Restrict use some map aggregation types

lhist/hist/stats have some restrictions in that
they cannot be referenced inside tuples and single
key values cannot be printed; the entire map must
be printed. This latter restriction could be relaxed;
it just requires the development work to support it.

Issue: bpftrace#3540

Author: Jordan Rome

src/ast/passes/semantic_analyser.cpp

@@ -131,7 +131,7 @@ static bool IsValidVarDeclType(const SizedType &ty)
 // `@a = hist(10); @b = @a;`
 static bool IsValidAssignment(const SizedType &ty, bool is_map)
 {
-  if (is_map && (ty.IsHistTy() || ty.IsLhistTy() || ty.IsStatsTy())) {
+  if (is_map && (ty.IsMultiOutputMapTy())) {
     return false;
   }
   return true;
@@ -1209,10 +1209,16 @@ void SemanticAnalyser::visit(Call &call)
       if (arg.is_map) {
         Map &map = static_cast<Map &>(arg);
         if (map.key_expr) {
-          if (call.vargs.size() > 1)
+          if (call.vargs.size() > 1) {
             LOG(ERROR, call.loc, err_) << "Single-value (i.e. indexed) map "
                                           "print cannot take additional "
                                           "arguments.";
+          } else if (map.type.IsMultiOutputMapTy()) {
+            LOG(ERROR, call.loc, err_)
+                << "Map type " << map.type
+                << " cannot print the value of individual keys. You must print "
+                   "the whole map.";
+          }
         }
 
         if (is_final_pass()) {
@@ -2756,8 +2762,12 @@ void SemanticAnalyser::visit(Tuple &tuple)
     // If elem type is none that means that the tuple contains some
     // invalid cast (e.g., (0, (aaa)0)). In this case, skip the tuple
     // creation. Cast already emits the error.
-    if (elem->type.IsNoneTy() || elem->type.GetSize() == 0)
+    if (elem->type.IsNoneTy() || elem->type.GetSize() == 0) {
       return;
+    } else if (elem->type.IsMultiOutputMapTy()) {
+      LOG(ERROR, elem->loc, err_)
+          << "Map type " << elem->type << " cannot exist inside a tuple.";
+    }
     elements.emplace_back(elem->type);
   }
 

src/types.h

@@ -478,8 +478,15 @@ class SizedType {
   }
   bool IsMapIterableTy() const
   {
-    return !(type_ == Type::hist_t || type_ == Type::lhist_t ||
-             type_ == Type::stats_t);
+    return !IsMultiOutputMapTy();
+  }
+
+  // These are special map value types that can't be reduced to a single value
+  // and output multiple lines when printed
+  bool IsMultiOutputMapTy() const
+  {
+    return type_ == Type::hist_t || type_ == Type::lhist_t ||
+           type_ == Type::stats_t;
   }
 
   bool NeedsPercpuMap() const;

tests/semantic_analyser.cpp

@@ -1041,6 +1041,11 @@ BEGIN { print(@x[2]); }
 stdin:1:20-38: ERROR: Single-value (i.e. indexed) map print cannot take additional arguments.
 BEGIN { @x[1] = 1; print(@x[1], 3, 5); }
                    ~~~~~~~~~~~~~~~~~~
+)");
+  test_error("BEGIN { @x[1] = hist(10); print(@x[1]); }", R"(
+stdin:1:27-39: ERROR: Map type hist_t cannot print the value of individual keys. You must print the whole map.
+BEGIN { @x[1] = hist(10); print(@x[1]); }
+                          ~~~~~~~~~~~~
 )");
 }
 
@@ -3428,6 +3433,12 @@ BEGIN { $t = ((uint8)1, (2, 3)); $t = (4, ((int8)5, 6)); }
 
   test(R"_(BEGIN { @t = (1, 2, "hi"); @t = (3, 4, "hellolongstr"); })_");
   test(R"_(BEGIN { $t = (1, ("hi", 2)); $t = (3, ("hellolongstr", 4)); })_");
+
+  test_error("BEGIN { @x[1] = hist(10); $y = (1, @x[1]); }", R"(
+stdin:1:36-41: ERROR: Map type hist_t cannot exist inside a tuple.
+BEGIN { @x[1] = hist(10); $y = (1, @x[1]); }
+                                   ~~~~~
+)");
 }
 
 TEST(semantic_analyser, tuple_indexing)