Add a flag to dump the AST as JSON.

include/swift/AST/DiagnosticsFrontend.def

@@ -585,5 +585,8 @@ ERROR(experimental_not_supported_in_production,none,
       "experimental feature '%0' cannot be enabled in production compiler",
       (StringRef))
 
+ERROR(zlib_not_supported,none,
+      "this compiler was not built with zlib compression support enabled", ())
+
 #define UNDEFINE_DIAGNOSTIC_MACROS
 #include "DefineDiagnosticMacros.h"

include/swift/AST/SourceFile.h

@@ -672,6 +672,8 @@ class SourceFile final : public FileUnit {
   SWIFT_DEBUG_DUMP;
   void dump(raw_ostream &os, bool parseIfNeeded = false) const;
 
+  void dumpJSON(ASTContext &ctx, raw_ostream &os);
+
   /// Pretty-print the contents of this source file.
   ///
   /// \param Printer The AST printer used for printing the contents.

include/swift/Frontend/FrontendOptions.h

@@ -434,6 +434,15 @@ class FrontendOptions {
   /// -dump-scope-maps.
   SmallVector<std::pair<unsigned, unsigned>, 2> DumpScopeMapLocations;
 
+  enum class ASTFormat {
+    Default,  ///< S-expressions for debugging
+    JSON,     ///< Structured JSON for analysis
+    JSONZlib, ///< Like JSON, but zlib-compressed
+  };
+
+  /// The output format generated by the `-dump-ast` flag.
+  ASTFormat DumpASTFormat = ASTFormat::Default;
+
   /// Determines whether the static or shared resource folder is used.
   /// When set to `true`, the default resource folder will be set to
   /// '.../lib/swift', otherwise '.../lib/swift_static'.

include/swift/Option/Options.td

@@ -1332,6 +1332,10 @@ def emit_parse : Flag<["-"], "emit-parse">, Alias<dump_parse>,
 def dump_ast : Flag<["-"], "dump-ast">,
   HelpText<"Parse and type-check input file(s) and dump AST(s)">, ModeOpt,
   Flags<[FrontendOption, NoInteractiveOption, DoesNotAffectIncrementalBuild]>;
+def dump_ast_format : Separate<["-"], "dump-ast-format">,
+  HelpText<"Desired format for -dump-ast output ('default', 'json', or 'json-zlib')">,
+  MetaVarName<"<format>">,
+  Flags<[FrontendOption, NoInteractiveOption, DoesNotAffectIncrementalBuild]>;
 def emit_ast : Flag<["-"], "emit-ast">, Alias<dump_ast>,
   Flags<[FrontendOption, NoInteractiveOption, DoesNotAffectIncrementalBuild]>;
 def dump_scope_maps : Separate<["-"], "dump-scope-maps">,

lib/AST/CMakeLists.txt

@@ -64,6 +64,7 @@ add_swift_host_library(swiftAST STATIC
   ImportCache.cpp
   IndexSubset.cpp
   InlinableText.cpp
+  JSONASTDumper.cpp
   LayoutConstraint.cpp
   LifetimeDependence.cpp
   LocalArchetypeRequirementCollector.cpp