[TypeCheckMacros] Never associate MacroExpansionExpr with a closure

The closures are type-checked after macros are expanded
which means that macro cannot reference any declarations
from inner or outer closures as its arguments.

For example:

`_: (Int) -> Void = { x in { @macro(x) in ... }() }`

`x` is not going to be type-checked at macro expansion
time and cannot be referenced by `@Macro`.

Let's walk up declaration contexts until we find first
non-closure one. This means that we can support a local
declaration that is defined inside of a closure because
they are separately checked after outer ones are already
processed.

Author: xedin

lib/Sema/TypeCheckMacros.cpp

@@ -2257,6 +2257,28 @@ ConcreteDeclRef ResolveMacroRequest::evaluate(Evaluator &evaluator,
           dc, expansion->getExpansionInfo(), roles);
     }
   } else {
+    if (isa<ClosureExpr>(dc) && roles.contains(MacroRole::Body)) {
+      // The closures are type-checked after macros are expanded
+      // which means that macro cannot reference any declarations
+      // from inner or outer closures as its arguments.
+      //
+      // For example:
+      // `_: (Int) -> Void = { x in { @Macro(x) in ... }() }`
+      //
+      // `x` is not going to be type-checked at macro expansion
+      // time and cannot be referenced by `@Macro`.
+      //
+      // Let's walk up declaration contexts until we find first
+      // non-closure one. This means that we can support a local
+      // declaration that is defined inside of a closure because
+      // they are separately checked after outer ones are already
+      // processed.
+      while ((dc = dc->getParent())) {
+        if (!isa<AbstractClosureExpr>(dc))
+          break;
+      }
+    }
+
     SourceRange genericArgsRange = macroRef.getGenericArgsRange();
     macroExpansion = MacroExpansionExpr::create(
       dc, macroRef.getSigilLoc(),

test/Macros/start_task.swift

@@ -15,14 +15,107 @@ func sync() {
 }
 
 func takeClosure(
-  _ closure: @escaping @Sendable () -> Void
+  _ closure: @escaping @Sendable () -> Void,
+  v: Int = 42
 ) {
   closure()
 }
 
+func multipleClosures(
+  a: @escaping @Sendable () -> Void,
+  b: @escaping @Sendable () -> Void) {
+}
 
 func onClosure() {
+  // CHECK-LABEL: @__swiftmacro_10start_task0021start_taskswift_IfFDefMX35_16_33_EEC79532ED9A2723128F952F754D3F84Ll9StartTaskfMb_.swift
+  // CHECK: {
+  // CHECK:     Task {
+  // CHECK:         await f()
+  // CHECK:     }
+  // CHECK: }
   takeClosure { @StartTask in
     await f()
   }
+
+  // CHECK-LABEL: @__swiftmacro_10start_task0021start_taskswift_IfFDefMX45_16_33_EEC79532ED9A2723128F952F754D3F84Ll9StartTaskfMb_.swift
+  // CHECK: {
+  // CHECK:     Task {
+  // CHECK:         await f()
+  // CHECK:     }
+  // CHECK: }
+  takeClosure({ @StartTask in
+    await f()
+  }, v: 0)
+
+  // CHECK-LABEL: @__swiftmacro_10start_task0021start_taskswift_IfFDefMX55_21_33_EEC79532ED9A2723128F952F754D3F84Ll9StartTaskfMb_.swift
+  // CHECK: {
+  // CHECK:     Task {
+  // CHECK:         await f()
+  // CHECK:     }
+  // CHECK: }
+  multipleClosures { @StartTask in
+    await f()
+  } b: {
+  }
+
+  // CHECK-LABEL: @__swiftmacro_10start_task0021start_taskswift_IfFDefMX68_9_33_EEC79532ED9A2723128F952F754D3F84Ll9StartTaskfMb_.swift
+  // CHECK: {
+  // CHECK:     Task {
+  // CHECK:         await f()
+  // CHECK:     }
+  // CHECK: }
+  multipleClosures {
+    _ = 42
+  } b: { @StartTask in
+    await f()
+  }
+
+  // CHECK-LABEL: @__swiftmacro_10start_task0021start_taskswift_IfFDefMX86_4_33_EEC79532ED9A2723128F952F754D3F84Ll9StartTaskfMb_.swift
+  // CHECK: {
+  // CHECK:     Task {
+  // CHECK:         _ = 42
+  // CHECK:     }
+  // CHECK: }
+  
+  // CHECK-LABEL: @__swiftmacro_10start_task0021start_taskswift_IfFDefMX88_9_33_EEC79532ED9A2723128F952F754D3F84Ll9StartTaskfMb_.swift
+  // CHECK: {
+  // CHECK:     Task {
+  // CHECK:         await f()
+  // CHECK:     }
+  // CHECK: }
+  multipleClosures {
+    @StartTask in
+    _ = 42
+  } b: { @StartTask in
+    await f()
+  }
+
+  // CHECK-LABEL: @__swiftmacro_10start_task0021start_taskswift_IfFDefMX100_12_33_EEC79532ED9A2723128F952F754D3F84Ll9StartTaskfMb_.swift
+  // CHECK: {
+  // CHECK:     Task {
+  // CHECK:         await f()
+  // CHECK:     }
+  // CHECK: }
+  let _ = {
+    func test() {
+      _ = { @StartTask in await f() }
+    }
+  }
+
+  // CHECK-LABEL: @__swiftmacro_10start_task0021start_taskswift_IfFDefMX114_54_33_EEC79532ED9A2723128F952F754D3F84Ll9StartTaskfMb_.swift
+  // CHECK: {
+  // CHECK:     Task {
+  // CHECK:         await test()
+  // CHECK:     }
+  // CHECK: }
+  let _ = {
+    let y = 42
+    func test() async { print(y) }
+    
+    if case let (_, closure) = (otherValue: 42, fn: { @StartTask in
+         await test()
+      }) {
+      let _: Task<(), Never> = closure()
+    }
+  }
 }