //     LIKE 'pattern'
-    //   | WHERE expr
-    // }
-    // MySQL specific statement
+    // [MySQL]:
     // <https://dev.mysql.com/doc/refman/8.4/en/show.html#:~:text=SHOW%20%7BCHARACTER%20SET%20%7C%20CHARSET%7D%20%5Blike_or_where%5D>
-    ShowCharset {
-        is_shorthand: bool,
-        filter: Option<ShowStatementFilter>,
-    },
+    ShowCharset(ShowCharset),
     /// ```sql
     /// SHOW OBJECTS LIKE 'line%' IN mydb.public
     /// ```
@@ -5688,21 +5680,7 @@ impl fmt::Display for Statement {
                 }
                 Ok(())
             }
-            Statement::ShowCharset {
-                is_shorthand,
-                filter,
-            } => {
-                write!(f, "SHOW")?;
-                if *is_shorthand {
-                    write!(f, " CHARSET")?;
-                } else {
-                    write!(f, " CHARACTER SET")?;
-                }
-                if filter.is_some() {
-                    write!(f, " {}", filter.as_ref().unwrap())?;
-                }
-                Ok(())
-            }
+            Statement::ShowCharset(show_stm) => show_stm.fmt(f),
             Statement::StartTransaction {
                 modes,
                 begin: syntax_begin,
@@ -9821,6 +9799,32 @@ impl fmt::Display for ShowStatementIn {
     }
 }
 
+/// A Show Charset statement
+#[derive(Debug, Clone, PartialEq, PartialOrd, Eq, Ord, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+#[cfg_attr(feature = "visitor", derive(Visit, VisitMut))]
+pub struct ShowCharset {
+    /// The statement can be written as SHOW CHARSET or SHOW CHARACTER SET
+    /// true means CHARSET was used and false means CHARACTER SET was used
+    pub is_shorthand: bool,
+    pub filter: Option<ShowStatementFilter>,
+}
+
+impl fmt::Display for ShowCharset {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "SHOW")?;
+        if self.is_shorthand {
+            write!(f, " CHARSET")?;
+        } else {
+            write!(f, " CHARACTER SET")?;
+        }
+        if self.filter.is_some() {
+            write!(f, " {}", self.filter.as_ref().unwrap())?;
+        }
+        Ok(())
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, PartialOrd, Eq, Ord, Hash)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[cfg_attr(feature = "visitor", derive(Visit, VisitMut))]

src/parser/mod.rs

@@ -12518,10 +12518,10 @@ impl<'a> Parser<'a> {
 
     fn parse_show_charset(&mut self, is_shorthand: bool) -> Result<Statement, ParserError> {
         // parse one of keywords
-        Ok(Statement::ShowCharset {
+        Ok(Statement::ShowCharset(ShowCharset {
             is_shorthand,
             filter: self.parse_show_statement_filter()?,
-        })
+        }))
     }
 
     fn parse_show_databases(&mut self, terse: bool) -> Result<Statement, ParserError> {

tests/sqlparser_mysql.rs

@@ -4146,8 +4146,15 @@ fn parse_json_member_of() {
 
 #[test]
 fn parse_show_charset() {
-    let _ = mysql().verified_stmt("SHOW CHARACTER SET");
-    let _ = mysql().verified_stmt("SHOW CHARACTER SET LIKE 'utf8mb4%'");
-    let _ = mysql().verified_stmt("SHOW CHARSET WHERE charset = 'utf8mb4%'");
-    let _ = mysql().verified_stmt("SHOW CHARSET LIKE 'utf8mb4%'");
+    let res = mysql().verified_stmt("SHOW CHARACTER SET");
+    assert_eq!(
+        res,
+        Statement::ShowCharset(ShowCharset {
+            is_shorthand: false,
+            filter: None
+        })
+    );
+    mysql().verified_stmt("SHOW CHARACTER SET LIKE 'utf8mb4%'");
+    mysql().verified_stmt("SHOW CHARSET WHERE charset = 'utf8mb4%'");
+    mysql().verified_stmt("SHOW CHARSET LIKE 'utf8mb4%'");
 }