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Merge pull request #34 from plasma-umass/template-recursion-example
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Add infinite template recursion example
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@emeryberger
emeryberger committed Oct 1, 2023
2 parents 0b4ce60 + 052fd2a commit 6b69a11
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87 changes: 87 additions & 0 deletions tests/.regression/macos/clang++/template-recursion.cpp
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===================== Prompt =====================
This is my code:

File `/Applications/Xcode_14.2.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/span`:
```
418 enable_if_t<is_convertible_v<const _OtherElementType(*)[], element_type (*)[]>, nullptr_t> = nullptr>
419 _LIBCPP_INLINE_VISIBILITY
420 constexpr span(const array<_OtherElementType, _Sz>& __arr) noexcept : __data{__arr.data()}, __size{_Sz} {}
421
422 template <class _Container>
423 _LIBCPP_INLINE_VISIBILITY
424 constexpr span( _Container& __c,
425 enable_if_t<__is_span_compatible_container<_Container, _Tp>::value, nullptr_t> = nullptr)
426 : __data{_VSTD::data(__c)}, __size{(size_type) _VSTD::size(__c)} {}
427
428 template <class _Container>
```

File `/Users/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp`:
```
4 #include <iterator>
5 #include <numeric>
6 #include <span>
7 #include <vector>
8
9 template <std::uint32_t M, std::uint32_t N>
10 struct Matrix {
11 Matrix(std::span<std::uint64_t> underlying) : underlying(underlying) {
12 assert(underlying.size() == M * N);
13 }
14
15 std::uint64_t lowestRowSum() const {
16 const auto firstRowSum
17 = std::accumulate(underlying.begin(), std::next(underlying.begin(), N), std::uint64_t(0));
18 const auto subMatrix = Matrix<M - 1, N>(underlying.subspan(N));
19 return std::min(firstRowSum, subMatrix.lowestRowSum());
20 }
21
22 private:
```

File `/Users/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp`:
```
30 int main() {
31 std::vector<std::uint64_t> v(M * N);
32 for (int i = 0; i < M * N; ++i) {
33 v[i] = i;
34 }
35 const auto lowestRowSum = Matrix<M, N>(v).lowestRowSum();
36 }
```


This is my error:
```
In file included from /Users/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:6:
/Applications/Xcode_14.2.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/span:425:71: fatal error: recursive template instantiation exceeded maximum depth of 1024
enable_if_t<__is_span_compatible_container<_Container, _Tp>::value, nullptr_t> = nullptr)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
/Users/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:11:51: note: while substituting deduced template arguments into function template 'span' [with _Container = std::span<unsigned long long, 18446744073709551615>]
Matrix(std::span<std::uint64_t> underlying) : underlying(underlying) {
^
/Users/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:18:32: note: in instantiation of member function 'Matrix<4294966373, 10>::Matrix' requested here
const auto subMatrix = Matrix<M - 1, N>(underlying.subspan(N));
^
/Users/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:19:48: note: in instantiation of member function 'Matrix<4294966374, 10>::lowestRowSum' requested here
return std::min(firstRowSum, subMatrix.lowestRowSum());

[...]

^
/Users/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:19:48: note: in instantiation of member function 'Matrix<4294966375, 10>::lowestRowSum' requested here
/Users/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:19:48: note: in instantiation of member function 'Matrix<4294966376, 10>::lowestRowSum' requested here
/Users/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:19:48: note: (skipping 1015 contexts in backtrace; use -ftemplate-backtrace-limit=0 to see all)
/Users/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:19:48: note: in instantiation of member function 'Matrix<96, 10>::lowestRowSum' requested here
/Users/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:19:48: note: in instantiation of member function 'Matrix<97, 10>::lowestRowSum' requested here
/Users/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:19:48: note: in instantiation of member function 'Matrix<98, 10>::lowestRowSum' requested here
/Users/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:19:48: note: in instantiation of member function 'Matrix<99, 10>::lowestRowSum' requested here
/Users/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:35:47: note: in instantiation of member function 'Matrix<100, 10>::lowestRowSum' requested here
const auto lowestRowSum = Matrix<M, N>(v).lowestRowSum();
^
1 error generated.
```


What's the problem?
==================================================
49 changes: 49 additions & 0 deletions tests/.regression/ubuntu/clang++-17/template-recursion.cpp
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===================== Prompt =====================
This is my code:

File `/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp`:
```
4 #include <iterator>
5 #include <numeric>
6 #include <span>
7 #include <vector>
8
9 template <std::uint32_t M, std::uint32_t N>
10 struct Matrix {
11 Matrix(std::span<std::uint64_t> underlying) : underlying(underlying) {
12 assert(underlying.size() == M * N);
13 }
```

File `/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp`:
```
18 const auto subMatrix = Matrix<M - 1, N>(underlying.subspan(N));
19 return std::min(firstRowSum, subMatrix.lowestRowSum());
20 }
21
22 private:
23 // The Matrix object does not own the underlying memory, and is just used to perform operations.
24 std::span<std::uint64_t> underlying;
25 };
26
27 #define M 100
```


This is my error:
```
/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:11:17: error: no template named 'span' in namespace 'std'
11 | Matrix(std::span<std::uint64_t> underlying) : underlying(underlying) {
| ~~~~~^
/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:24:10: error: no template named 'span' in namespace 'std'

[...]

24 | std::span<std::uint64_t> underlying;
| ~~~~~^
2 errors generated.
```


What's the problem?
==================================================
75 changes: 75 additions & 0 deletions tests/.regression/ubuntu/g++-12/template-recursion.cpp
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===================== Prompt =====================
This is my code:

File `/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp`:
```
3 #include <cstddef>
4 #include <iterator>
5 #include <numeric>
6 #include <span>
7 #include <vector>
8
9 template <std::uint32_t M, std::uint32_t N>
10 struct Matrix {
11 Matrix(std::span<std::uint64_t> underlying) : underlying(underlying) {
12 assert(underlying.size() == M * N);
13 }
14
15 std::uint64_t lowestRowSum() const {
16 const auto firstRowSum
17 = std::accumulate(underlying.begin(), std::next(underlying.begin(), N), std::uint64_t(0));
18 const auto subMatrix = Matrix<M - 1, N>(underlying.subspan(N));
19 return std::min(firstRowSum, subMatrix.lowestRowSum());
20 }
21
22 private:
23 // The Matrix object does not own the underlying memory, and is just used to perform operations.
24 std::span<std::uint64_t> underlying;
25 };
26
27 #define M 100
28 #define N 10
29
30 int main() {
31 std::vector<std::uint64_t> v(M * N);
32 for (int i = 0; i < M * N; ++i) {
33 v[i] = i;
34 }
35 const auto lowestRowSum = Matrix<M, N>(v).lowestRowSum();
36 }
```


This is my error:
```
/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:11:21: error: expected ‘)’ before ‘<’ token
11 | Matrix(std::span<std::uint64_t> underlying) : underlying(underlying) {
| ~ ^
| )
/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:24:10: error: ‘span’ in namespace ‘std’ does not name a template type
24 | std::span<std::uint64_t> underlying;
| ^~~~
/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp: In member function ‘uint64_t Matrix<M, N>::lowestRowSum() const’:
/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:17:31: error: ‘underlying’ was not declared in this scope
17 | = std::accumulate(underlying.begin(), std::next(underlying.begin(), N), std::uint64_t(0));
| ^~~~~~~~~~
/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp: In function ‘int main()’:

[...]

/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:35:45: error: no matching function for call to ‘Matrix<100, 10>::Matrix(std::vector<long unsigned int>&)’
35 | const auto lowestRowSum = Matrix<M, N>(v).lowestRowSum();
| ^
/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:10:8: note: candidate: ‘constexpr Matrix<100, 10>::Matrix()’
10 | struct Matrix {
| ^~~~~~
/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:10:8: note: candidate expects 0 arguments, 1 provided
/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:10:8: note: candidate: ‘constexpr Matrix<100, 10>::Matrix(const Matrix<100, 10>&)’
/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:10:8: note: no known conversion for argument 1 from ‘std::vector<long unsigned int>’ to ‘const Matrix<100, 10>&’
/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:10:8: note: candidate: ‘constexpr Matrix<100, 10>::Matrix(Matrix<100, 10>&&)’
/home/runner/work/cwhy/cwhy/tests/c++/template-recursion.cpp:10:8: note: no known conversion for argument 1 from ‘std::vector<long unsigned int>’ to ‘Matrix<100, 10>&&’
```


What's the problem?
==================================================
36 changes: 36 additions & 0 deletions tests/c++/template-recursion.cpp
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#include <algorithm>
#include <cassert>
#include <cstddef>
#include <iterator>
#include <numeric>
#include <span>
#include <vector>

template <std::uint32_t M, std::uint32_t N>
struct Matrix {
Matrix(std::span<std::uint64_t> underlying) : underlying(underlying) {
assert(underlying.size() == M * N);
}

std::uint64_t lowestRowSum() const {
const auto firstRowSum
= std::accumulate(underlying.begin(), std::next(underlying.begin(), N), std::uint64_t(0));
const auto subMatrix = Matrix<M - 1, N>(underlying.subspan(N));
return std::min(firstRowSum, subMatrix.lowestRowSum());
}

private:
// The Matrix object does not own the underlying memory, and is just used to perform operations.
std::span<std::uint64_t> underlying;
};

#define M 100
#define N 10

int main() {
std::vector<std::uint64_t> v(M * N);
for (int i = 0; i < M * N; ++i) {
v[i] = i;
}
const auto lowestRowSum = Matrix<M, N>(v).lowestRowSum();
}

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