Errors in transforming `struct T {} var`

[Ukilele]

Hey Andreas, I am sorry that I report so many issues recently, but cppinsights is just a great tool for learning C++ and it seems I occasionally tend to dig into the slightly more odd edge cases of the language 😸

Here is the source code:

struct A {
  void f() {}
} a_var_1;

struct B {
} b_var_1, b_var_2, b_var_3;

struct {
} anonym_var_1, anonym_var_2, anonym_var_3;

struct {
} anonym_var_assign = {};

struct {
} anonym_var_array[3];

struct {
} anonym_var_dummy, *anonym_var_ptr;

And this is what cppinsights (version 26c63ad828c5404233d8a080148e8cccb3b64f80) produces:

struct A a_var_1;


struct B b_var_3;


struct __anon_8_1
{
  // inline constexpr __anon_8_1() noexcept = default;
};

__anon_8_1 anonym_var_1;
, anonym_var_2__anon_8_1 anonym_var_2;
, anonym_var_3;__anon_8_1 anonym_var_3;


struct __anon_11_1
{
};

 = {};__anon_11_1 anonym_var_assign = {};


__anon_14_1 anonym_var_array[3];


__anon_17_1 * anonym_var_ptr;

I think there are several issues, but I assume they are related. So I hope it's fine that I create just one issue.

• [ ] 1. Creating a type and variable via struct A{} a_var_1; produces struct A a_var_1;. But instead it should show the whole type definition and a variable definition afterwards:

struct A {
  //...
};
A a_var_1;

• [ ] 2. Creating a type and multiple variables via struct B {} b_var_1, b_var_2, b_var_3; produces struct B b_var_3; (similar like in bullet point 1.). The additional issue is, that cppinsights completely swallows the definitions of b_var_1 and b_var_2.
• [ ] 3. Creating an anonymous type and multiple variables via struct {} anonym_var_1, anonym_var_2, anonym_var_3; does not swallow the first and second variables (other than in bullet point 2.), but only the definition of anonym_var_1 looks reasonable. The definitions of anonym_var_2 and anonym_var_3 look wrong.
• [ ] 4. Creating an anonymous type and one variable which gets initialized like in struct {} anonym_var_assign = {}; looks wrong in a sense that the initialization part ( = {};) appears both before and after the variable anonym_var_assign.
• [ ] 5. Creating an anonymous type and one or multiple variables with additional declarators (like array ([3]) or pointer (*)) leads to the effect that both the anonymous struct definition does not get generated by cppinsights and that previous variable definitions (anonym_var_dummy) get swallowed.

[andreasfertig]

Hello @Ukilele,

no worries, you help to improve C++ Insights, thank you for that :-).

As far as I could see, all the issues you report have one common root. When more than one variable is declared per line, or a type is defined in the same line, the AST matchers I use from Clang trigger on that line multiple times. What you then see is only the last rewrite that survives. A related issue (#500) reports the root of the trouble: int a,b,c also fails. Same reason. I don't know how to fix this with the current implementation of C++ Insights.

However, a way to fix this is to eliminate all the matches and traverse the TU. I have plans for that because this approach would also drop pounds of code I must maintain. The problem with the TU traverser is that I have to deal with includes that are not part of the AST. I can get them, but positioning them is an issue. By coincidence, I started looking at the TU approach this week. But I'm not sure whether I will make progress soon.

One easy fix to see the transformation is to wrap your code in a namespace. That way, the namespace matcher picks it up and rewrites it correctly.

Andreas

[Ukilele]

Thanks for your quick response :) And thanks for sharing the insights of cppinsights (pun intended). The namespace-workaround sounds good 👍