clang-tools-extra/clangd/HeuristicResolver.h

   1 //===--- HeuristicResolver.h - Resolution of dependent names -----*- C++-*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_HEURISTICRESOLVER_H
  10 #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_HEURISTICRESOLVER_H
  11
  12 #include "clang/AST/Decl.h"
  13 #include <vector>
  14
  15 namespace clang {
  16
  17 class ASTContext;
  18 class CallExpr;
  19 class CXXDependentScopeMemberExpr;
  20 class DeclarationName;
  21 class DependentScopeDeclRefExpr;
  22 class NamedDecl;
  23 class Type;
  24 class UnresolvedUsingValueDecl;
  25
  26 namespace clangd {
  27
  28 // This class heuristic resolution of declarations and types in template code.
  29 //
  30 // As a compiler, clang only needs to perform certain types of processing on
  31 // template code (such as resolving dependent names to declarations, or
  32 // resolving the type of a dependent expression) after instantiation. Indeed,
  33 // C++ language features such as template specialization mean such resolution
  34 // cannot be done accurately before instantiation
  35 //
  36 // However, template code is written and read in uninstantiated form, and clangd
  37 // would like to provide editor features like go-to-definition in template code
  38 // where possible. To this end, clangd attempts to resolve declarations and
  39 // types in uninstantiated code by using heuristics, understanding that the
  40 // results may not be fully accurate but that this is better than nothing.
  41 //
  42 // At this time, the heuristic used is a simple but effective one: assume that
  43 // template instantiations are based on the primary template definition and not
  44 // not a specialization. More advanced heuristics may be added in the future.
  45 class HeuristicResolver {
  46 public:
  47   HeuristicResolver(ASTContext &Ctx) : Ctx(Ctx) {}
  48
  49   // Try to heuristically resolve certain types of expressions, declarations, or
  50   // types to one or more likely-referenced declarations.
  51   std::vector<const NamedDecl *>
  52   resolveMemberExpr(const CXXDependentScopeMemberExpr *ME) const;
  53   std::vector<const NamedDecl *>
  54   resolveDeclRefExpr(const DependentScopeDeclRefExpr *RE) const;
  55   std::vector<const NamedDecl *>
  56   resolveTypeOfCallExpr(const CallExpr *CE) const;
  57   std::vector<const NamedDecl *>
  58   resolveCalleeOfCallExpr(const CallExpr *CE) const;
  59   std::vector<const NamedDecl *>
  60   resolveUsingValueDecl(const UnresolvedUsingValueDecl *UUVD) const;
  61   std::vector<const NamedDecl *>
  62   resolveDependentNameType(const DependentNameType *DNT) const;
  63   std::vector<const NamedDecl *> resolveTemplateSpecializationType(
  64       const DependentTemplateSpecializationType *DTST) const;
  65
  66   // Try to heuristically resolve a dependent nested name specifier
  67   // to the type it likely denotes. Note that *dependent* name specifiers always
  68   // denote types, not namespaces.
  69   const Type *
  70   resolveNestedNameSpecifierToType(const NestedNameSpecifier *NNS) const;
  71
  72   // Given the type T of a dependent expression that appears of the LHS of a
  73   // "->", heuristically find a corresponding pointee type in whose scope we
  74   // could look up the name appearing on the RHS.
  75   const Type *getPointeeType(const Type *T) const;
  76
  77 private:
  78   ASTContext &Ctx;
  79
  80   // Given a tag-decl type and a member name, heuristically resolve the
  81   // name to one or more declarations.
  82   // The current heuristic is simply to look up the name in the primary
  83   // template. This is a heuristic because the template could potentially
  84   // have specializations that declare different members.
  85   // Multiple declarations could be returned if the name is overloaded
  86   // (e.g. an overloaded method in the primary template).
  87   // This heuristic will give the desired answer in many cases, e.g.
  88   // for a call to vector<T>::size().
  89   std::vector<const NamedDecl *> resolveDependentMember(
  90       const Type *T, DeclarationName Name,
  91       llvm::function_ref<bool(const NamedDecl *ND)> Filter) const;
  92
  93   // Try to heuristically resolve the type of a possibly-dependent expression
  94   // `E`.
  95   const Type *resolveExprToType(const Expr *E) const;
  96   std::vector<const NamedDecl *> resolveExprToDecls(const Expr *E) const;
  97 };
  98
  99 } // namespace clangd
 100 } // namespace clang
 101
 102 #endif