Fix FPs in lifetime checker

This fixes several FPs in the lifetime checker. It also fixes issue [8846](https://trac.cppcheck.net/ticket/8846):

```cpp
int * f(int a[])
{
        return a;
}
```

lib/astutils.cpp

@@ -76,6 +76,16 @@ bool astIsPointer(const Token *tok)
     return tok && tok->valueType() && tok->valueType()->pointer;
 }
 
+bool astIsIterator(const Token *tok)
+{
+    return tok && tok->valueType() && tok->valueType()->type == ValueType::Type::ITERATOR;
+}
+
+bool astIsContainer(const Token *tok)
+{
+    return tok && tok->valueType() && tok->valueType()->type == ValueType::Type::CONTAINER;
+}
+
 std::string astCanonicalType(const Token *expr)
 {
     if (!expr)

lib/astutils.h

@@ -45,6 +45,10 @@ bool astIsBool(const Token *tok);
 
 bool astIsPointer(const Token *tok);
 
+bool astIsIterator(const Token *tok);
+
+bool astIsContainer(const Token *tok);
+
 /**
  * Get canonical type of expression. const/static/etc are not included and neither *&.
  * For example:

lib/checkautovariables.cpp

@@ -579,6 +579,13 @@ static bool isDeadScope(const Token * tok, const Scope * scope)
     return false;
 }
 
+static int getPointerDepth(const Token *tok)
+{
+    if (!tok)
+        return 0;
+    return tok->valueType() ? tok->valueType()->pointer : 0;
+}
+
 void CheckAutoVariables::checkVarLifetimeScope(const Token * start, const Token * end)
 {
     if (!start)
@@ -597,7 +604,7 @@ void CheckAutoVariables::checkVarLifetimeScope(const Token * start, const Token
             if (val.tokvalue == tok)
                 continue;
             if (Token::Match(tok->astParent(), "return|throw")) {
-                if (isInScope(val.tokvalue, scope)) {
+                if (getPointerDepth(tok) >= getPointerDepth(val.tokvalue) && isInScope(val.tokvalue, scope)) {
                     errorReturnDanglingLifetime(tok, &val);
                     break;
                 }

lib/valueflow.cpp

@@ -431,9 +431,10 @@ static void setTokenValue(Token* tok, const ValueFlow::Value &value, const Setti
     }
 
     if (value.isLifetimeValue()) {
-        if (value.lifetimeKind == ValueFlow::Value::Iterator && parent->isArithmeticalOp()) {
+        if (value.lifetimeKind == ValueFlow::Value::Iterator && astIsIterator(parent)) {
             setTokenValue(parent,value,settings);
-        } else if (astIsPointer(tok) && astIsPointer(parent) && (parent->isArithmeticalOp() || Token::Match(parent, "( %type%"))) {
+        } else if (astIsPointer(tok) && astIsPointer(parent) &&
+                   (parent->isArithmeticalOp() || Token::Match(parent, "( %type%"))) {
             setTokenValue(parent,value,settings);
         }
         return;
@@ -2763,7 +2764,8 @@ static void valueFlowLifetime(TokenList *tokenlist, SymbolDatabase*, ErrorLogger
             const Variable * var = getLifetimeVariable(tok, errorPath);
             if (!var)
                 continue;
-            if (var->isArray() && tok->astParent() && (astIsPointer(tok->astParent()) || Token::Match(tok->astParent(), "%assign%|return"))) {
+            if (var->isArray() && !var->isArgument() && tok->astParent() &&
+                (astIsPointer(tok->astParent()) || Token::Match(tok->astParent(), "%assign%|return"))) {
                 errorPath.emplace_back(tok, "Array decayed to pointer here.");
 
                 ValueFlow::Value value;

test/testautovariables.cpp

@@ -1192,6 +1192,13 @@ private:
               "}");
 
         ASSERT_EQUALS("", errout.str());
+
+        check("int * foo(int * y)\n"
+              "{\n"
+              "  return y;\n"
+              "}");
+
+        ASSERT_EQUALS("", errout.str());
     }
 
     void testconstructor() { // Ticket #5478 - crash while checking a constructor
@@ -1359,6 +1366,27 @@ private:
               "}\n");
         ASSERT_EQUALS("", errout.str());
 
+        check("std::vector<int>::iterator f(std::vector<int>* v) {\n"
+              "    return v->begin();\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
+
+        check("std::vector<int>::iterator f(std::vector<int>* v) {\n"
+              "    std::vector<int>* v = new std::vector<int>();\n"
+              "    return v->begin();\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
+
+        check("int f(std::vector<int> v) {\n"
+              "    return *v.begin();\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
+
+        check("int f(std::vector<int> v) {\n"
+              "    return v.end() - v.begin();\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
+
         check("auto g() {\n"
               "    std::vector<char> v;\n"
               "    return {v, [v]() { return v.data(); }};\n"
@@ -1394,6 +1422,11 @@ private:
               "}\n");
         ASSERT_EQUALS("", errout.str());
 
+        check("int * f(int a[]) {\n"
+              "    return a;\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
+
         // Make sure we dont hang
         check("struct A;\n"
               "void f() {\n"