[all-commits] [llvm/llvm-project] bd5cc6: [pseudo] Start rules are `_ := start-symbol EOF`, ...

Sam McCall via All-commits all-commits at lists.llvm.org
Fri Aug 19 07:50:22 PDT 2022

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: bd5cc6575bdbe1d091f1cc70fb7f0b3c07cb894b
  Author: Sam McCall <sam.mccall at gmail.com>
  Date:   2022-08-19 (Fri, 19 Aug 2022)

  Changed paths:
    M clang-tools-extra/pseudo/include/clang-pseudo/GLR.h
    M clang-tools-extra/pseudo/lib/Forest.cpp
    M clang-tools-extra/pseudo/lib/GLR.cpp
    M clang-tools-extra/pseudo/lib/cxx/cxx.bnf
    M clang-tools-extra/pseudo/lib/grammar/LRGraph.cpp
    M clang-tools-extra/pseudo/test/lr-build-basic.test
    M clang-tools-extra/pseudo/test/lr-build-conflicts.test
    M clang-tools-extra/pseudo/unittests/ForestTest.cpp
    M clang-tools-extra/pseudo/unittests/GLRTest.cpp

  Log Message:
  [pseudo] Start rules are `_ := start-symbol EOF`, improve recovery.

Previously we were calling glrRecover() ad-hoc at the end of input.
Two main problems with this:
 - glrRecover() on two separate code paths is inelegant
 - We may have to recover several times in succession (e.g. to exit from
   nested scopes), so we need a loop at end-of-file
Having an actual shift action for an EOF terminal allows us to handle
both concerns in the main shift/recover/reduce loop.

This revealed a recovery design bug where recovery could enter a loop by
repeatedly choosing the same parent to identically recover from.
Addressed this by allowing each node to be used as a recovery base once.

Differential Revision: https://reviews.llvm.org/D130550

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