[Macros] Unpack DiagnosticsError into separate diagnostics

Fixes rdar://107289985.

Author: DougGregor

lib/ASTGen/Sources/ASTGen/Macros.swift

@@ -373,6 +373,14 @@ func expandFreestandingMacroInProcess(
       print("not an expression macro or a declaration macro")
       return nil
     }
+  } catch let diagsError as DiagnosticsError {
+    for diag in diagsError.diagnostics {
+      sourceManager.diagnose(
+        diagnostic: diag,
+        messageSuffix: " (from macro '\(macroName)')"
+      )
+    }
+    return nil
   } catch {
     // Record the error
     sourceManager.diagnose(
@@ -805,6 +813,15 @@ func expandAttachedMacroInProcess(
       print("\(macroPtr) does not conform to any known attached macro protocol")
       return nil
     }
+  } catch let diagsError as DiagnosticsError {
+    for diag in diagsError.diagnostics {
+      sourceManager.diagnose(
+        diagnostic: diag,
+        messageSuffix: " (from macro '\(macroName)')"
+      )
+    }
+
+    return nil
   } catch {
     // Record the error
     // FIXME: Need to decide where to diagnose the error:

test/Macros/Inputs/syntax_macro_definitions.swift

@@ -316,6 +316,51 @@ public struct WarningMacro: ExpressionMacro {
   }
 }
 
+public struct ErrorMacro: 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 {
+        let errorNode: Syntax
+          if let firstElement = macro.argumentList.first {
+          errorNode = Syntax(firstElement)
+        } else {
+          errorNode = Syntax(macro)
+        }
+
+        let messageID = MessageID(domain: "silly", id: "error")
+        let diag = Diagnostic(
+          node: errorNode,
+          message: SimpleDiagnosticMessage(
+            message: "#myError macro requires a string literal",
+            diagnosticID: messageID,
+            severity: .error
+          )
+        )
+
+       throw DiagnosticsError(diagnostics: [diag])
+     }
+
+     context.diagnose(
+       Diagnostic(
+         node: Syntax(macro),
+         message: SimpleDiagnosticMessage(
+           message: messageString.content.description,
+           diagnosticID: MessageID(domain: "test", id: "error"),
+           severity: .error
+         )
+       )
+     )
+
+     return "()"
+  }
+}
+
 public struct PropertyWrapperMacro {}
 
 extension PropertyWrapperMacro: AccessorMacro, Macro {

test/Macros/macro_expand_throwing.swift

@@ -2,7 +2,7 @@
 // RUN: %target-build-swift -swift-version 5 -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 -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) -I %swift-host-lib-dir -module-name MacroUser
+// RUN: %target-typecheck-verify-swift -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) -I %swift-host-lib-dir -module-name MacroUser -DTEST_DIAGNOSTICS
 
 // Make sure the diagnostic doesn't crash in SILGen
 // RUN: not %target-swift-frontend -swift-version 5 -emit-sil -load-plugin-library %t/%target-library-name(MacroDefinition) -I %swift-host-lib-dir %s -module-name MacroUser -o - -g
@@ -12,9 +12,22 @@
 
 @freestanding(expression) macro myWarning(_ message: String) = #externalMacro(module: "MacroDefinition", type: "WarningMacro")
 
+@freestanding(expression) macro myError(_ message: String) = #externalMacro(module: "MacroDefinition", type: "ErrorMacro")
+
 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}}
 }
+
+#if TEST_DIAGNOSTICS
+func testThrownErrors() {
+  let name = "hello"
+  #myError(
+    name
+  ) // expected-error@-1{{macro requires a string literal (from macro 'myError')}}
+
+  #myError("experimental features ahead") // expected-error{{experimental features ahead}}
+}
+#endif