[include-fixer] Be smarter about inserting symbols for a prefix.

[bkramer]

Summary

If prefix search finds something where nothing can be nested under (e.g.
a variable or macro) don't add it to the result.

This is for cases like:
header.h:

extern int a;

file.cc:
namespace a {

SOME_MACRO

}

We will look up a::SOME_MACRO, which doesn't have any results. Then we
look up 'a' and find something before we ever look up just 'SOME_MACRO'.
With some basic filtering we can avoid this case.

[ioeric]

LG.

include-fixer/SymbolIndexManager.cpp

if (Identifier.startswith("::")) {
     Names.erase(Names.begin()); // Drop first (empty) element.
     IsFullyQualified = true;
   }
 
   // As long as we don't find a result keep stripping name parts from the end.
   // This is to support nested classes which aren't recorded in the database.
   // Eventually we will either hit a class (namespaces aren't in the database
   // either) and can report that result.
+  bool TookPrefix = false;
   std::vector<std::string> Results;
   while (Results.empty() && !Names.empty()) {
     std::vector<clang::find_all_symbols::SymbolInfo> Symbols;
     for (const auto &DB : SymbolIndices) {
       auto Res = DB->search(Names.back().str());
       Symbols.insert(Symbols.end(), Res.begin(), Res.end());
     }
 
for (const auto &Symbol : Symbols) {
         // If the name was qualified we only want to add results if we evaluated
         // all contexts.
         if (IsFullyQualified)
           IsMatched &= (SymbolContext == Symbol.getContexts().end());
 
         // FIXME: Support full match. At this point, we only find symbols in
         // database which end with the same contexts with the identifier.
         if (IsMatched && IdentiferContext == Names.rend()) {
+          // If we're in a situation where we took a prefix but the thing we
+          // found couldn't possibly have a nested member ignore it.
+          if (TookPrefix &&
+              (Symbol.getSymbolKind() == SymbolInfo::SymbolKind::Function ||
+               Symbol.getSymbolKind() == SymbolInfo::SymbolKind::Variable ||
+               Symbol.getSymbolKind() ==
+                   SymbolInfo::SymbolKind::EnumConstantDecl ||
+               Symbol.getSymbolKind() == SymbolInfo::SymbolKind::Macro))
+            continue;
+
           // FIXME: file path should never be in the form of <...> or "...", but
           // the unit test with fixed database use <...> file path, which might
           // need to be changed.
           // FIXME: if the file path is a system header name, we want to use
           // angle brackets.
           std::string FilePath = Symbol.getFilePath().str();
           Results.push_back((FilePath[0] == '"' || FilePath[0] == '<')
                                 ? FilePath
                                 : "\"" + FilePath + "\"");
         }
       }
     }
     Names.pop_back();
+    TookPrefix = true;
   }
 
   return Results;
 }
 
 } // namespace include_fixer
 } // namespace clang

test/include-fixer/Inputs/fake_yaml_db.yaml

Contexts:
   - ContextType:     Namespace
     ContextName:     a
   - ContextType:     Namespace
     ContextName:     b
 FilePath:        ../include/zbar.h
 LineNumber:      1
 Type:            Class
 NumOccurrences:  3
+---
+Name:           b
+Contexts:
+FilePath:        var.h
+LineNumber:      1
+Type:            Variable
+NumOccurrences:  1
+...

test/include-fixer/prefix_variable.cpp

+// REQUIRES: shell
+// RUN: sed -e 's#//.*$##' %s > %t.cpp
+// RUN: clang-include-fixer -db=yaml -input=%p/Inputs/fake_yaml_db.yaml %t.cpp --
+// RUN: FileCheck %s -input-file=%t.cpp
+
+// CHECK-NOT: #include
+// CHECK: doesnotexist f;
+
+namespace b {
+doesnotexist f;
+}