Add support for simple object-like macros (#6326)

Adds support for object-like macros with a single replacement
numeric-literal kind token. Only macros that evaluate to an integer
constant are supported for now. When detected at name lookup, they are
imported as a constant integer value in Carbon.

Demo:

```c++
// --- macros.h

#define CONFIG_VALUE 2
```

``` c++
// main.carbon
library "Main";

import Cpp library "macros.h";
import Core library "io";

fn Run() {
    let a: i32 = Cpp.CONFIG_VALUE;
    Core.Print(a);
}
```

```c++
$ bazel-bin/toolchain/carbon compile main.carbon
$ bazel-bin/toolchain/carbon link main.o \--output=demo_carbon
$ ./demo_carbon
2
```

Part of #6303

toolchain/check/BUILD

@@ -26,6 +26,7 @@ cc_library(
         "cpp/custom_type_mapping.cpp",
         "cpp/import.cpp",
         "cpp/location.cpp",
+        "cpp/macros.cpp",
         "cpp/operators.cpp",
         "cpp/overload_resolution.cpp",
         "cpp/thunk.cpp",
@@ -78,6 +79,7 @@ cc_library(
         "cpp/custom_type_mapping.h",
         "cpp/import.h",
         "cpp/location.h",
+        "cpp/macros.h",
         "cpp/operators.h",
         "cpp/overload_resolution.h",
         "cpp/thunk.h",

toolchain/check/cpp/import.cpp

@@ -27,6 +27,7 @@
 #include "common/ostream.h"
 #include "common/raw_string_ostream.h"
 #include "llvm/ADT/IntrusiveRefCntPtr.h"
+#include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/raw_ostream.h"
 #include "toolchain/base/kind_switch.h"
@@ -37,6 +38,7 @@
 #include "toolchain/check/convert.h"
 #include "toolchain/check/cpp/access.h"
 #include "toolchain/check/cpp/custom_type_mapping.h"
+#include "toolchain/check/cpp/macros.h"
 #include "toolchain/check/cpp/thunk.h"
 #include "toolchain/check/diagnostic_helpers.h"
 #include "toolchain/check/eval.h"
@@ -2252,6 +2254,86 @@ static auto IsIncompleteClass(Context& context, SemIR::NameScopeId scope_id)
              context.classes().Get(class_decl->class_id).self_type_id);
 }
 
+// Maps a Clang constant expression to a Carbon constant. Currently supports
+// only integer constants.
+// TODO: Add support for the other constant types for which a C++ to Carbon type
+// mapping exists.
+static auto MapConstant(Context& context, SemIR::LocId loc_id,
+                        clang::Expr* expr) -> SemIR::InstId {
+  CARBON_CHECK(expr, "empty expression");
+  auto* integer_literal = dyn_cast<clang::IntegerLiteral>(expr);
+  if (!integer_literal) {
+    context.TODO(
+        loc_id, "Unsupported: constant type: " + expr->getType().getAsString());
+    return SemIR::ErrorInst::InstId;
+  }
+  SemIR::TypeId type_id =
+      MapType(context, loc_id, integer_literal->getType()).type_id;
+  if (!type_id.has_value()) {
+    CARBON_DIAGNOSTIC(InCppConstantMapping, Error, "invalid integer type");
+    context.emitter().Emit(loc_id, InCppConstantMapping);
+    return SemIR::ErrorInst::InstId;
+  }
+  auto int_id = context.ints().Add(integer_literal->getValue().getSExtValue());
+  auto inst_id = AddInstInNoBlock<SemIR::IntValue>(
+      context, loc_id, {.type_id = type_id, .int_id = int_id});
+  context.imports().push_back(inst_id);
+  return inst_id;
+}
+
+// Imports a macro definition into the scope. Currently supports only simple
+// object-like macros that expand to a constant integer value.
+// TODO: Add support for other macro types and non-integer literal values.
+static auto ImportMacro(Context& context, SemIR::LocId loc_id,
+                        SemIR::NameScopeId scope_id, SemIR::NameId name_id,
+                        clang::MacroInfo* macro_info)
+    -> SemIR::ScopeLookupResult {
+  clang::Expr* macro_expr =
+      TryEvaluateMacroToConstant(context, loc_id, name_id, macro_info);
+
+  if (!macro_expr) {
+    return SemIR::ScopeLookupResult::MakeNotFound();
+  }
+
+  auto inst_id = MapConstant(context, loc_id, macro_expr);
+  if (inst_id == SemIR::ErrorInst::InstId) {
+    return SemIR::ScopeLookupResult::MakeNotFound();
+  }
+
+  AddNameToScope(context, scope_id, name_id, SemIR::AccessKind::Public,
+                 inst_id);
+  return SemIR::ScopeLookupResult::MakeWrappedLookupResult(
+      inst_id, SemIR::AccessKind::Public);
+}
+
+// Looks up a macro definition in the top-level `Cpp` scope. Returns nullptr if
+// the macro is not found or the scope is not the top-level `Cpp` scope.
+static auto LookupMacro(Context& context, SemIR::NameScopeId scope_id,
+                        SemIR::NameId name_id) -> clang::MacroInfo* {
+  auto name_str_opt = context.names().GetAsStringIfIdentifier(name_id);
+  if (!name_str_opt || !IsTopCppScope(context, scope_id)) {
+    return nullptr;
+  }
+
+  clang::Preprocessor& preprocessor = context.clang_sema().getPreprocessor();
+  // TODO: Do the identifier lookup only once, rather than both here and in
+  // ClangLookupName.
+  clang::IdentifierInfo* identifier_info =
+      preprocessor.getIdentifierInfo(*name_str_opt);
+
+  if (!identifier_info) {
+    return nullptr;
+  }
+
+  clang::MacroInfo* macro_info = preprocessor.getMacroInfo(identifier_info);
+  if (macro_info && !macro_info->isUsedForHeaderGuard() &&
+      !macro_info->isFunctionLike() && !macro_info->isBuiltinMacro()) {
+    return macro_info;
+  }
+
+  return nullptr;
+}
+
 auto ImportNameFromCpp(Context& context, SemIR::LocId loc_id,
                        SemIR::NameScopeId scope_id, SemIR::NameId name_id)
     -> SemIR::ScopeLookupResult {
@@ -2264,6 +2346,9 @@ auto ImportNameFromCpp(Context& context, SemIR::LocId loc_id,
   if (IsIncompleteClass(context, scope_id)) {
     return SemIR::ScopeLookupResult::MakeError();
   }
+  if (clang::MacroInfo* macro_info = LookupMacro(context, scope_id, name_id)) {
+    return ImportMacro(context, loc_id, scope_id, name_id, macro_info);
+  }
   auto lookup = ClangLookupName(context, scope_id, name_id);
   if (!lookup) {
     return ImportBuiltinTypesIntoScope(context, loc_id, scope_id, name_id);
@@ -2280,6 +2365,7 @@ auto ImportNameFromCpp(Context& context, SemIR::LocId loc_id,
                                       lookup->getNamingClass(),
                                       std::move(overload_set));
   }
+
   if (!lookup->isSingleResult()) {
     // Clang will diagnose ambiguous lookup results for us.
     if (!lookup->isAmbiguous()) {

toolchain/check/cpp/macros.cpp

@@ -0,0 +1,46 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include "toolchain/check/cpp/macros.h"
+
+#include "clang/AST/ASTContext.h"
+#include "clang/Sema/Sema.h"
+
+namespace Carbon::Check {
+
+auto TryEvaluateMacroToConstant(Context& context, SemIR::LocId loc_id,
+                                SemIR::NameId name_id,
+                                clang::MacroInfo* macro_info) -> clang::Expr* {
+  auto name_str_opt = context.names().GetAsStringIfIdentifier(name_id);
+  CARBON_CHECK(macro_info, "macro info missing");
+  if (macro_info->getNumTokens() != 1) {
+    context.TODO(loc_id,
+                 llvm::formatv("Unsupported: macro with {0} replacement tokens",
+                               macro_info->getNumTokens()));
+    return nullptr;
+  }
+  const clang::Token& tok = macro_info->getReplacementToken(0);
+  if (!tok.is(clang::tok::numeric_constant)) {
+    context.TODO(loc_id,
+                 "Unsupported: macro replacement token kind: " +
+                     std::string(clang::tok::getTokenName(tok.getKind())));
+    return nullptr;
+  }
+  clang::Sema& sema = context.clang_sema();
+  clang::ExprResult result = sema.ActOnNumericConstant(tok);
+  clang::Expr* result_expr = result.get();
+
+  if (!result_expr || result.isInvalid()) {
+    CARBON_DIAGNOSTIC(
+        InCppMacroEvaluation, Error,
+        "failed to evaluate macro Cpp.{0} to a valid constant expression",
+        std::string);
+    context.emitter().Emit(loc_id, InCppMacroEvaluation, (*name_str_opt).str());
+    return nullptr;
+  }
+
+  return result_expr;
+}
+
+}  // namespace Carbon::Check

toolchain/check/cpp/macros.h

@@ -0,0 +1,23 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#ifndef CARBON_TOOLCHAIN_CHECK_CPP_MACROS_H_
+#define CARBON_TOOLCHAIN_CHECK_CPP_MACROS_H_
+
+#include "toolchain/check/context.h"
+
+namespace Carbon::Check {
+
+// Tries to evaluate the given macro to a constant expression. Returns the
+// evaluated expression on success or nullptr otherwise. Currently supports only
+// simple object-like macros with a single replacement token that is a numeric
+// literal token.
+// TODO: Add support for multiple tokens and other literal types.
+auto TryEvaluateMacroToConstant(Context& context, SemIR::LocId loc_id,
+                                SemIR::NameId name_id,
+                                clang::MacroInfo* macro_info) -> clang::Expr*;
+
+}  // namespace Carbon::Check
+
+#endif  // CARBON_TOOLCHAIN_CHECK_CPP_MACROS_H_

toolchain/check/testdata/interop/cpp/macros.carbon

@@ -0,0 +1,502 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/primitives.carbon
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/macros.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/macros.carbon
+
+// ============================================================================
+// object-like macros
+// ============================================================================
+
+// --- integer_literal_replacement_token.h
+#define CONFIG_VALUE 42
+#define CONFIG_VALUE_LONG 42l
+#define CONFIG_VALUE_UNSIGNED 42u
+#define CONFIG_VALUE_HEXA 0xFF
+#define CONFIG_VALUE_OCTAL 010
+#define CONFIG_VALUE_BINARY 0b101
+
+// --- import_integer_literal_replacement_token.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "integer_literal_replacement_token.h";
+
+fn F() {
+  //@dump-sem-ir-begin
+  let a: i32 = Cpp.CONFIG_VALUE;
+  let b: i64 = Cpp.CONFIG_VALUE_LONG;
+  let c: u32 = Cpp.CONFIG_VALUE_UNSIGNED;
+  let d: i32 = Cpp.CONFIG_VALUE_HEXA;
+  let e: i32 = Cpp.CONFIG_VALUE_OCTAL;
+  let f: i32 = Cpp.CONFIG_VALUE_BINARY;
+  //@dump-sem-ir-end
+}
+
+// --- bad_suffix.h
+#define CONFIG_VALUE 42f
+
+// --- fail_import_bad_suffix.carbon
+
+library "[[@TEST_NAME]]";
+
+// CHECK:STDERR: fail_import_bad_suffix.carbon:[[@LINE+4]]:10: in file included here [InCppInclude]
+// CHECK:STDERR: ./bad_suffix.h:1:24: error: invalid digit 'f' in decimal constant [CppInteropParseError]
+// CHECK:STDERR:     1 | #define CONFIG_VALUE 42f
+// CHECK:STDERR:       |                        ^
+import Cpp library "bad_suffix.h";
+
+fn F() {
+  // CHECK:STDERR: fail_import_bad_suffix.carbon:[[@LINE+15]]:3: note: in `Cpp` name lookup for `CONFIG_VALUE` [InCppNameLookup]
+  // CHECK:STDERR:   Cpp.CONFIG_VALUE;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  // CHECK:STDERR: fail_import_bad_suffix.carbon:[[@LINE+11]]:3: error: failed to evaluate macro Cpp.CONFIG_VALUE to a valid constant expression [InCppMacroEvaluation]
+  // CHECK:STDERR:   Cpp.CONFIG_VALUE;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR: fail_import_bad_suffix.carbon:[[@LINE+8]]:3: note: in `Cpp` name lookup for `CONFIG_VALUE` [InCppNameLookup]
+  // CHECK:STDERR:   Cpp.CONFIG_VALUE;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  // CHECK:STDERR: fail_import_bad_suffix.carbon:[[@LINE+4]]:3: error: member name `CONFIG_VALUE` not found in `Cpp` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR:   Cpp.CONFIG_VALUE;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  Cpp.CONFIG_VALUE;
+}
+
+// --- integer_literal_too_big.h
+#define CONFIG_VALUE 18446744073709551616
+
+// --- fail_import_integer_literal_too_big.carbon
+
+library "[[@TEST_NAME]]";
+
+// CHECK:STDERR: fail_import_integer_literal_too_big.carbon:[[@LINE+4]]:10: in file included here [InCppInclude]
+// CHECK:STDERR: ./integer_literal_too_big.h:1:22: error: integer literal is too large to be represented in any integer type [CppInteropParseError]
+// CHECK:STDERR:     1 | #define CONFIG_VALUE 18446744073709551616
+// CHECK:STDERR:       |                      ^
+import Cpp library "integer_literal_too_big.h";
+
+fn F() {
+  // CHECK:STDERR: fail_import_integer_literal_too_big.carbon:[[@LINE+15]]:3: note: in `Cpp` name lookup for `CONFIG_VALUE` [InCppNameLookup]
+  // CHECK:STDERR:   Cpp.CONFIG_VALUE;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  // CHECK:STDERR: fail_import_integer_literal_too_big.carbon:[[@LINE+11]]:3: error: invalid integer type [InCppConstantMapping]
+  // CHECK:STDERR:   Cpp.CONFIG_VALUE;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR: fail_import_integer_literal_too_big.carbon:[[@LINE+8]]:3: note: in `Cpp` name lookup for `CONFIG_VALUE` [InCppNameLookup]
+  // CHECK:STDERR:   Cpp.CONFIG_VALUE;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  // CHECK:STDERR: fail_import_integer_literal_too_big.carbon:[[@LINE+4]]:3: error: member name `CONFIG_VALUE` not found in `Cpp` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR:   Cpp.CONFIG_VALUE;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  Cpp.CONFIG_VALUE;
+}
+
+// --- fail_assign_to_object_like_macro.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "integer_literal_replacement_token.h";
+
+fn F() {
+  // CHECK:STDERR: fail_assign_to_object_like_macro.carbon:[[@LINE+4]]:3: error: expression is not assignable [AssignmentToNonAssignable]
+  // CHECK:STDERR:   Cpp.CONFIG_VALUE = 3;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  Cpp.CONFIG_VALUE = 3;
+}
+
+// --- macro_in_nested_scope.h
+
+namespace N {
+  #define CONFIG_VALUE 42
+}
+
+// --- fail_import_macro_in_nested_scope.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "macro_in_nested_scope.h";
+
+fn F() {
+  let a: i32 = Cpp.CONFIG_VALUE;
+
+  // CHECK:STDERR: fail_import_macro_in_nested_scope.carbon:[[@LINE+4]]:16: error: member name `CONFIG_VALUE` not found in `Cpp.N` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR:   let b: i32 = Cpp.N.CONFIG_VALUE;
+  // CHECK:STDERR:                ^~~~~~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  let b: i32 = Cpp.N.CONFIG_VALUE;
+}
+
+// --- macro_and_non_macro_same_name.h
+
+namespace X {
+  float n;
+}
+float n;
+#define n 1
+
+// --- import_macro_and_non_macro_same_name.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "macro_and_non_macro_same_name.h";
+
+fn F() {
+  // When the same macro name and non-macro name exist in the global C++ scope, the macro name is selected.
+  // Cpp.n is treated as an integer constant with value 1.
+  var a: array(f32, Cpp.n) = (1.0,);
+
+  let b: f32 = Cpp.X.n;
+}
+
+// --- no_replacement_token.h
+#define MACRO_NAME
+
+// --- fail_import_no_replacement_token.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "no_replacement_token.h";
+
+fn F() {
+  // TODO: Get rid of the second error.
+  // CHECK:STDERR: fail_import_no_replacement_token.carbon:[[@LINE+11]]:3: error: semantics TODO: `Unsupported: macro with 0 replacement tokens` [SemanticsTodo]
+  // CHECK:STDERR:   Cpp.MACRO_NAME;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~
+  // CHECK:STDERR: fail_import_no_replacement_token.carbon:[[@LINE+8]]:3: note: in `Cpp` name lookup for `MACRO_NAME` [InCppNameLookup]
+  // CHECK:STDERR:   Cpp.MACRO_NAME;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  // CHECK:STDERR: fail_import_no_replacement_token.carbon:[[@LINE+4]]:3: error: member name `MACRO_NAME` not found in `Cpp` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR:   Cpp.MACRO_NAME;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  Cpp.MACRO_NAME;
+}
+
+// --- multiple_replacement_tokens_object_like_macro.h
+#define CONFIG_VALUE 1+2
+
+// --- fail_todo_import_multiple_replacement_tokens_object_like_macro.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "multiple_replacement_tokens_object_like_macro.h";
+
+fn F() {
+  // TODO: Get rid of the second error.
+  // CHECK:STDERR: fail_todo_import_multiple_replacement_tokens_object_like_macro.carbon:[[@LINE+11]]:16: error: semantics TODO: `Unsupported: macro with 3 replacement tokens` [SemanticsTodo]
+  // CHECK:STDERR:   let a: i32 = Cpp.CONFIG_VALUE;
+  // CHECK:STDERR:                ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR: fail_todo_import_multiple_replacement_tokens_object_like_macro.carbon:[[@LINE+8]]:16: note: in `Cpp` name lookup for `CONFIG_VALUE` [InCppNameLookup]
+  // CHECK:STDERR:   let a: i32 = Cpp.CONFIG_VALUE;
+  // CHECK:STDERR:                ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  // CHECK:STDERR: fail_todo_import_multiple_replacement_tokens_object_like_macro.carbon:[[@LINE+4]]:16: error: member name `CONFIG_VALUE` not found in `Cpp` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR:   let a: i32 = Cpp.CONFIG_VALUE;
+  // CHECK:STDERR:                ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  let a: i32 = Cpp.CONFIG_VALUE;
+}
+
+// --- string_literal_object_like_macro.h
+#define CONFIG_VALUE "abc"
+
+// --- fail_todo_import_string_literal_object_like_macro.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "string_literal_object_like_macro.h";
+
+fn F() {
+  // TODO: Get rid of the second error.
+  // CHECK:STDERR: fail_todo_import_string_literal_object_like_macro.carbon:[[@LINE+11]]:3: error: semantics TODO: `Unsupported: macro replacement token kind: string_literal` [SemanticsTodo]
+  // CHECK:STDERR:   Cpp.CONFIG_VALUE;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR: fail_todo_import_string_literal_object_like_macro.carbon:[[@LINE+8]]:3: note: in `Cpp` name lookup for `CONFIG_VALUE` [InCppNameLookup]
+  // CHECK:STDERR:   Cpp.CONFIG_VALUE;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  // CHECK:STDERR: fail_todo_import_string_literal_object_like_macro.carbon:[[@LINE+4]]:3: error: member name `CONFIG_VALUE` not found in `Cpp` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR:   Cpp.CONFIG_VALUE;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  Cpp.CONFIG_VALUE;
+}
+
+// --- floating_point_literal_macro.h
+#define PI 3.14
+
+// --- fail_todo_floating_point_literal_macro.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "floating_point_literal_macro.h";
+
+fn F() {
+  // TODO: Get rid of the second error.
+  // CHECK:STDERR: fail_todo_floating_point_literal_macro.carbon:[[@LINE+11]]:16: error: semantics TODO: `Unsupported: constant type: double` [SemanticsTodo]
+  // CHECK:STDERR:   let a: f64 = Cpp.PI;
+  // CHECK:STDERR:                ^~~~~~
+  // CHECK:STDERR: fail_todo_floating_point_literal_macro.carbon:[[@LINE+8]]:16: note: in `Cpp` name lookup for `PI` [InCppNameLookup]
+  // CHECK:STDERR:   let a: f64 = Cpp.PI;
+  // CHECK:STDERR:                ^~~~~~
+  // CHECK:STDERR:
+  // CHECK:STDERR: fail_todo_floating_point_literal_macro.carbon:[[@LINE+4]]:16: error: member name `PI` not found in `Cpp` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR:   let a: f64 = Cpp.PI;
+  // CHECK:STDERR:                ^~~~~~
+  // CHECK:STDERR:
+  let a: f64 = Cpp.PI;
+}
+
+// --- macro_undefined.h
+
+#define CONFIG_VALUE 1
+#undef CONFIG_VALUE
+
+// --- fail_macro_undefined.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "macro_undefined.h";
+
+fn F() {
+ // CHECK:STDERR: fail_macro_undefined.carbon:[[@LINE+4]]:15: error: member name `CONFIG_VALUE` not found in `Cpp` [MemberNameNotFoundInInstScope]
+ // CHECK:STDERR:  let a: i32 = Cpp.CONFIG_VALUE;
+ // CHECK:STDERR:               ^~~~~~~~~~~~~~~~
+ // CHECK:STDERR:
+ let a: i32 = Cpp.CONFIG_VALUE;
+}
+
+// --- macro_redefined.h
+
+#define CONFIG_VALUE 1
+#undef CONFIG_VALUE
+
+#define CONFIG_VALUE 2
+
+// --- import_macro_redefined.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "macro_redefined.h";
+
+fn F() {
+ let a: i32 = Cpp.CONFIG_VALUE;
+}
+
+// --- macro_defined_twice.h
+
+#define CONFIG_VALUE 1
+#define CONFIG_VALUE 2
+
+// --- import_macro_defined_twice.carbon
+
+library "[[@TEST_NAME]]";
+
+// CHECK:STDERR: import_macro_defined_twice.carbon:[[@LINE+9]]:10: in file included here [InCppInclude]
+// CHECK:STDERR: ./macro_defined_twice.h:3:9: warning: 'CONFIG_VALUE' macro redefined [CppInteropParseWarning]
+// CHECK:STDERR:     3 | #define CONFIG_VALUE 2
+// CHECK:STDERR:       |         ^
+// CHECK:STDERR: import_macro_defined_twice.carbon:[[@LINE+5]]:10: in file included here [InCppInclude]
+// CHECK:STDERR: ./macro_defined_twice.h:2:9: note: previous definition is here [CppInteropParseNote]
+// CHECK:STDERR:     2 | #define CONFIG_VALUE 1
+// CHECK:STDERR:       |         ^
+// CHECK:STDERR:
+import Cpp library "macro_defined_twice.h";
+
+fn F() {
+ let a: i32 = Cpp.CONFIG_VALUE;
+}
+
+// ============================================================================
+// function-like macros
+// ============================================================================
+
+// --- function_like_macros.h
+
+#define MAX(a, b) ((a) > (b) ? (a) : (b))
+
+// --- fail_todo_import_function_like_macros.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "function_like_macros.h";
+
+fn F() {
+  // CHECK:STDERR: fail_todo_import_function_like_macros.carbon:[[@LINE+4]]:16: error: member name `MAX` not found in `Cpp` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR:   let a: i32 = Cpp.MAX(1,2);
+  // CHECK:STDERR:                ^~~~~~~
+  // CHECK:STDERR:
+  let a: i32 = Cpp.MAX(1,2);
+}
+
+// ============================================================================
+// predefined macros
+// ============================================================================
+
+// --- predefined_macros.h
+
+auto foo() -> void;
+
+// --- fail_todo_import_predefined_macros.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "predefined_macros.h";
+
+fn F() {
+  // CHECK:STDERR: fail_todo_import_predefined_macros.carbon:[[@LINE+4]]:23: error: member name `__LINE__` not found in `Cpp` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR:   let line_num: i32 = Cpp.__LINE__;
+  // CHECK:STDERR:                       ^~~~~~~~~~~~
+  // CHECK:STDERR:
+  let line_num: i32 = Cpp.__LINE__;
+}
+
+// ============================================================================
+// macros used as header guards
+// ============================================================================
+
+// --- header_guard_macros.h
+
+#ifndef HEADER_GUARD_MACRO_H_
+#define HEADER_GUARD_MACRO_H_
+
+void foo();
+
+#endif  // HEADER_GUARD_MACRO_H_
+
+// --- fail_import_header_guard_macros.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "header_guard_macros.h";
+
+fn F() {
+  // CHECK:STDERR: fail_import_header_guard_macros.carbon:[[@LINE+4]]:3: error: member name `HEADER_GUARD_MACRO_H_` not found in `Cpp` [MemberNameNotFoundInInstScope]
+  // CHECK:STDERR:   Cpp.HEADER_GUARD_MACRO_H_;
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~~~~~~~~
+  // CHECK:STDERR:
+  Cpp.HEADER_GUARD_MACRO_H_;
+}
+
+// CHECK:STDOUT: --- import_integer_literal_replacement_token.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %int_32: Core.IntLiteral = int_value 32 [concrete]
+// CHECK:STDOUT:   %i32: type = class_type @Int, @Int(%int_32) [concrete]
+// CHECK:STDOUT:   %pattern_type.7ce: type = pattern_type %i32 [concrete]
+// CHECK:STDOUT:   %int_42.c68: %i32 = int_value 42 [concrete]
+// CHECK:STDOUT:   %int_64: Core.IntLiteral = int_value 64 [concrete]
+// CHECK:STDOUT:   %i64: type = class_type @Int, @Int(%int_64) [concrete]
+// CHECK:STDOUT:   %pattern_type.95b: type = pattern_type %i64 [concrete]
+// CHECK:STDOUT:   %int_42.434: %i64 = int_value 42 [concrete]
+// CHECK:STDOUT:   %u32: type = class_type @UInt, @UInt(%int_32) [concrete]
+// CHECK:STDOUT:   %pattern_type.4a9: type = pattern_type %u32 [concrete]
+// CHECK:STDOUT:   %int_42.58b: %u32 = int_value 42 [concrete]
+// CHECK:STDOUT:   %int_255: %i32 = int_value 255 [concrete]
+// CHECK:STDOUT:   %int_8: %i32 = int_value 8 [concrete]
+// CHECK:STDOUT:   %int_5: %i32 = int_value 5 [concrete]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
+// CHECK:STDOUT:     .CONFIG_VALUE = %int_42.c68
+// CHECK:STDOUT:     .CONFIG_VALUE_LONG = %int_42.434
+// CHECK:STDOUT:     .CONFIG_VALUE_UNSIGNED = %int_42.58b
+// CHECK:STDOUT:     .CONFIG_VALUE_HEXA = %int_255
+// CHECK:STDOUT:     .CONFIG_VALUE_OCTAL = %int_8
+// CHECK:STDOUT:     .CONFIG_VALUE_BINARY = %int_5
+// CHECK:STDOUT:     import Cpp//...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %int_42.c68: %i32 = int_value 42 [concrete = constants.%int_42.c68]
+// CHECK:STDOUT:   %int_42.434: %i64 = int_value 42 [concrete = constants.%int_42.434]
+// CHECK:STDOUT:   %int_42.58b: %u32 = int_value 42 [concrete = constants.%int_42.58b]
+// CHECK:STDOUT:   %int_255: %i32 = int_value 255 [concrete = constants.%int_255]
+// CHECK:STDOUT:   %int_8: %i32 = int_value 8 [concrete = constants.%int_8]
+// CHECK:STDOUT:   %int_5: %i32 = int_value 5 [concrete = constants.%int_5]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @F() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   name_binding_decl {
+// CHECK:STDOUT:     %a.patt: %pattern_type.7ce = value_binding_pattern a [concrete]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Cpp.ref.loc8: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT:   %CONFIG_VALUE.ref: %i32 = name_ref CONFIG_VALUE, imports.%int_42.c68 [concrete = constants.%int_42.c68]
+// CHECK:STDOUT:   %.loc8: type = splice_block %i32.loc8 [concrete = constants.%i32] {
+// CHECK:STDOUT:     %int_32.loc8: Core.IntLiteral = int_value 32 [concrete = constants.%int_32]
+// CHECK:STDOUT:     %i32.loc8: type = class_type @Int, @Int(constants.%int_32) [concrete = constants.%i32]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %a: %i32 = value_binding a, %CONFIG_VALUE.ref
+// CHECK:STDOUT:   name_binding_decl {
+// CHECK:STDOUT:     %b.patt: %pattern_type.95b = value_binding_pattern b [concrete]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Cpp.ref.loc9: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT:   %CONFIG_VALUE_LONG.ref: %i64 = name_ref CONFIG_VALUE_LONG, imports.%int_42.434 [concrete = constants.%int_42.434]
+// CHECK:STDOUT:   %.loc9: type = splice_block %i64.loc9 [concrete = constants.%i64] {
+// CHECK:STDOUT:     %int_64.loc9: Core.IntLiteral = int_value 64 [concrete = constants.%int_64]
+// CHECK:STDOUT:     %i64.loc9: type = class_type @Int, @Int(constants.%int_64) [concrete = constants.%i64]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %b: %i64 = value_binding b, %CONFIG_VALUE_LONG.ref
+// CHECK:STDOUT:   name_binding_decl {
+// CHECK:STDOUT:     %c.patt: %pattern_type.4a9 = value_binding_pattern c [concrete]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Cpp.ref.loc10: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT:   %CONFIG_VALUE_UNSIGNED.ref: %u32 = name_ref CONFIG_VALUE_UNSIGNED, imports.%int_42.58b [concrete = constants.%int_42.58b]
+// CHECK:STDOUT:   %.loc10: type = splice_block %u32.loc10 [concrete = constants.%u32] {
+// CHECK:STDOUT:     %int_32.loc10: Core.IntLiteral = int_value 32 [concrete = constants.%int_32]
+// CHECK:STDOUT:     %u32.loc10: type = class_type @UInt, @UInt(constants.%int_32) [concrete = constants.%u32]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %c: %u32 = value_binding c, %CONFIG_VALUE_UNSIGNED.ref
+// CHECK:STDOUT:   name_binding_decl {
+// CHECK:STDOUT:     %d.patt: %pattern_type.7ce = value_binding_pattern d [concrete]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Cpp.ref.loc11: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT:   %CONFIG_VALUE_HEXA.ref: %i32 = name_ref CONFIG_VALUE_HEXA, imports.%int_255 [concrete = constants.%int_255]
+// CHECK:STDOUT:   %.loc11: type = splice_block %i32.loc11 [concrete = constants.%i32] {
+// CHECK:STDOUT:     %int_32.loc11: Core.IntLiteral = int_value 32 [concrete = constants.%int_32]
+// CHECK:STDOUT:     %i32.loc11: type = class_type @Int, @Int(constants.%int_32) [concrete = constants.%i32]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %d: %i32 = value_binding d, %CONFIG_VALUE_HEXA.ref
+// CHECK:STDOUT:   name_binding_decl {
+// CHECK:STDOUT:     %e.patt: %pattern_type.7ce = value_binding_pattern e [concrete]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Cpp.ref.loc12: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT:   %CONFIG_VALUE_OCTAL.ref: %i32 = name_ref CONFIG_VALUE_OCTAL, imports.%int_8 [concrete = constants.%int_8]
+// CHECK:STDOUT:   %.loc12: type = splice_block %i32.loc12 [concrete = constants.%i32] {
+// CHECK:STDOUT:     %int_32.loc12: Core.IntLiteral = int_value 32 [concrete = constants.%int_32]
+// CHECK:STDOUT:     %i32.loc12: type = class_type @Int, @Int(constants.%int_32) [concrete = constants.%i32]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %e: %i32 = value_binding e, %CONFIG_VALUE_OCTAL.ref
+// CHECK:STDOUT:   name_binding_decl {
+// CHECK:STDOUT:     %f.patt: %pattern_type.7ce = value_binding_pattern f [concrete]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Cpp.ref.loc13: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT:   %CONFIG_VALUE_BINARY.ref: %i32 = name_ref CONFIG_VALUE_BINARY, imports.%int_5 [concrete = constants.%int_5]
+// CHECK:STDOUT:   %.loc13: type = splice_block %i32.loc13 [concrete = constants.%i32] {
+// CHECK:STDOUT:     %int_32.loc13: Core.IntLiteral = int_value 32 [concrete = constants.%int_32]
+// CHECK:STDOUT:     %i32.loc13: type = class_type @Int, @Int(constants.%int_32) [concrete = constants.%i32]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %f: %i32 = value_binding f, %CONFIG_VALUE_BINARY.ref
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT: }
+// CHECK:STDOUT:

toolchain/diagnostics/diagnostic_kind.def

@@ -375,6 +375,8 @@ CARBON_DIAGNOSTIC_KIND(QualifiedDeclInIncompleteClassScope)
 CARBON_DIAGNOSTIC_KIND(QualifiedDeclInUndefinedInterfaceScope)
 
 // Name lookup.
+CARBON_DIAGNOSTIC_KIND(InCppConstantMapping)
+CARBON_DIAGNOSTIC_KIND(InCppMacroEvaluation)
 CARBON_DIAGNOSTIC_KIND(InCppNameLookup)
 CARBON_DIAGNOSTIC_KIND(InNameLookup)
 CARBON_DIAGNOSTIC_KIND(IncompleteOperandTypeInCppOperatorLookup)