demangle: parse C++20 subobjects in expressions

Author: ianlancetaylor

ast.go

@@ -2476,6 +2476,79 @@ func (f *Fold) goString(indent int, field string) string {
 	}
 }
 
+// Subobject is a a reference to an offset in an expression.  This is
+// used for C++20 manglings of class types used as the type of
+// non-type template arguments.
+//
+// See https://github.com/itanium-cxx-abi/cxx-abi/issues/47.
+type Subobject struct {
+	Type      AST
+	SubExpr   AST
+	Offset    int
+	Selectors []int
+	PastEnd   bool
+}
+
+func (so *Subobject) print(ps *printState) {
+	ps.print(so.SubExpr)
+	ps.writeString(".<")
+	ps.print(so.Type)
+	ps.writeString(fmt.Sprintf(" at offset %d>", so.Offset))
+}
+
+func (so *Subobject) Traverse(fn func(AST) bool) {
+	if fn(so) {
+		so.Type.Traverse(fn)
+		so.SubExpr.Traverse(fn)
+	}
+}
+
+func (so *Subobject) Copy(fn func(AST) AST, skip func(AST) bool) AST {
+	if skip(so) {
+		return nil
+	}
+	typ := so.Type.Copy(fn, skip)
+	subExpr := so.SubExpr.Copy(fn, skip)
+	if typ == nil && subExpr == nil {
+		return nil
+	}
+	if typ == nil {
+		typ = so.Type
+	}
+	if subExpr == nil {
+		subExpr = so.SubExpr
+	}
+	so = &Subobject {
+		Type:      typ,
+		SubExpr:   subExpr,
+		Offset:    so.Offset,
+		Selectors: so.Selectors,
+		PastEnd:   so.PastEnd,
+	}
+	if r := fn(so); r != nil {
+		return r
+	}
+	return so
+}
+
+func (so *Subobject) GoString() string {
+	return so.goString(0, "")
+}
+
+func (so *Subobject) goString(indent int, field string) string {
+	var selectors string
+	for _, s := range so.Selectors {
+		selectors += fmt.Sprintf(" %d", s)
+	}
+	return fmt.Sprintf("%*s%sSubobject:\n%s\n%s\n%*sOffset: %d\n%*sSelectors:%s\n%*sPastEnd: %t",
+		indent, "", field,
+		so.Type.goString(indent+2, "Type: "),
+		so.SubExpr.goString(indent+2, "SubExpr: "),
+		indent+2, "", so.Offset,
+		indent+2, "", selectors,
+		indent+2, "", so.PastEnd)
+}
+
 // New is a use of operator new in an expression.
 type New struct {
 	Op    AST

cases_test.go

@@ -30177,10 +30177,7 @@ var casesExpectedFailures = map[string]bool{
 	"_ZN1XIZ1fIiEvOT_EUlS2_DpT0_E_EclIJEEEvDpT_":                                                    true,
 	"_ZZZZN6abcdef9abcdefghi29abcdefabcdefabcdefabcefabcdef27xxxxxxxxxxxxxxxxxxxxxxxxxxxEN4absl8DurationERKNSt3__u12basic_stringIcNS4_11char_traitsIcEENS4_9allocatorIcEEEEPNS1_19yyyyyyyyyyyyyyyyyyyEENK3$_5clEvENKUlvE_clEvE6zzzzzz": true,
 	"_Z1fIXtl1BadsoiL_Z6nestedE_EEEEvv":                      true,
-	"_Z1fIXtl1BadsoiL_Z6nestedE16_0pEEEEvv":                  true,
-	"_Z1fIXtl2BRsoiL_Z7derivedE4EEEEvv":                      true,
 	"_Z1fIXtl1BcvPiplcvPcadL_Z7derivedELl16EEEEvv":           true,
-	"_Z1fIXtl1CadsoKiL_Z7derivedE4EEEEvv":                    true,
 	"_Z1fIXtl1DmcM7DerivedKiadL_ZN11MoreDerived1zEEn8EEEEvv": true,
 	"_Z1fIXtl1Edi1nLi42EEEEvv":                               true,
 	"_Z1h1XIJZ1fIiEDaOT_E1AZ1gIdEDaS2_E1BEE":                 true,

demangle.go

@@ -1971,6 +1971,7 @@ func (st *state) exprList(stop byte) AST {
 //              ::= rc <type> <expression>
 //              ::= ti <type>
 //              ::= te <expression>
+//              ::= so <referent type> <expr> [<offset number>] <union-selector>* [p] E
 //              ::= st <type>
 //              ::= sz <expression>
 //              ::= at <type>
@@ -2013,6 +2014,9 @@ func (st *state) expression() AST {
 		return st.exprPrimary()
 	} else if st.str[0] == 'T' {
 		return st.templateParam()
+	} else if st.str[0] == 's' && len(st.str) > 1 && st.str[1] == 'o' {
+		st.advance(2)
+		return st.subobject()
 	} else if st.str[0] == 's' && len(st.str) > 1 && st.str[1] == 'r' {
 		return st.unresolvedName()
 	} else if st.str[0] == 's' && len(st.str) > 1 && st.str[1] == 'p' {
@@ -2185,6 +2189,39 @@ func (st *state) expression() AST {
 	}
 }
 
+// <expression> ::= so <referent type> <expr> [<offset number>] <union-selector>* [p] E
+// <union-selector> ::= _ [<number>]
+func (st *state) subobject() AST {
+	typ := st.demangleType(false)
+	expr := st.expression()
+	offset := 0
+	if len(st.str) > 0 && (st.str[0] == 'n' || isDigit(st.str[0])) {
+		offset = st.number()
+	}
+	var selectors []int
+	for len(st.str) > 0 && st.str[0] == '_' {
+		st.advance(1)
+		selector := st.number()
+		selectors = append(selectors, selector)
+	}
+	pastEnd := false
+	if len(st.str) > 0 && st.str[0] == 'p' {
+		st.advance(1)
+		pastEnd = true
+	}
+	if len(st.str) == 0 || st.str[0] != 'E' {
+		st.fail("expected E after subobject")
+	}
+	st.advance(1)
+	return &Subobject{
+		Type:      typ,
+		SubExpr:   expr,
+		Offset:    offset,
+		Selectors: selectors,
+		PastEnd:   pastEnd,
+	}
+}
+
 // <unresolved-name> ::= [gs] <base-unresolved-name>
 //                   ::= sr <unresolved-type> <base-unresolved-name>
 //                   ::= srN <unresolved-type> <unresolved-qualifier-level>+ E <base-unresolved-name>