[clang] [analyzer] Add std::variant checker (PR #66481)

[via cfe-commits]

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+// RUN: %clang %s -std=c++17 -Xclang -verify --analyze \
+// RUN:   -Xclang -analyzer-checker=core \
+// RUN:   -Xclang -analyzer-checker=debug.ExprInspection \
+// RUN:   -Xclang -analyzer-checker=core,alpha.core.StdVariant
+
+#include "Inputs/system-header-simulator-cxx.h"
+
+class Foo{};
+
+void clang_analyzer_warnIfReached();
+void clang_analyzer_eval(int);
+
+//helper functions
+void changeVariantType(std::variant<int, char> &v) {
+  v = 25;
+}
+
+void changesToInt(std::variant<int, char> &v);
+void changesToInt(std::variant<int, char> *v);
+
+void cannotChangePtr(const std::variant<int, char> &v);
+void cannotChangePtr(const std::variant<int, char> *v);
+
+char getUnknownChar();
+
+void swap(std::variant<int, char> &v1, std::variant<int, char> &v2) {
+  std::variant<int, char> tmp = v1;
+  v1 = v2;
+  v2 = tmp;
+}
+
+void cantDo(const std::variant<int, char>& v) {
+  std::variant<int, char> vtmp = v;
+  vtmp = 5;
+  int a = std::get<int> (vtmp);
+  (void*) a;
+}
+
+void changeVariantPtr(std::variant<int, char> *v) {
+  *v = 'c';
+}
+
+using var_t = std::variant<int, char>;
+using var_tt = var_t;
+using int_t = int;
+using char_t = char;
+
+
+//----------------------------------------------------------------------------//
+// std::get
+//----------------------------------------------------------------------------//
+void stdGetType() {
+  std::variant<int, char> v = 25;
+  int a = std::get<int>(v);
+  char c = std::get<char>(v); // expected-warning {{std::variant 'v' held an 'int' not a 'char'}}
+  (void*)a;
+  (void*)c;
+}
+
+void stdGetPointer() {
+  int *p = new int;
+  std::variant<int*, char> v = p;
+  int *a = std::get<int*>(v);
+  char c = std::get<char>(v); // expected-warning {{std::variant 'v' held an 'int *' not a 'char'}}
+  (void**)a;
+  (void*)c;
+  delete p;
+}
+
+void stdGetObject() {
+  std::variant<int, char, Foo> v = Foo{};
+  Foo f = std::get<Foo>(v);
+  int i = std::get<int>(v); // expected-warning {{std::variant 'v' held a 'Foo' not an 'int'}}
+  (void*)i;
+}
+
+void stdGetPointerAndPointee() {
+  int a = 5;
+  std::variant<int, int*> v = &a;
+  int *b = std::get<int*>(v);
+  int c = std::get<int>(v); // expected-warning {{std::variant 'v' held an 'int *' not an 'int'}}
+  (void*)c;
+  (void**)b;
+}
+
+void variantHoldingVariant() {
+  std::variant<std::variant<int, char>, std::variant<char, int>> v = std::variant<int,char>(25);
+  std::variant<int, char> v1 = std::get<std::variant<int,char>>(v);
+  std::variant<char, int> v2 = std::get<std::variant<char,int>>(v); // expected-warning {{std::variant 'v' held a 'std::variant<int, char>' not a 'class std::variant<char, int>'}}
+}
----------------
DonatNagyE wrote:

Beautiful testcase :1st_place_medal: 

Demonstrates the full glory of the type system...

https://github.com/llvm/llvm-project/pull/66481