Provide better error message when assigning to tuple element

CHANGELOG.md

@@ -54,6 +54,8 @@ and this project adheres to
   - [#1542](https://github.com/iovisor/bpftrace/pull/1542)
 - Change a part of the message of '-v' output
   - [#1553](https://github.com/iovisor/bpftrace/pull/1553)
+- Improve tuple assignment error message
+  - [#1563](https://github.com/iovisor/bpftrace/pull/1563)
 
 #### Deprecated
 

src/parser.yy

@@ -265,6 +265,7 @@ stmt : expr                { $$ = new ast::ExprStatement($1); }
      | jump_stmt           { $$ = $1; }
      | map "=" expr        { $$ = new ast::AssignMapStatement($1, $3, @2); }
      | var "=" expr        { $$ = new ast::AssignVarStatement($1, $3, @2); }
+     | tuple_assignment
      ;
 
 compound_assignment : map LEFTASSIGN expr  { $$ = new ast::AssignMapStatement($1, new ast::Binop($1, token::LEFT,  $3, @2)); }
@@ -289,6 +290,8 @@ compound_assignment : map LEFTASSIGN expr  { $$ = new ast::AssignMapStatement($1
                     | var BXORASSIGN expr  { $$ = new ast::AssignVarStatement($1, new ast::Binop($1, token::BXOR,  $3, @2)); }
                     ;
 
+tuple_assignment : expr DOT INT "=" expr { error(@1 + @5, "Tuples are immutable once created. Consider creating a new tuple and assigning it instead."); YYERROR; }
+
 int : MINUS INT    { $$ = new ast::Integer(-1 * $2, @$); }
     | INT          { $$ = new ast::Integer($1, @$); }
     ;

tests/parser.cpp

@@ -1663,6 +1663,30 @@ TEST(Parser, while_loop)
 )PROG");
 }
 
+TEST(Parser, tuple_assignment_error_message)
+{
+  BPFtrace bpftrace;
+  std::stringstream out;
+  Driver driver(bpftrace, out);
+  EXPECT_EQ(driver.parse_str("i:s:1 { @x = (1, 2); $x.1 = 1; }"), 1);
+  std::string expected =
+      R"(stdin:1:22-30: ERROR: Tuples are immutable once created. Consider creating a new tuple and assigning it instead.
+i:s:1 { @x = (1, 2); $x.1 = 1; }
+                     ~~~~~~~~
+)";
+  EXPECT_EQ(out.str(), expected);
+}
+
+TEST(Parser, tuple_assignment_error)
+{
+  test_parse_failure("i:s:1 { (1, 0) = 0 }");
+  test_parse_failure("i:s:1 { ((1, 0), 3).0.0 = 3 }");
+  test_parse_failure("i:s:1 { ((1, 0), 3).0 = (0, 1) }");
+  test_parse_failure("i:s:1 { (1, \"two\", (3, 4)).5 = \"six\"; }");
+  test_parse_failure("i:s:1 { $a = 1; $a.2 = 3 }");
+  test_parse_failure("i:s:1 { 0.1 = 1.0 }");
+}
+
 } // namespace parser
 } // namespace test
 } // namespace bpftrace