[clang] [clang-format] Add BreakBeforeTemplateClose option (PR #118046)

[Owen Pan via cfe-commits]

================
@@ -11220,6 +11220,333 @@ TEST_F(FormatTest, WrapsTemplateDeclarationsWithComments) {
       Style);
 }
 
+TEST_F(FormatTest, BreakBeforeTemplateCloser) {
+  FormatStyle Style = getGoogleStyle(FormatStyle::LK_Cpp);
+  // Begin with tests covering the case where there is no constraint on the
+  // column limit.
+  Style.ColumnLimit = 0;
+  // When BreakBeforeTemplateCloser is turned off, the line break that it adds
+  // shall be removed:
+  verifyFormat("template <\n"
+               "    typename Foo,\n"
+               "    typename Bar>\n"
+               "void foo() {}",
+               "template <\n"
+               "    typename Foo,\n"
+               "    typename Bar\n"
+               ">\n"
+               "void foo() {}",
+               Style);
+
+  Style.BreakBeforeTemplateCloser = FormatStyle::BBTCS_BlockIndent;
+  // BreakBeforeTemplateCloser should NOT force template declarations onto
+  // multiple lines.
+  verifyFormat("template <typename Foo>\n"
+               "void foo() {}",
+               Style);
+  verifyFormat("template <typename Foo, typename Bar>\n"
+               "void foo() {}",
+               Style);
+  // It should allow a line break, even when the typename is short.
+  // verifyNoChange is needed because the default behavior is one line.
+  verifyNoChange("template <\n"
+                 "    typename Foo\n"
+                 ">\n"
+                 "void foo() {}",
+                 Style);
+  verifyNoChange("template <\n"
+                 "    typename Foo,\n"
+                 "    typename Bar\n"
+                 ">\n"
+                 "void foo() {}",
+                 Style);
+  verifyNoChange("template <typename Foo,\n"
+                 "          typename Bar>\n"
+                 "void foo() {}",
+                 Style);
+  // It should add a line break before > if not already present:
+  verifyFormat("template <\n"
+               "    typename Foo\n"
+               ">\n"
+               "void foo() {}",
+               "template <\n"
+               "    typename Foo>\n"
+               "void foo() {}",
+               Style);
+  verifyFormat("template <\n"
+               "    typename Foo,\n"
+               "    typename Bar\n"
+               ">\n"
+               "void foo() {}",
+               "template <\n"
+               "    typename Foo,\n"
+               "    typename Bar>\n"
+               "void foo() {}",
+               Style);
+  // When within an indent scope, the > should be placed accordingly:
+  verifyFormat("struct Baz {\n"
+               "  template <\n"
+               "      typename Foo,\n"
+               "      typename Bar\n"
+               "  >\n"
+               "  void foo() {}\n"
+               "};",
+               "struct Baz {\n"
+               "  template <\n"
+               "      typename Foo,\n"
+               "      typename Bar>\n"
+               "  void foo() {}\n"
+               "};",
+               Style);
+
+  // Test from issue #80049:
+  verifyFormat(
+      "void foo() {\n"
+      "  using type = std::remove_cv_t<\n"
+      "      add_common_cv_reference<\n"
+      "          std::common_type_t<std::decay_t<T0>, std::decay_t<T1>>,\n"
+      "          T0,\n"
+      "          T1\n"
+      "      >\n"
+      "  >;\n"
+      "}",
+      "void foo() {\n"
+      "  using type = std::remove_cv_t<\n"
+      "      add_common_cv_reference<\n"
+      "          std::common_type_t<std::decay_t<T0>, std::decay_t<T1>>,\n"
+      "          T0,\n"
+      "          T1>>;\n"
+      "}",
+      Style);
+
+  // Test lambda goes to next line:
+  verifyFormat("void foo() {\n"
+               "  auto lambda = []<\n"
+               "                    typename T\n"
+               "                >(T t) {\n"
+               "  };\n"
+               "}",
+               "void foo() {\n"
+               "  auto lambda = []<\n"
+               "  typename T>(T t){\n"
+               "  };\n"
+               "}",
+               Style);
+  // With no column limit, two parameters can go on the same line:
+  verifyFormat("void foo() {\n"
+               "  auto lambda = []<\n"
+               "                    typename T, typename Foo\n"
+               "                >(T t) {\n"
+               "  };\n"
+               "}",
+               "void foo() {\n"
+               "  auto lambda = []<\n"
+               "  typename T, typename Foo>(T t){\n"
+               "  };\n"
+               "}",
+               Style);
+  // Or on different lines:
+  verifyFormat("void foo() {\n"
+               "  auto lambda = []<\n"
+               "                    typename T,\n"
+               "                    typename Foo\n"
+               "                >(T t) {\n"
+               "  };\n"
+               "}",
+               "void foo() {\n"
+               "  auto lambda = []<\n"
+               "  typename T,\n"
+               "  typename Foo>(T t){\n"
+               "  };\n"
+               "}",
+               Style);
+
+  // Note that this is the same line (no \n):
+  verifyFormat("void foo() {\n"
+               "  auto lambda = []<typename "
+               "Looooooooooooooooooooooooooooong>("
+               "Looooooooooooooooooooooooooooong t) {};\n"
+               "}",
+               Style);
+
+  // Test template usage goes to next line too:
+  verifyFormat("void foo() {\n"
+               "  myFunc<\n"
+               "      T\n"
+               "  >();\n"
+               "}",
+               "void foo() {\n"
+               "  myFunc<\n"
+               "  T>();\n"
+               "}",
+               Style);
+
+  // Now test that it handles the cases when the column limit forces wrapping.
+  Style.ColumnLimit = 40;
+  // When the column limit allows it, the template should be combined back into
+  // one line:
+  verifyFormat("template <typename Foo, typename Bar>\n"
+               "void foo() {}",
+               "template <\n"
+               "    typename Foo,\n"
+               "    typename Bar\n"
+               ">\n"
+               "void foo() {}",
+               Style);
+  // But not when the name is looong. Note that these names are exactly 1
+  // character too long for the ColumnLimit.
+  verifyFormat("template <\n"
+               "    typename Foo,\n"
+               "    typename Barrrrrrrrrrrrrrrrrrrr\n"
+               ">\n"
+               "void foo() {}",
+               Style);
----------------
owenca wrote:

Is this just 1 over `ColumnLimit`? Looks like we got a problem here:
```
$ cat a.cc
template <typename Barrrrrrrrrrrrrrrrrrr>
void foo() {}
$ clang-format -style='{ColumnLimit: 40, BreakBeforeTemplateCloser: BlockIndent}' a.cc
template <typename Barrrrrrrrrrrrrrrrrrr
>
void foo() {}
$ 
```
Shouldn't the output be the following instead?
```cpp
template <
    typename Barrrrrrrrrrrrrrrrrrr
>
void foo() {}
```
In comparison, both 19.1.7 and the default `Never` of this patch give the expected output below:
```
$ clang-format -style='{ColumnLimit: 40}' a.cc
template <
    typename Barrrrrrrrrrrrrrrrrrr>
void foo() {}
$ 
```

https://github.com/llvm/llvm-project/pull/118046