From 50d52e1f51a160bff010ed073676f6e4f6870bae Mon Sep 17 00:00:00 2001
From: Nate Cook <natecook@apple.com>
Date: Sat, 14 May 2022 21:28:38 -0500
Subject: [PATCH] Remove the last SPI use of _RegexParser symbols

PatternConverter uses one last AST-based API defined in
_StringProcessing, which is technically not allowed but not
problematic b/c PatternConverter also imports _RegexParser.
However, this can have compile-time problems later on, so
this changes the entry point for PatternConverter to just use
an Any parameter that is checked at runtime to actually be AST.
---
 .../PatternConverter/PatternConverter.swift   |  3 +-
 .../_StringProcessing/PrintAsPattern.swift    | 32 +++++++++++--------
 2 files changed, 21 insertions(+), 14 deletions(-)

diff --git a/Sources/PatternConverter/PatternConverter.swift b/Sources/PatternConverter/PatternConverter.swift
index 497d54506..57e2f31dd 100644
--- a/Sources/PatternConverter/PatternConverter.swift
+++ b/Sources/PatternConverter/PatternConverter.swift
@@ -70,7 +70,8 @@ struct PatternConverter: ParsableCommand {
 
     print()
     if !skipDSL {
-      let render = ast.renderAsBuilderDSL(
+      let render = renderAsBuilderDSL(
+        ast: ast,
         maxTopDownLevels: topDownConversionLimit,
         minBottomUpLevels: bottomUpConversionLimit
       )
diff --git a/Sources/_StringProcessing/PrintAsPattern.swift b/Sources/_StringProcessing/PrintAsPattern.swift
index 0561c8c9b..3058a3956 100644
--- a/Sources/_StringProcessing/PrintAsPattern.swift
+++ b/Sources/_StringProcessing/PrintAsPattern.swift
@@ -17,20 +17,26 @@
 //       incremental conversion, such that leaves remain
 //       as canonical regex literals.
 
+/// Renders an AST tree as a Pattern DSL.
+///
+/// - Parameters:
+///   - ast: A `_RegexParser.AST` instance.
+///   - maxTopDownLevels: The number of levels down from the root of the tree
+///     to perform conversion. `nil` means no limit.
+///   - minBottomUpLevels: The number of levels up from the leaves of the tree
+///     to perform conversion. `nil` means no limit.
+/// - Returns: A string representation of `ast` in the `RegexBuilder` syntax.
 @_spi(PatternConverter)
-extension AST {
-  /// Renders as a Pattern DSL.
-  @_spi(PatternConverter)
-  public func renderAsBuilderDSL(
-    maxTopDownLevels: Int? = nil,
-    minBottomUpLevels: Int? = nil
-  ) -> String {
-    var printer = PrettyPrinter(
-      maxTopDownLevels: maxTopDownLevels,
-      minBottomUpLevels: minBottomUpLevels)
-    printer.printAsPattern(self)
-    return printer.finish()
-  }
+public func renderAsBuilderDSL(
+  ast: Any,
+  maxTopDownLevels: Int? = nil,
+  minBottomUpLevels: Int? = nil
+) -> String {
+  var printer = PrettyPrinter(
+    maxTopDownLevels: maxTopDownLevels,
+    minBottomUpLevels: minBottomUpLevels)
+  printer.printAsPattern(ast as! AST)
+  return printer.finish()
 }
 
 extension PrettyPrinter {