[clang] [clang-tools-extra] [clang-tidy] Add readability-avoid-default-lambda-capture (PR #160150)

[Baranov Victor via cfe-commits]

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@@ -0,0 +1,143 @@
+// RUN: %check_clang_tidy %s readability-avoid-default-lambda-capture %t -- -- -Wno-vla-extension
+
+void test_default_captures() {
+  int value = 42;
+  int another = 10;
+
+  auto lambda1 = [=](int x) { return value + x; };
+  // CHECK-MESSAGES: :[[@LINE-1]]:19: warning: lambda default captures are discouraged; prefer to capture specific variables explicitly [readability-avoid-default-lambda-capture]
+  // CHECK-FIXES: auto lambda1 = [value](int x) { return value + x; };
+
+  auto lambda2 = [&](int x) { return value + x; };
+  // CHECK-MESSAGES: :[[@LINE-1]]:19: warning: lambda default captures are discouraged; prefer to capture specific variables explicitly [readability-avoid-default-lambda-capture]
+  // CHECK-FIXES: auto lambda2 = [&value](int x) { return value + x; };
+
+  auto lambda3 = [=, &another](int x) { return value + another + x; };
+  // CHECK-MESSAGES: :[[@LINE-1]]:19: warning: lambda default captures are discouraged; prefer to capture specific variables explicitly [readability-avoid-default-lambda-capture]
+  // CHECK-FIXES: auto lambda3 = [value, &another](int x) { return value + another + x; };
+
+  auto lambda4 = [&, value](int x) { return value + another + x; };
+  // CHECK-MESSAGES: :[[@LINE-1]]:19: warning: lambda default captures are discouraged; prefer to capture specific variables explicitly [readability-avoid-default-lambda-capture]
+  // CHECK-FIXES: auto lambda4 = [&another, value](int x) { return value + another + x; };
+}
+
+void test_acceptable_captures() {
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vbvictor wrote:

Please add more tests with different capture syntax from
https://en.cppreference.com/w/cpp/language/lambda.html:
```
The syntax of capture is defined as follows:

identifier	(1)	
identifier ...	(2)	
identifier initializer	(3)	(since C++14)
& identifier	(4)	
& identifier ...	(5)	
& identifier initializer	(6)	(since C++14)
this	(7)	
* this	(8)	(since C++17)
... identifier initializer	(9)	(since C++20)
& ... identifier initializer	(10)	(since C++20)
```

So it could be a pack expansion lambda (I've never seen any). If it couldn't be captured by `&` or `=`, make test that it is correctly rewrote when `=` is present.


https://github.com/llvm/llvm-project/pull/160150