[PATCH] D148318: [clang-tidy] Add `performance-avoid-endl` check

[Nathan James via Phabricator via cfe-commits]

njames93 added a comment.

For what its worth, there typically isn't any performance gain using `\n` over `std::endl` when writing to `std::cerr` or `std::clog` (or their wide string counterparts) as every write operation on those implicitly calls flush.
However If the fix was changed to convert `std::cerr << "Hello" << std::endl` into `std::cerr << "Hello\n";` That would have a noticeable difference on performance(as it would only be 1 flush rather than 2).



================
Comment at: clang-tools-extra/clang-tidy/performance/AvoidEndlCheck.cpp:36
+
+  if (!EndlCall)
+    return;
----------------
Assert on this, all paths should have this node bound.


================
Comment at: clang-tools-extra/clang-tidy/performance/AvoidEndlCheck.cpp:40
+  auto Diag = diag(EndlCall->getBeginLoc(),
+                   "do not use std::endl with iostreams; use '\\n' instead");
+
----------------
Wrap the `std::endl` in single quotes.

Also it may be wise to spell this how the user has it spelt

```lang=c++
std::cout << std::endl; // do not use 'std::endl'
using namespace std;
cout << endl; // do not use 'endl'


================
Comment at: clang-tools-extra/test/clang-tidy/checkers/performance/avoid-endl.cpp:8-11
+    template <typename T>
+    basic_ostream& operator<<(T) {
+      return *this;
+    }
----------------
These definitions can be elided. Same goes below


================
Comment at: clang-tools-extra/test/clang-tidy/checkers/performance/avoid-endl.cpp:24-25
+
+  using ostream = basic_ostream<char>;
+  using iostream = basic_iostream<char>;
+
----------------
Can you also add definitions and tests for `std::wostream` with `std::wcout`/`std::wcerr`


================
Comment at: clang-tools-extra/test/clang-tidy/checkers/performance/avoid-endl.cpp:27-28
+
+  iostream cout;
+  iostream cerr;
+
----------------
`cout` and `cerr` aren't `iostreams`, they are just `ostreams`.


================
Comment at: clang-tools-extra/test/clang-tidy/checkers/performance/avoid-endl.cpp:46
+void bad() {
+  std::cout << "World" << std::endl;
+  // CHECK-MESSAGES: :[[@LINE-1]]:27: warning: do not use std::endl with iostreams; use '\n' instead
----------------
I know it's asking a lot, but it would be amazing if the fix here could be changed to
```lang=c++
std::cout << "World\n";```
To do this would require checking if the first argument to the `endl` `operator<<` call was another `operator<<` call whose second argument was a string literal.


================
Comment at: clang-tools-extra/test/clang-tidy/checkers/performance/avoid-endl.cpp:47
+  std::cout << "World" << std::endl;
+  // CHECK-MESSAGES: :[[@LINE-1]]:27: warning: do not use std::endl with iostreams; use '\n' instead
+  std::cerr << "World" << std::endl;
----------------
carlosgalvezp wrote:
> carlosgalvezp wrote:
> > Use CHECK-FIXES to also test the fixes.
> Please add the complete error message, which includes the check name in brackets (see similar tests as reference)
That's not necessary. A lot of test files elide this as there is nothing to gain from it.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D148318/new/

https://reviews.llvm.org/D148318