| //===--- Disambiguate.h - Find the best tree in the forest -------*- C++-*-===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // A GLR parse forest represents every possible parse tree for the source code. |
| // |
| // Before we can do useful analysis/editing of the code, we need to pick a |
| // single tree which we think is accurate. We use three main types of clues: |
| // |
| // A) Semantic language rules may restrict which parses are allowed. |
| // For example, `string string string X` is *grammatical* C++, but only a |
| // single type-name is allowed in a decl-specifier-sequence. |
| // Where possible, these interpretations are forbidden by guards. |
| // Sometimes this isn't possible, or we want our parser to be lenient. |
| // |
| // B) Some constructs are rarer, while others are common. |
| // For example `a<b>::c` is often a template specialization, and rarely a |
| // double comparison between a, b, and c. |
| // |
| // C) Identifier text hints whether they name types/values/templates etc. |
| // "std" is usually a namespace, a project index may also guide us. |
| // Hints may be within the document: if one occurrence of 'foo' is a variable |
| // then the others probably are too. |
| // (Text need not match: similar CaseStyle can be a weak hint, too). |
| // |
| //----------------------------------------------------------------------------// |
| // |
| // Mechanically, we replace each ambiguous node with its best alternative. |
| // |
| // "Best" is determined by assigning bonuses/penalties to nodes, to express |
| // the clues of type A and B above. A forest node representing an unlikely |
| // parse would apply a penalty to every subtree is is present in. |
| // Disambiguation proceeds bottom-up, so that the score of each alternative |
| // is known when a decision is made. |
| // |
| // Identifier-based hints within the document mean some nodes should be |
| // *correlated*. Rather than resolve these simultaneously, we make the most |
| // certain decisions first and use these results to update bonuses elsewhere. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "clang-pseudo/Forest.h" |
| |
| namespace clang::pseudo { |
| |
| struct DisambiguateParams {}; |
| |
| // Maps ambiguous nodes onto the index of their preferred alternative. |
| using Disambiguation = llvm::DenseMap<const ForestNode *, unsigned>; |
| |
| // Resolve each ambiguous node in the forest. |
| // Maps each ambiguous node to the index of the chosen alternative. |
| // FIXME: current implementation is a placeholder and chooses arbitrarily. |
| Disambiguation disambiguate(const ForestNode *Root, |
| const DisambiguateParams &Params); |
| |
| // Remove all ambiguities from the forest, resolving them according to Disambig. |
| void removeAmbiguities(ForestNode *&Root, const Disambiguation &Disambig); |
| |
| } // namespace clang::pseudo |
