Fix behavior of SQLColumn when "*" is specified as a column name (#181)

Fix behavior of SQLColumn when "*" is specified as a column name (this behavior belonged in SQLColumn, not in SQLUnqualifiedColumnListBuilder) and add tests. Fixes #180.

Sources/SQLKit/Builders/Prototypes/SQLUnqualifiedColumnListBuilder.swift

@@ -14,7 +14,7 @@ extension SQLUnqualifiedColumnListBuilder {
     @inlinable
     @discardableResult
     public func column(_ column: String) -> Self {
-        self.column(column == "*" ? SQLLiteral.all : SQLColumn(column))
+        self.column(SQLColumn(column))
     }
 
     /// Specify a single column to be included in the list of columns for the query.
@@ -36,7 +36,7 @@ extension SQLUnqualifiedColumnListBuilder {
     @inlinable
     @discardableResult
     public func columns(_ columns: [String]) -> Self {
-        self.columns(columns.map { $0 == "*" ? SQLLiteral.all as any SQLExpression : SQLColumn($0) })
+        self.columns(columns.map { SQLColumn($0) })
     }
 
     /// Specify mutiple columns to be included in the list of columns for the query.

Sources/SQLKit/Expressions/Basics/SQLColumn.swift

@@ -1,18 +1,26 @@
 /// An expression representing an optionally table-qualified column in an SQL table.
 public struct SQLColumn: SQLExpression {
-    /// The column name, usually an ``SQLIdentifier``.
+    /// The column name.
+    ///
+    /// Usually an ``SQLIdentifier``.
     public var name: any SQLExpression
 
-    /// If specified, the table to which the column belongs. Usually an ``SQLIdentifier`` when not `nil`.
+    /// If specified, the table to which the column belongs.
+    ///
+    /// Usually an ``SQLIdentifier`` or ``SQLQualifiedTable`` when not `nil`.
     public var table: (any SQLExpression)?
 
     /// Create an ``SQLColumn`` from a name and optional table name.
+    ///
+    /// A column name of `*` is treated as ``SQLLiteral/all`` rather than as an identifier. To specify a column whose
+    /// actual name consists of a sole asterisk (probably not a good idea to have one of those in the first place),
+    /// use ``init(_:table:)-77d24`` and `SQLIdentifier("*")`.
     @inlinable
     public init(_ name: String, table: String? = nil) {
-        self.init(SQLIdentifier(name), table: table.flatMap(SQLIdentifier.init(_:)))
+        self.init(name == "*" ? SQLLiteral.all : SQLIdentifier(name), table: table.flatMap(SQLIdentifier.init(_:)))
     }
 
-    /// Create an ``SQLColumn`` from an identifier and optional table identifier.
+    /// Create an ``SQLColumn`` from an identifier and optional table expression.
     @inlinable
     public init(_ name: any SQLExpression, table: (any SQLExpression)? = nil) {
         self.name = name

Tests/SQLKitTests/BasicQueryTests.swift

@@ -10,16 +10,22 @@ final class BasicQueryTests: XCTestCase {
 
     // MARK: Select
 
-    func testSelect_unqualifiedColums() {
+    func testSelect_unqualifiedColumns() {
         XCTAssertSerialization(
             of: self.db.select()
+                .column("*")
                 .column("name")
+                .column(SQLLiteral.all)
                 .column(SQLIdentifier("name"))
+                .columns("*")
                 .columns("name")
+                .columns(["*"])
                 .columns(["name"])
+                .columns(SQLLiteral.all)
                 .columns(SQLIdentifier("name"))
+                .columns([SQLLiteral.all])
                 .columns([SQLIdentifier("name")]),
-            is: "SELECT ``name``, ``name``, ``name``, ``name``, ``name``, ``name``"
+            is: "SELECT *, ``name``, *, ``name``, *, ``name``, *, ``name``, *, ``name``, *, ``name``"
         )
     }
 

Tests/SQLKitTests/SQLExpressionTests.swift

@@ -265,4 +265,13 @@ final class SQLExpressionTests: XCTestCase {
         self.db._dialect.literalStringQuote = SQLQueryString("~")
         XCTAssertSerialization(of: self.db.raw("\(ident: "hello") \(literal: "there")"), is: "_hello_ ~there~")
     }
+
+    func testColumns() {
+        XCTAssertSerialization(of: self.db.raw("\(SQLColumn("*"))"), is: "*")
+        XCTAssertSerialization(of: self.db.raw("\(SQLColumn(SQLIdentifier("*")))"), is: "``*``")
+        XCTAssertSerialization(of: self.db.raw("\(SQLColumn(SQLLiteral.all))"), is: "*")
+        XCTAssertSerialization(of: self.db.raw("\(SQLColumn("*", table: "foo"))"), is: "``foo``.*")
+        XCTAssertSerialization(of: self.db.raw("\(SQLColumn(SQLIdentifier("*"), table: SQLIdentifier("foo")))"), is: "``foo``.``*``")
+        XCTAssertSerialization(of: self.db.raw("\(SQLColumn(SQLLiteral.all, table: SQLIdentifier("foo")))"), is: "``foo``.*")
+    }
 }