pathPatternParser.h

//
// Copyright 2024 Pixar
//
// Licensed under the terms set forth in the LICENSE.txt file available at
// https://openusd.org/license.
//
 
#ifndef PXR_USD_SDF_PATH_PATTERN_PARSER_H
#define PXR_USD_SDF_PATH_PATTERN_PARSER_H
 
#include "pxr/pxr.h"
 
#include "pxr/usd/sdf/predicateExpressionParser.h"
#include "pxr/base/pegtl/pegtl.hpp"
 
#include <memory>
 
PXR_NAMESPACE_OPEN_SCOPE
 
namespace SdfPathPatternParser {
 
using namespace PXR_PEGTL_NAMESPACE;
 
template <class Rule> using OptSpaced = pad<Rule, blank>;
 
// Path patterns with predicates.
struct PathPatStretch : two<'/'> {};
struct PathPatSep : sor<PathPatStretch, one<'/'>> {};
 
// Named close rules so the Errors class can attach targeted messages.
struct PredExprClose     : one<'}'> {};
struct BracketClassClose : one<']'> {};
 
// '{' commits to requiring a predicate expression and a closing '}'.
// PredExprClose is named so the Errors class can target it specifically.
struct BracedPredExpr
    : if_must<one<'{'>,
              OptSpaced<SdfPredicateExpressionParser::PredExpr>,
              PredExprClose> {};
 
// '[' commits to requiring valid content and a closing ']'.
struct BracketClass :
    if_must<one<'['>,
            plus<sor<identifier_other, one<'!','-','?','*'>>>,
            BracketClassClose> {};
 
struct PrimPathWildCard :
    plus<sor<BracketClass, identifier_other, one<'?','*'>>> {};
 
struct PropPathWildCard :
    plus<sor<BracketClass, identifier_other, one<':','?','*'>>> {};
 
struct PrimPathPatternElemText : PrimPathWildCard {};
struct PropPathPatternElemText : PropPathWildCard {};
 
struct PrimPathPatternElem
    : if_then_else<PrimPathPatternElemText, opt<BracedPredExpr>,
                   BracedPredExpr> {};
 
struct PropPathPatternElem
    : if_then_else<PropPathPatternElemText, opt<BracedPredExpr>,
                   BracedPredExpr> {};
 
// A single '/' that is not the start of '//'. Used as a commitment point:
// once matched, a path pattern element is unconditionally required.
struct PatSepSlash : seq<one<'/'>, not_at<one<'/'>>> {};
 
// PatSepSlash commits to requiring a following prim pattern element.
struct PrimPatStep : if_must<PatSepSlash, PrimPathPatternElem> {};
 
// '//' as separator, but only when a prim element immediately follows.
// Trailing '//' without a following element falls through to
// opt<PathPatStretch> at the end of PathPatternElems.  Note: the lookahead
// parses PathPatStretch+PrimPathPatternElem twice; acceptable given the bounded
// syntax involved.
struct StretchStep : seq<
    at<seq<PathPatStretch, PrimPathPatternElem>>,
    PathPatStretch,
    PrimPathPatternElem> {};
 
struct PathPatternElems
    : seq<PrimPathPatternElem,
          star<sor<StretchStep, PrimPatStep>>,
          if_must_else<one<'.'>, PropPathPatternElem, opt<PathPatStretch>>> {};
 
struct AbsPathPattern : seq<PathPatSep, opt<PathPatternElems>> {};
 
struct DotDot  : two<'.'> {};
struct DotDots : list<DotDot, one<'/'>> {};
 
struct ReflexiveRelative : one<'.'> {};
 
struct AbsoluteStart : at<one<'/'>> {};
 
// After DotDots, single '/' commits to requiring pattern elements.  '//'
// retains optional-elements behavior since a bare '..//' (stretch from ancestor
// context) is a valid pattern with no following elements.
struct DotDotsStep        : if_must<PatSepSlash, PathPatternElems> {};
struct DotDotsStretchTail : seq<PathPatStretch, opt<PathPatternElems>> {};
 
struct PathPattern :
    sor<
    if_must<AbsoluteStart, AbsPathPattern>,
    seq<DotDots, opt<sor<DotDotsStretchTail, DotDotsStep>>>,
    PathPatternElems,
    seq<ReflexiveRelative, opt<PathPatStretch, opt<PathPatternElems>>>
    >
{};
 
// Errors.
//
// Inherits from SdfPredicateExpressionParser::Errors so predicate rule errors
// propagate automatically without re-listing them here. Only
// path-pattern-specific rules need PARSE_ERROR entries.
//
// The struct-override macro is used (rather than a message pointer) because the
// derived Errors class has no message member of its own -- it uses the base's
// raise() for inherited rules and overrides raise() directly for local ones.
 
template <class Rule>
struct Errors : SdfPredicateExpressionParser::Errors<Rule> {};
 
#define PARSE_ERROR(rule, msg)                                              \
    template <> struct Errors<rule>                                         \
        : SdfPredicateExpressionParser::Errors<rule> {                      \
        template <class Input, class... States>                             \
        [[noreturn]] static void raise(Input const &in, States &&...) {     \
            throw parse_error(msg, in);                                     \
        }                                                                   \
    }
 
PARSE_ERROR(PrimPathPatternElem, "expected path pattern element");
PARSE_ERROR(PathPatternElems,    "expected path pattern element after '/'");
PARSE_ERROR(PropPathPatternElem, "expected property pattern element after '.'");
PARSE_ERROR(PredExprClose,       "expected '}' to close predicate expression");
PARSE_ERROR(BracketClassClose,   "expected ']' to close bracket class");
 
#undef PARSE_ERROR
 
} // SdfPathPatternParser
 
 
namespace SdfPathPatternActions {
 
using namespace PXR_PEGTL_NAMESPACE;
 
using namespace SdfPathPatternParser;
 
// Actions /////////////////////////////////////////////////////////////
 
struct PatternBuilder
{
    // The final resulting pattern winds up here.
    SdfPathPattern pattern;
 
    // These are used during parsing.
    std::string curElemText;
    SdfPredicateExpression curPredExpr;
};
 
 
template <class Rule>
struct PathPatternAction : nothing<Rule> {};
 
template <>
struct PathPatternAction<AbsoluteStart>
{
    template <class Input>
    static void apply(Input const &in, PatternBuilder &builder) {
        builder.pattern.SetPrefix(SdfPath::AbsoluteRootPath());
    }
};
 
template <>
struct PathPatternAction<PathPatStretch>
{
    template <class Input>
    static void apply(Input const &in, PatternBuilder &builder) {
        // '//' appends a component representing arbitrary hierarchy.
        TF_VERIFY(builder.pattern.AppendStretchIfPossible());
    }
};
 
// Change action & state to the PredicateExpressionParser so it can parse &
// build a predicate expression for us.
template <>
struct PathPatternAction<SdfPredicateExpressionParser::PredExpr>
    : change_action_and_states<SdfPredicateExpressionParser::PredAction,
                               SdfPredicateExprBuilder>
{
    template <class Input>
    static void success(Input const &in,
                        SdfPredicateExprBuilder &predExprBuilder,
                        PatternBuilder &builder) {
        builder.curPredExpr = predExprBuilder.Finish();
    }
};
 
template <>
struct PathPatternAction<PrimPathPatternElemText>
{
    template <class Input>
    static void apply(Input const &in, PatternBuilder &builder) {
        builder.curElemText = in.string();
    }
};
 
template <>
struct PathPatternAction<PropPathPatternElemText>
{
    template <class Input>
    static void apply(Input const &in, PatternBuilder &builder) {
        builder.curElemText = in.string();
    }
};
 
template <>
struct PathPatternAction<PrimPathPatternElem>
{
    template <class Input>
    static void apply(Input const &in, PatternBuilder &builder) {
        builder.pattern.AppendChild(builder.curElemText, builder.curPredExpr);
        builder.curElemText.clear();
        builder.curPredExpr = SdfPredicateExpression();
    }
};
 
template <>
struct PathPatternAction<PropPathPatternElem>
{
    template <class Input>
    static void apply(Input const &in, PatternBuilder &builder) {
        builder.pattern.AppendProperty(builder.curElemText,
                                       builder.curPredExpr);
        builder.curElemText.clear();
        builder.curPredExpr = SdfPredicateExpression();
    }
};
 
template <>
struct PathPatternAction<ReflexiveRelative>
{
    template <class Input>
    static void apply(Input const &in, PatternBuilder &builder) {
        builder.pattern.SetPrefix(SdfPath::ReflexiveRelativePath());
    }
};
 
template <>
struct PathPatternAction<DotDot>
{
    template <class Input>
    static void apply(Input const &in, PatternBuilder &builder) {
        builder.pattern.AppendChild("..");
    }
};
 
} // SdfPathPatternActions
 
PXR_NAMESPACE_CLOSE_SCOPE
 
#endif // PXR_USD_SDF_PATH_PATTERN_PARSER_H