[Macros] Fix emission of thrown errors.

Errors that were thrown out of a macro implementation were being
emitted and then lost. The result of this is a SILGen assertion later
on, if there were no other errors in the code.

Make sure we properly emit these diagnostics through the source
manager, which required fixing an issue in the offset computation used
for diagnostics.

Author: DougGregor

lib/ASTGen/Sources/ASTGen/Macros.swift

@@ -199,11 +199,11 @@ func expandFreestandingMacro(
         print("not on a macro expansion node: \(token.recursiveDescription)")
         return -1
       }
+      macroName = parentExpansion.macro.text
       let decls = try declMacro.expansion(
         of: sourceManager.detach(parentExpansion, in: context),
         in: context
       )
-      macroName = parentExpansion.macro.text
       evaluatedSyntax = Syntax(CodeBlockItemListSyntax(
         decls.map { CodeBlockItemSyntax(item: .decl($0)) }))
 
@@ -213,11 +213,12 @@ func expandFreestandingMacro(
     }
   } catch {
     // Record the error
-    context.diagnose(
-      Diagnostic(
+    sourceManager.diagnose(
+      diagnostic: Diagnostic(
         node: parentSyntax,
         message: ThrownErrorDiagnostic(message: String(describing: error))
-      )
+      ),
+      messageSuffix: " (from macro '\(macroName)')"
     )
     return -1
   }
@@ -426,11 +427,12 @@ func expandAttachedMacro(
   } catch {
     // Record the error
     // FIXME: Need to decide where to diagnose the error:
-    context.diagnose(
-      Diagnostic(
+    sourceManager.diagnose(
+      diagnostic: Diagnostic(
         node: Syntax(declarationNode),
         message: ThrownErrorDiagnostic(message: String(describing: error))
-      )
+      ),
+      messageSuffix: " (from macro '\(macroName)')"
     )
 
     return 1

lib/ASTGen/Sources/ASTGen/SourceManager.swift

@@ -76,13 +76,17 @@ extension SourceManager {
       return nil
     }
 
-    // Recursively find the root and its offset. This also must succeed.
+    // Recursively find the root and its offset.
     guard let (rootSF, parentOffset) = rootSourceFile(of: parent) else {
       return nil
     }
 
-    // Add our offset to our parent's offset, and we're done.
-    return (rootSF, parentOffset + SourceLength(utf8Length: offset))
+    // The position of our node is...
+    let finalPosition =
+      node.position                      // Our position relative to its root
+      + SourceLength(utf8Length: offset) // and that root's offset in its parent
+      + SourceLength(utf8Length: parentOffset.utf8Offset)
+    return (rootSF, finalPosition)
   }
 
   /// Produce the C++ source location for a given position based on a
@@ -106,7 +110,7 @@ extension SourceManager {
     // node.
     let position = position ?? node.position
     let offsetWithinSyntaxNode =
-       position.utf8Offset - node.root.position.utf8Offset
+       position.utf8Offset - node.position.utf8Offset
     let offsetFromSourceFile = rootPosition.utf8Offset + offsetWithinSyntaxNode
 
     // Compute the resulting address.

test/Macros/Inputs/syntax_macro_definitions.swift

@@ -147,15 +147,6 @@ public enum AddBlocker: ExpressionMacro {
     of node: some FreestandingMacroExpansionSyntax,
     in context: some MacroExpansionContext
   ) -> ExprSyntax {
-    let opTable = OperatorTable.standardOperators
-    let node = opTable.foldAll(node) { error in
-      context.diagnose(error.asDiagnostic)
-    }.asProtocol(FreestandingMacroExpansionSyntax.self)!
-
-    guard let argument = node.argumentList.first?.expression else {
-      fatalError("boom")
-    }
-
     let visitor = AddVisitor()
     let result = visitor.visit(Syntax(node))
 
@@ -242,6 +233,35 @@ public struct DefineBitwidthNumberedStructsMacro: DeclarationMacro {
   }
 }
 
+public struct WarningMacro: ExpressionMacro {
+   public static func expansion(
+     of macro: some FreestandingMacroExpansionSyntax,
+     in context: some MacroExpansionContext
+   ) throws -> ExprSyntax {
+     guard let firstElement = macro.argumentList.first,
+       let stringLiteral = firstElement.expression
+         .as(StringLiteralExprSyntax.self),
+       stringLiteral.segments.count == 1,
+       case let .stringSegment(messageString)? = stringLiteral.segments.first
+     else {
+       throw CustomError.message("#myWarning macro requires a string literal")
+     }
+
+     context.diagnose(
+       Diagnostic(
+         node: Syntax(macro),
+         message: SimpleDiagnosticMessage(
+           message: messageString.content.description,
+           diagnosticID: MessageID(domain: "test", id: "error"),
+           severity: .warning
+         )
+       )
+     )
+
+     return "()"
+  }
+}
+
 public struct PropertyWrapperMacro {}
 
 extension PropertyWrapperMacro: AccessorMacro, Macro {

test/Macros/macro_expand.swift

@@ -11,6 +11,8 @@
 // Debug info SIL testing
 // RUN: %target-swift-frontend -emit-sil -enable-experimental-feature Macros -enable-experimental-feature Macros -load-plugin-library %t/%target-library-name(MacroDefinition) -I %swift-host-lib-dir %s -module-name MacroUser -o - -g | %FileCheck --check-prefix CHECK-SIL %s
 
+// RUN: %target-swift-frontend -emit-sil -enable-experimental-feature Macros -enable-experimental-feature Macros -load-plugin-library %t/%target-library-name(MacroDefinition) -I %swift-host-lib-dir %s -module-name MacroUser -o - -g | %FileCheck --check-prefix CHECK-SIL %s
+
 // Execution testing
 // RUN: %target-build-swift -g -enable-experimental-feature Macros -enable-experimental-feature Macros -load-plugin-library %t/%target-library-name(MacroDefinition) -I %swift-host-lib-dir -L %swift-host-lib-dir %s -o %t/main -module-name MacroUser
 // RUN: %target-run %t/main | %FileCheck %s

test/Macros/macro_expand_throwing.swift

@@ -0,0 +1,17 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift -I %swift-host-lib-dir -L %swift-host-lib-dir -emit-library -o %t/%target-library-name(MacroDefinition) -module-name=MacroDefinition %S/Inputs/syntax_macro_definitions.swift -g -no-toolchain-stdlib-rpath -swift-version 5
+
+// Make sure the diagnostic comes through...
+// RUN: %target-typecheck-verify-swift -enable-experimental-feature Macros -load-plugin-library %t/%target-library-name(MacroDefinition) -I %swift-host-lib-dir -module-name MacroUser
+
+// Make sure the diagnostic doesn't crash in SILGen
+// RUN: not %target-swift-frontend -emit-sil -enable-experimental-feature Macros -enable-experimental-feature Macros -load-plugin-library %t/%target-library-name(MacroDefinition) -I %swift-host-lib-dir %s -module-name MacroUser -o - -g
+
+@freestanding(expression) macro myWarning(_ message: String) = #externalMacro(module: "MacroDefinition", type: "WarningMacro")
+
+func testThrownError() {
+  let name = "hello"
+  #myWarning(name) // expected-error{{#myWarning macro requires a string literal (from macro 'myWarning')}}
+
+  #myWarning("experimental features ahead") // expected-warning{{experimental features ahead}}
+}