[AST][JSON] Fix null ptr crash dumping TemplateTemplateParmDecl

[dtolnay]

Summary

The following program winds up with D->getDefaultArgStorage().getInheritedFrom() == nullptr
during dumping the TemplateTemplateParmDecl corresponding to the template parameter of i.

template <typename>
struct R;
template <template <typename> class = R>
void i();

Previously--

 #6 clang::TemplateTemplateParmDecl::getSourceRange() const clang/include/clang/AST/DeclTemplate.h:1745
#15 clang::JSONNodeDumper::VisitTemplateTemplateParmDecl(clang::TemplateTemplateParmDecl const*) clang/lib/AST/JSONNodeDumper.cpp:889
#16 clang::JSONNodeDumper::Visit(clang::Decl const*) clang/lib/AST/JSONNodeDumper.cpp:128
...
clang-13: error: unable to execute command: Segmentation fault (core dumped)

[aaron.ballman]

LGTM, thank you for the fix! Do you need me to commit on your behalf? If so, what email address and name would you like me to use for attribution?

[dtolnay]

Yes, could you please commit for me? This is my first contribution. Please attribute to David Tolnay <[e-mail]>.

[aaron.ballman]

In D101212#2714697, @dtolnay wrote:

Yes, could you please commit for me? This is my first contribution. Please attribute to David Tolnay <[e-mail]>.

I've committed on your behalf in 967ebad12521f3187014a722804c27a75d44e649. Congrats on landing your first contribution!

clang/lib/AST/JSONNodeDumper.cpp

 #include "clang/AST/JSONNodeDumper.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/Specifiers.h"
 #include "clang/Lex/Lexer.h"
 #include "llvm/ADT/StringSwitch.h"
 
 using namespace clang;
 
void JSONNodeDumper::VisitTemplateTemplateParmDecl(
     const TemplateTemplateParmDecl *D) {
   VisitNamedDecl(D);
   JOS.attribute("depth", D->getDepth());
   JOS.attribute("index", D->getIndex());
   attributeOnlyIfTrue("isParameterPack", D->isParameterPack());
 
   if (D->hasDefaultArgument())
     JOS.attributeObject("defaultArg", [=] {
+      const auto *InheritedFrom = D->getDefaultArgStorage().getInheritedFrom();
       Visit(D->getDefaultArgument().getArgument(),
-            D->getDefaultArgStorage().getInheritedFrom()->getSourceRange(),
-            D->getDefaultArgStorage().getInheritedFrom(),
+            InheritedFrom ? InheritedFrom->getSourceRange() : SourceLocation{},
+            InheritedFrom,
             D->defaultArgumentWasInherited() ? "inherited from" : "previous");
     });
 }
 
 void JSONNodeDumper::VisitLinkageSpecDecl(const LinkageSpecDecl *LSD) {
   StringRef Lang;
   switch (LSD->getLanguage()) {
   case LinkageSpecDecl::lang_c: Lang = "C"; break;

clang/test/AST/ast-dump-template-decls-json.cpp

struct V {
   template <typename Uy>
   void f();
 };
 
 template <typename Ty>
 template <typename Uy>
 void V<Ty>::f() {}
 
+template <template <typename> class = R>
+void i();
+
 // NOTE: CHECK lines have been autogenerated by gen_ast_dump_json_test.py
 
 
 // CHECK:  "kind": "TranslationUnitDecl",
 // CHECK-NEXT:  "loc": {},
 // CHECK-NEXT:  "range": {
 // CHECK-NEXT:   "begin": {},
 // CHECK-NEXT:   "end": {}

 // CHECK-NEXT:          "col": 18,
 // CHECK-NEXT:          "tokLen": 1
 // CHECK-NEXT:         }
 // CHECK-NEXT:        }
 // CHECK-NEXT:       }
 // CHECK-NEXT:      ]
 // CHECK-NEXT:     }
 // CHECK-NEXT:    ]
+// CHECK-NEXT:   },
+// CHECK-NEXT:   {
+// CHECK-NEXT:    "id": "0x{{.*}}",
+// CHECK-NEXT:    "kind": "FunctionTemplateDecl",
+// CHECK-NEXT:    "loc": {
+// CHECK-NEXT:     "offset": 922,
+// CHECK-NEXT:     "line": 59,
+// CHECK-NEXT:     "col": 6,
+// CHECK-NEXT:     "tokLen": 1
+// CHECK-NEXT:    },
+// CHECK-NEXT:    "range": {
+// CHECK-NEXT:     "begin": {
+// CHECK-NEXT:      "offset": 876,
+// CHECK-NEXT:      "line": 58,
+// CHECK-NEXT:      "col": 1,
+// CHECK-NEXT:      "tokLen": 8
+// CHECK-NEXT:     },
+// CHECK-NEXT:     "end": {
+// CHECK-NEXT:      "offset": 924,
+// CHECK-NEXT:      "line": 59,
+// CHECK-NEXT:      "col": 8,
+// CHECK-NEXT:      "tokLen": 1
+// CHECK-NEXT:     }
+// CHECK-NEXT:    },
+// CHECK-NEXT:    "name": "i",
+// CHECK-NEXT:    "inner": [
+// CHECK-NEXT:     {
+// CHECK-NEXT:      "id": "0x{{.*}}",
+// CHECK-NEXT:      "kind": "TemplateTemplateParmDecl",
+// CHECK-NEXT:      "loc": {
+// CHECK-NEXT:       "offset": 912,
+// CHECK-NEXT:       "line": 58,
+// CHECK-NEXT:       "col": 37,
+// CHECK-NEXT:       "tokLen": 1
+// CHECK-NEXT:      },
+// CHECK-NEXT:      "range": {
+// CHECK-NEXT:       "begin": {
+// CHECK-NEXT:        "offset": 886,
+// CHECK-NEXT:        "col": 11,
+// CHECK-NEXT:        "tokLen": 8
+// CHECK-NEXT:       },
+// CHECK-NEXT:       "end": {
+// CHECK-NEXT:        "offset": 914,
+// CHECK-NEXT:        "col": 39,
+// CHECK-NEXT:        "tokLen": 1
+// CHECK-NEXT:       }
+// CHECK-NEXT:      },
+// CHECK-NEXT:      "depth": 0,
+// CHECK-NEXT:      "index": 0,
+// CHECK-NEXT:      "defaultArg": {
+// CHECK-NEXT:       "kind": "TemplateArgument"
+// CHECK-NEXT:      },
+// CHECK-NEXT:      "inner": [
+// CHECK-NEXT:       {
+// CHECK-NEXT:        "id": "0x{{.*}}",
+// CHECK-NEXT:        "kind": "TemplateTypeParmDecl",
+// CHECK-NEXT:        "loc": {
+// CHECK-NEXT:         "offset": 904,
+// CHECK-NEXT:         "col": 29,
+// CHECK-NEXT:         "tokLen": 1
+// CHECK-NEXT:        },
+// CHECK-NEXT:        "range": {
+// CHECK-NEXT:         "begin": {
+// CHECK-NEXT:          "offset": 896,
+// CHECK-NEXT:          "col": 21,
+// CHECK-NEXT:          "tokLen": 8
+// CHECK-NEXT:         },
+// CHECK-NEXT:         "end": {
+// CHECK-NEXT:          "offset": 896,
+// CHECK-NEXT:          "col": 21,
+// CHECK-NEXT:          "tokLen": 8
+// CHECK-NEXT:         }
+// CHECK-NEXT:        },
+// CHECK-NEXT:        "tagUsed": "typename",
+// CHECK-NEXT:        "depth": 1,
+// CHECK-NEXT:        "index": 0
+// CHECK-NEXT:       },
+// CHECK-NEXT:       {
+// CHECK-NEXT:        "kind": "TemplateArgument",
+// CHECK-NEXT:        "range": {
+// CHECK-NEXT:         "begin": {
+// CHECK-NEXT:          "offset": 914,
+// CHECK-NEXT:          "col": 39,
+// CHECK-NEXT:          "tokLen": 1
+// CHECK-NEXT:         },
+// CHECK-NEXT:         "end": {
+// CHECK-NEXT:          "offset": 914,
+// CHECK-NEXT:          "col": 39,
+// CHECK-NEXT:          "tokLen": 1
+// CHECK-NEXT:         }
+// CHECK-NEXT:        }
+// CHECK-NEXT:       }
+// CHECK-NEXT:      ]
+// CHECK-NEXT:     },
+// CHECK-NEXT:     {
+// CHECK-NEXT:      "id": "0x{{.*}}",
+// CHECK-NEXT:      "kind": "FunctionDecl",
+// CHECK-NEXT:      "loc": {
+// CHECK-NEXT:       "offset": 922,
+// CHECK-NEXT:       "line": 59,
+// CHECK-NEXT:       "col": 6,
+// CHECK-NEXT:       "tokLen": 1
+// CHECK-NEXT:      },
+// CHECK-NEXT:      "range": {
+// CHECK-NEXT:       "begin": {
+// CHECK-NEXT:        "offset": 917,
+// CHECK-NEXT:        "col": 1,
+// CHECK-NEXT:        "tokLen": 4
+// CHECK-NEXT:       },
+// CHECK-NEXT:       "end": {
+// CHECK-NEXT:        "offset": 924,
+// CHECK-NEXT:        "col": 8,
+// CHECK-NEXT:        "tokLen": 1
+// CHECK-NEXT:       }
+// CHECK-NEXT:      },
+// CHECK-NEXT:      "name": "i",
+// CHECK-NEXT:      "type": {
+// CHECK-NEXT:       "qualType": "void ()"
+// CHECK-NEXT:      }
+// CHECK-NEXT:     }
+// CHECK-NEXT:    ]
 // CHECK-NEXT:   }
 // CHECK-NEXT:  ]
 // CHECK-NEXT: }