Support headers using symbols mapped to themselves

Currently if IWYU decides that the best header for a symbol is the same
one that uses the symbol, it can cause that header to add a #include of
itself.

This in particular can happen with mappings.

Detect this case and cause the use to be ignored.

Furthermore, when choosing from multiple public mapping headers, prefer
to use oneself where possible (since that minimizes #includes).

iwyu_output.cc

@@ -763,6 +763,7 @@ bool DeclIsVisibleToUseInSameFile(const Decl* decl, const OneUse& use) {
 // files.  For everything but foo.cc, this is empty; for foo.cc it's
 // foo.h's includes and foo-inl.h's includes.
 set<string> CalculateMinimalIncludes(
+    const string& use_quoted_include,
     const set<string>& direct_includes,
     const set<string>& associated_direct_includes,
     vector<OneUse>* uses) {
@@ -803,18 +804,29 @@ set<string> CalculateMinimalIncludes(
   }
 
   // Steps (2): Go through the needed private-includes that map to
-  // more than one public #include.  First choice: an include in
-  // associated_direct_includes (those are includes that are not going
-  // away, since we can't change associated files).  Second choice,
-  // includes in direct_includes that are also already in
-  // desired_headers.  Third choice, includes in desired_headers.
-  // Fourth choice, includes in direct_includes.  Picking in
-  // this order minimizes the number of #includes we add, while
-  // allowing us to remove #includes if need be.
+  // more than one public #include.  Use the following priority order:
+  // - Ourselves.
+  // - An include in associated_direct_includes (those are includes
+  //   that are not going away, since we can't change associated
+  //   files).
+  // - Includes in direct_includes that are also already in
+  //   desired_headers.
+  // - Includes in desired_headers.
+  // - Includes in direct_includes.
+  // Picking in this order minimizes the number of #includes we add,
+  // while allowing us to remove #includes if need be.
   for (OneUse& use : *uses) {
     if (!use.NeedsSuggestedHeader())
       continue;
     const vector<string>& public_headers = use.public_headers();
+    for (const string& choice : public_headers) {
+      if (use.has_suggested_header())
+        break;
+      if (choice == use_quoted_include) {
+        use.set_suggested_header(choice);
+        LogIncludeMapping("in self", use);
+      }
+    }
     // TODO(csilvers): write ElementInBoth() in iwyu_stl_util.h
     for (const string& choice : public_headers) {
       if (use.has_suggested_header())
@@ -987,7 +999,9 @@ set<string> CalculateMinimalIncludes(
 // Calculate IWYU violations for full uses:
 // E1) Sanity check: ignore the use if it would require adding an
 //     #include of a .cc file.
-// E2) If the desired include-file for this symbols is not in the
+// E2) Ignore use when the suggested header *is* the current file
+//     (this can happen due to mappings).
+// E3) If the desired include-file for this symbols is not in the
 //     current includes, mark as an iwyu violation.
 
 void ProcessForwardDeclare(OneUse* use,
@@ -1427,7 +1441,8 @@ void CalculateIwyuForForwardDeclareUse(
 }
 
 void CalculateIwyuForFullUse(OneUse* use,
-                             const set<string>& actual_includes) {
+                             const set<string>& actual_includes,
+                             const string& use_quoted_include) {
   CHECK_(!use->ignore_use() && "Trying to calculate on an ignored use");
   CHECK_(use->is_full_use() && "CalculateIwyuForFullUse requires a full use");
   CHECK_(use->has_suggested_header() && "All full uses must have a header");
@@ -1472,7 +1487,18 @@ void CalculateIwyuForFullUse(OneUse* use,
     return;
   }
 
-  // (E2) Mark iwyu violation unless in a current #include.
+  // (E2) Ignore use when the suggested header *is* the current file (this can
+  // happen due to mappings).
+  if (use_quoted_include == use->suggested_header()) {
+    VERRS(6) << "Ignoring full use of " << use->symbol_name()
+             << " (" << use->PrintableUseLoc()
+             << "): use already in suggested header "
+             << use->suggested_header() << "\n";
+    use->set_ignore_use();
+    return;
+  }
+
+  // (E3) Mark iwyu violation unless in a current #include.
   if (ContainsKey(actual_includes, use->suggested_header())) {
     VERRS(6) << "Ignoring full use of " << use->symbol_name()
              << " (" << use->PrintableUseLoc() << "): #including dfn from "
@@ -1518,7 +1544,7 @@ void IwyuFileInfo::CalculateIwyuViolations(vector<OneUse>* uses) {
 
   // (C2) + (C3) Find the minimal 'set cover' for all symbol uses.
   const set<string> desired_set_cover = internal::CalculateMinimalIncludes(
-      direct_includes(), associated_direct_includes, uses);
+      quoted_file_, direct_includes(), associated_direct_includes, uses);
 
   // (C4) Remove .cc files from desired-includes unless they're in actual-inc.
   for (const string& header_name : desired_set_cover) {
@@ -1545,7 +1571,8 @@ void IwyuFileInfo::CalculateIwyuViolations(vector<OneUse>* uses) {
           &use, effective_direct_includes, effective_desired_includes,
           AssociatedFileEntries());
     } else {
-      internal::CalculateIwyuForFullUse(&use, effective_direct_includes);
+      internal::CalculateIwyuForFullUse(
+          &use, effective_direct_includes, quoted_file_);
     }
   }
 }

run_iwyu_tests.py

@@ -72,6 +72,7 @@ class OneIwyuTest(unittest.TestCase):
       'keep_mapping.cc': [self.CheckAlsoExtension('-public.h'), 
                           self.MappingFile('keep_mapping.imp')],
       'macro_location.cc': [self.CheckAlsoExtension('-d2.h')],
+      'mapping_to_self.cc': [self.MappingFile('mapping_to_self.imp')],
       'non_transitive_include.cc': [self.CheckAlsoExtension('-d*.h'),
                                     '--transitive_includes_only'],
       'no_h_includes_cc.cc': [self.CheckAlsoExtension('.c')],
@@ -156,6 +157,7 @@ class OneIwyuTest(unittest.TestCase):
       'lateparsed_template.cc': ['.'],
       'macro_defined_by_includer.cc': ['.'],
       'macro_location.cc': ['.'],
+      'mapping_to_self.cc': ['.'],
       'member_expr.cc': ['.'],
       'multiple_include_paths.cc': ['.'],
       'new_header_path_provided.cc': ['.'],

tests/cxx/mapping_to_self-d1.h

@@ -0,0 +1,15 @@
+//===--- mapping_to_self-d1.h - test input file for iwyu ------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef INCLUDE_WHAT_YOU_USE_TESTS_CXX_MAPPING_TO_SELF_D1_H_
+#define INCLUDE_WHAT_YOU_USE_TESTS_CXX_MAPPING_TO_SELF_D1_H_
+
+#include "tests/cxx/mapping_to_self-i1.h"
+
+#endif // INCLUDE_WHAT_YOU_USE_TESTS_CXX_MAPPING_TO_SELF_D1_H_

tests/cxx/mapping_to_self-i1.h

@@ -0,0 +1,15 @@
+//===--- mapping_to_self-i1.h - test input file for iwyu ------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef INCLUDE_WHAT_YOU_USE_TESTS_CXX_MAPPING_TO_SELF_I1_H_
+#define INCLUDE_WHAT_YOU_USE_TESTS_CXX_MAPPING_TO_SELF_I1_H_
+
+enum E {};
+
+#endif // INCLUDE_WHAT_YOU_USE_TESTS_CXX_MAPPING_TO_SELF_I1_H_

tests/cxx/mapping_to_self.cc

@@ -0,0 +1,16 @@
+//===--- mapping_to_self.cc - test input file for iwyu --------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "tests/cxx/mapping_to_self.h"
+
+/**** IWYU_SUMMARY
+
+(tests/cxx/mapping_to_self.cc has correct #includes/fwd-decls)
+
+***** IWYU_SUMMARY */

tests/cxx/mapping_to_self.h

@@ -0,0 +1,26 @@
+//===--- mapping_to_self.h - test input file for iwyu ---------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef INCLUDE_WHAT_YOU_USE_TESTS_CXX_MAPPING_TO_SELF_H_
+#define INCLUDE_WHAT_YOU_USE_TESTS_CXX_MAPPING_TO_SELF_H_
+
+#include "tests/cxx/mapping_to_self-d1.h" // IWYU pragma: keep
+
+// A mapping is defined from E to this file.  This test is to ensure that
+// - That mapping is selected over another mapping.
+// - The mapping does not force this file to add a #include of itself.
+E e;
+
+#endif // INCLUDE_WHAT_YOU_USE_TESTS_CXX_MAPPING_TO_SELF_H_
+
+/**** IWYU_SUMMARY
+
+(tests/cxx/mapping_to_self.h has correct #includes/fwd-decls)
+
+***** IWYU_SUMMARY */

tests/cxx/mapping_to_self.imp

@@ -0,0 +1,4 @@
+[
+  { symbol: ["E", "private", "\"tests/cxx/some_other_header.h\"", "public"] },
+  { symbol: ["E", "private", "\"tests/cxx/mapping_to_self.h\"", "public"] }
+]