Merge pull request #1296 from DougGregor/freestanding-expansion-as-expr-again

[Parser] Go back to parsing macro expansions as expressions where possible

Author: DougGregor

CodeGeneration/Sources/SyntaxSupport/gyb_generated/ExprNodes.swift

@@ -1160,7 +1160,7 @@ public let EXPR_NODES: [Node] = [
        ]),
 
   Node(name: "MacroExpansionExpr",
-       nameForDiagnostics: "macro expansion expression",
+       nameForDiagnostics: "macro expansion",
        kind: "Expr",
        traits: [
          "FreestandingMacroExpansion"

Sources/SwiftParser/Declarations.swift

@@ -32,13 +32,12 @@ extension TokenConsumer {
   mutating func atStartOfDeclaration(
     isAtTopLevel: Bool = false,
     allowInitDecl: Bool = true,
-    allowRecovery: Bool = false,
-    preferPoundAsExpression: Bool = false
+    allowRecovery: Bool = false
   ) -> Bool {
     if self.at(anyIn: PoundDeclarationStart.self) != nil {
-      // If we are in a context where we prefer # to be an expression,
-      // treat it as one if it's not at the start of the line.
-      if preferPoundAsExpression && self.at(.pound) && !self.currentToken.isAtStartOfLine {
+      // Don't treat freestanding macro expansions as declarations. They'll be
+      // parsed as expressions.
+      if self.at(.pound) {
         return false
       }
 

Sources/SwiftParser/Statements.swift

@@ -959,7 +959,7 @@ extension Parser {
       .poundIfKeyword, .poundEndifKeyword, .poundElseKeyword,
       .poundElseifKeyword,
     ])
-      && !self.atStartOfStatement() && !self.atStartOfDeclaration(preferPoundAsExpression: true)
+      && !self.atStartOfStatement() && !self.atStartOfDeclaration()
     {
       let parsedExpr = self.parseExpression()
       if hasMisplacedTry && !parsedExpr.is(RawTryExprSyntax.self) {

Sources/SwiftSyntax/generated/Misc.swift

@@ -1108,7 +1108,7 @@ extension SyntaxKind {
     case .macroExpansionDecl: 
       return "macro expansion"
     case .macroExpansionExpr: 
-      return "macro expansion expression"
+      return "macro expansion"
     case .matchingPatternCondition: 
       return "pattern matching"
     case .memberAccessExpr: 

Sources/SwiftSyntaxMacros/MacroProtocols/CodeItemMacro.swift

@@ -13,8 +13,11 @@ import SwiftSyntax
 public protocol CodeItemMacro: FreestandingMacro {
   /// Expand a macro described by the given freestanding macro expansion
   /// declaration within the given context to produce a set of declarations.
-  static func expansion<Context: MacroExpansionContext>(
-    of node: MacroExpansionDeclSyntax,
+  static func expansion<
+    Node: FreestandingMacroExpansionSyntax,
+    Context: MacroExpansionContext
+  >(
+    of node: Node,
     in context: Context
   ) throws -> [CodeBlockItemSyntax]
 }

Sources/SwiftSyntaxMacros/MacroProtocols/DeclarationMacro.swift

@@ -14,9 +14,10 @@ public protocol DeclarationMacro: FreestandingMacro {
   /// Expand a macro described by the given freestanding macro expansion
   /// declaration within the given context to produce a set of declarations.
   static func expansion<
+    Node: FreestandingMacroExpansionSyntax,
     Context: MacroExpansionContext
   >(
-    of node: MacroExpansionDeclSyntax,
+    of node: Node,
     in context: Context
   ) throws -> [DeclSyntax]
 }

Sources/SwiftSyntaxMacros/MacroProtocols/ExpressionMacro.swift

@@ -14,7 +14,7 @@ import SwiftSyntax
 
 /// Describes a macro that is explicitly expanded as an expression.
 public protocol ExpressionMacro: FreestandingMacro {
-  /// Expand a macro described by the given macro expansion expression
+  /// Expand a macro described by the given freestanding macro expansion
   /// within the given context to produce a replacement expression.
   static func expansion<
     Node: FreestandingMacroExpansionSyntax,

Sources/SwiftSyntaxMacros/MacroSystem.swift

@@ -127,14 +127,14 @@ class MacroApplication<Context: MacroExpansionContext>: SyntaxRewriter {
     for item in node {
       // Expand declaration macros that were parsed as macro expansion
       // expressions in this context.
-      if case let .decl(declItem) = item.item,
-        let declExpansion = declItem.as(MacroExpansionDeclSyntax.self),
-        let macro = macroSystem.macros[declExpansion.macro.text]
+      if case let .expr(exprItem) = item.item,
+        let exprExpansion = exprItem.as(MacroExpansionExprSyntax.self),
+        let macro = macroSystem.macros[exprExpansion.macro.text]
       {
         do {
           if let macro = macro as? DeclarationMacro.Type {
             let expandedItemList = try macro.expansion(
-              of: declExpansion,
+              of: exprExpansion,
               in: context
             )
             newItems.append(
@@ -144,7 +144,7 @@ class MacroApplication<Context: MacroExpansionContext>: SyntaxRewriter {
             )
           } else if let macro = macro as? ExpressionMacro.Type {
             let expandedExpr = try macro.expansion(
-              of: declExpansion,
+              of: exprExpansion,
               in: context
             )
             newItems.append(CodeBlockItemSyntax(item: .init(expandedExpr)))

Tests/SwiftParserTest/ExpressionTests.swift

@@ -896,6 +896,10 @@ final class ExpressionTests: XCTestCase {
   }
 
   func testMacroExpansionExpression() {
+    AssertParse(
+      #"#file == $0.path"#
+    )
+
     AssertParse(
       #"let a = #embed("filename.txt")"#
     )

Tests/SwiftParserTest/translated/ObjectLiteralsTests.swift

@@ -21,7 +21,7 @@ final class ObjectLiteralsTests: XCTestCase {
       let _ = [#Color(colorLiteralRed: red, green: green, blue: blue, alpha: alpha)#1️⃣]
       """,
       diagnostics: [
-        DiagnosticSpec(locationMarker: "1️⃣", message: "expected identifier in macro expansion expression")
+        DiagnosticSpec(locationMarker: "1️⃣", message: "expected identifier in macro expansion")
       ]
     )
   }
@@ -32,7 +32,7 @@ final class ObjectLiteralsTests: XCTestCase {
       let _ = [#Image(imageLiteral: localResourceNameAsString)#1️⃣]
       """,
       diagnostics: [
-        DiagnosticSpec(locationMarker: "1️⃣", message: "expected identifier in macro expansion expression")
+        DiagnosticSpec(locationMarker: "1️⃣", message: "expected identifier in macro expansion")
       ]
     )
   }
@@ -43,7 +43,7 @@ final class ObjectLiteralsTests: XCTestCase {
       let _ = [#FileReference(fileReferenceLiteral: localResourceNameAsString)#1️⃣]
       """,
       diagnostics: [
-        DiagnosticSpec(locationMarker: "1️⃣", message: "expected identifier in macro expansion expression")
+        DiagnosticSpec(locationMarker: "1️⃣", message: "expected identifier in macro expansion")
       ]
     )
   }
@@ -102,8 +102,8 @@ final class ObjectLiteralsTests: XCTestCase {
       let _ = [#1️⃣#2️⃣]
       """,
       diagnostics: [
-        DiagnosticSpec(locationMarker: "1️⃣", message: "expected identifier in macro expansion expression"),
-        DiagnosticSpec(locationMarker: "2️⃣", message: "expected identifier in macro expansion expression"),
+        DiagnosticSpec(locationMarker: "1️⃣", message: "expected identifier in macro expansion"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "expected identifier in macro expansion"),
       ]
     )
   }
@@ -125,7 +125,7 @@ final class ObjectLiteralsTests: XCTestCase {
       let _ = [1️⃣#Color(red: 1, green: 1, blue: 1)#2️⃣3️⃣
       """,
       diagnostics: [
-        DiagnosticSpec(locationMarker: "2️⃣", message: "expected identifier in macro expansion expression"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "expected identifier in macro expansion"),
         DiagnosticSpec(locationMarker: "3️⃣", message: "expected ']' to end array"),
       ]
     )
@@ -137,7 +137,7 @@ final class ObjectLiteralsTests: XCTestCase {
       let _ = [#Color(withRed: 1, green: 1, whatever: 2)#1️⃣]
       """,
       diagnostics: [
-        DiagnosticSpec(locationMarker: "1️⃣", message: "expected identifier in macro expansion expression")
+        DiagnosticSpec(locationMarker: "1️⃣", message: "expected identifier in macro expansion")
       ]
     )
   }