[macros] add -Rmacro-expansions

This adds the -Rmacro-expansions flag. It provides similar functionality
to -dump-macro-expansions, but instead of dumping the macro expansion to
stderr, it emits it line by line as remarks. This is useful for testing
with -verify, where both macro expansion content and warnings need to be
tested at the same time.

include/swift/AST/DiagnosticsSema.def

@@ -9012,5 +9012,7 @@ GROUPED_WARNING(perf_hint_typealias_uses_existential,ExistentialType,none,
 ERROR(unsafe_self_dependent_result_attr_on_invalid_decl,none,
       "invalid use of @_unsafeSelfDependentResult", ())
 
+REMARK(macro_expansion_line, none, "macro content: |%0|", (StringRef))
+
 #define UNDEFINE_DIAGNOSTIC_MACROS
 #include "DefineDiagnosticMacros.h"

include/swift/Basic/LangOptions.h

@@ -651,6 +651,9 @@ namespace swift {
     /// Enables dumping macro expansions.
     bool DumpMacroExpansions = false;
 
+    /// Emits a remark with the content of each macro expansion line, for matching with -verify
+    bool RemarkMacroExpansions = false;
+
     /// Enables dumping imports for each SourceFile.
     bool DumpSourceFileImports = false;
 

include/swift/Option/FrontendOptions.td

@@ -185,6 +185,9 @@ def verify_generic_signatures : Separate<["-"], "verify-generic-signatures">,
   MetaVarName<"<module-name>">,
   HelpText<"Verify the generic signatures in the given module">;
 
+def expansion_remarks:  Flag<["-"], "Rmacro-expansions">,
+  HelpText<"Show remarks for each line in macro expansions">;
+
 def show_diagnostics_after_fatal : Flag<["-"], "show-diagnostics-after-fatal">,
   HelpText<"Keep emitting subsequent diagnostics after a fatal error">;
 

lib/Frontend/CompilerInvocation.cpp

@@ -1774,6 +1774,9 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   Opts.DumpMacroExpansions = Args.hasArg(
       OPT_dump_macro_expansions);
 
+  Opts.RemarkMacroExpansions = Args.hasArg(
+      OPT_expansion_remarks);
+
   Opts.DumpSourceFileImports = Args.hasArg(
       OPT_dump_source_file_imports);
 

lib/Sema/TypeCheckMacros.cpp

@@ -1006,6 +1006,21 @@ static CharSourceRange getExpansionInsertionRange(MacroRole role,
   llvm_unreachable("unhandled MacroRole");
 }
 
+static void remarkMacroExpansionsEmitDiags(ASTContext &ctx, unsigned macroBufferID) {
+  SourceManager &sourceMgr = ctx.SourceMgr;
+  CharSourceRange range = sourceMgr.getRangeForBuffer(macroBufferID);
+  SourceLoc start = range.getStart();
+  StringRef content(start.getPointer(), range.getByteLength());
+  size_t newline;
+  do {
+    newline = content.find('\n');
+    StringRef line = content.take_front(newline);
+    content = content.drop_front(newline + 1);
+
+    ctx.Diags.diagnose(SourceLoc::getFromPointer(line.begin()), diag::macro_expansion_line, line);
+  } while (newline != StringRef::npos);
+}
+
 static SourceFile *
 createMacroSourceFile(std::unique_ptr<llvm::MemoryBuffer> buffer,
                       MacroRole role, ASTNode target, DeclContext *dc,
@@ -1069,6 +1084,10 @@ createMacroSourceFile(std::unique_ptr<llvm::MemoryBuffer> buffer,
       originModule = cast<Decl *>(target)->getModuleContextForNameLookup();
     performImportResolutionForClangMacroBuffer(*macroSourceFile, originModule);
   }
+
+  if (ctx.LangOpts.RemarkMacroExpansions)
+    remarkMacroExpansionsEmitDiags(ctx, macroBufferID);
+
   return macroSourceFile;
 }
 

test/Frontend/DiagnosticVerifier/Inputs/macro/unstringify-macro.swift

@@ -0,0 +1,19 @@
+import SwiftSyntax
+import SwiftSyntaxBuilder
+import SwiftSyntaxMacros
+
+public struct UnstringifyPeerMacro: PeerMacro {
+  public static func expansion(
+    of node: AttributeSyntax,
+    providingPeersOf declaration: some DeclSyntaxProtocol,
+    in context: some MacroExpansionContext
+  ) throws -> [DeclSyntax] {
+    do {
+      let argumentList = node.arguments!.as(LabeledExprListSyntax.self)!
+      let arguments = [LabeledExprSyntax](argumentList)
+      let arg = arguments.first!.expression.as(StringLiteralExprSyntax.self)!
+      let content = arg.representedLiteralValue!
+      return [DeclSyntax("\(raw: content)")]
+    }
+  }
+}

test/Frontend/DiagnosticVerifier/expansion-remarks.swift

@@ -0,0 +1,36 @@
+// REQUIRES: swift_swift_parser, executable_test
+
+// RUN: %empty-directory(%t)
+// RUN: %host-build-swift -swift-version 5 -emit-library -o %t/%target-library-name(UnstringifyMacroDefinition) -module-name=UnstringifyMacroDefinition %S/Inputs/macro/unstringify-macro.swift -g -no-toolchain-stdlib-rpath
+
+// RUN: %target-typecheck-verify-swift -swift-version 5 -load-plugin-library %t/%target-library-name(UnstringifyMacroDefinition) -Rmacro-expansions
+
+@attached(peer, names: overloaded)
+macro unstringifyPeer(_ s: String) =
+    #externalMacro(module: "UnstringifyMacroDefinition", type: "UnstringifyPeerMacro")
+
+// expected-note@+1 *{{in expansion of macro 'unstringifyPeer' on global function 'foo()' here}}
+@unstringifyPeer("func foo(_ x: Int) {\nlet a = 2\nlet b = x\n}")
+func foo() {}
+/*
+expected-expansion@-2:14{{
+    expected-remark@1{{macro content: |func foo(_ x: Int) {|}}
+    expected-remark@2{{macro content: |    let a = 2|}}
+    expected-warning@2{{initialization of immutable value 'a' was never used; consider replacing with assignment to '_' or removing it}}
+    expected-remark@3{{macro content: |    let b = x|}}
+    expected-warning@3{{initialization of immutable value 'b' was never used; consider replacing with assignment to '_' or removing it}}
+    expected-remark@4{{macro content: |}|}}
+}}
+*/
+
+@freestanding(expression) public macro ExprMacro() -> String = #file
+
+func bar() {
+    // expected-note@+1{{in expansion of macro 'ExprMacro' here}}
+    let _ = #ExprMacro()
+    /*
+    expected-expansion@-2:13{{
+        expected-remark@1{{macro content: |#file|}}
+    }}
+    */
+}