[clang] clang-format: Add "AllowShortNamespacesOnASingleLine" option (PR #105597)

[Galen Elias via cfe-commits]

================
@@ -27981,6 +27981,132 @@ TEST_F(FormatTest, BreakBinaryOperations) {
                Style);
 }
 
+TEST_F(FormatTest, ShortNamespacesOption) {
+  auto BaseStyle = getLLVMStyle();
+  BaseStyle.AllowShortNamespacesOnASingleLine = true;
+  BaseStyle.FixNamespaceComments = false;
+
+  auto Style = BaseStyle;
+
+  // Basic functionality.
+  verifyFormat("namespace foo { class bar; }", Style);
+  verifyFormat("namespace foo::bar { class baz; }", Style);
+  verifyFormat("namespace { class bar; }", Style);
+  verifyFormat("namespace foo {\n"
+               "class bar;\n"
+               "class baz;\n"
+               "}",
+               Style);
+
+  // Trailing comments prevent merging.
+  verifyFormat("namespace foo {\n"
+               "namespace baz { class qux; } // comment\n"
+               "}",
+               Style);
+
+  // Make sure code doesn't walk too far on unbalanced code.
+  verifyFormat("namespace foo {", Style);
+  verifyFormat("namespace foo {\n"
+               "class baz;",
+               Style);
+  verifyFormat("namespace foo {\n"
+               "namespace bar { class baz; }",
+               Style);
+
+  // Nested namespaces.
+  verifyFormat("namespace foo { namespace bar { class baz; } }", Style);
+  verifyFormat("namespace foo {\n"
+               "namespace bar { class baz; }\n"
+               "namespace qux { class quux; }\n"
+               "}",
+               Style);
+
+  // Varying inner content.
+  verifyFormat("namespace foo {\n"
+               "int f() { return 5; }\n"
+               "}",
+               Style);
+  verifyFormat("namespace foo { template <T> struct bar; }", Style);
+  verifyFormat("namespace foo { constexpr int num = 42; }", Style);
+
+  // Validate wrapping scenarios around the ColumnLimit.
+  Style.ColumnLimit = 64;
+
+  // Validate just under the ColumnLimit.
+  verifyFormat(
+      "namespace foo { namespace bar { namespace baz { class qux; } } }",
+      Style);
+
+  // Validate just over the ColumnLimit.
+  verifyFormat("namespace foo {\n"
+               "namespace bar { namespace baz { class quux; } }\n"
+               "}",
+               Style);
+
+  verifyFormat("namespace foo {\n"
+               "namespace bar {\n"
+               "namespace baz { namespace qux { class quux; } }\n"
+               "}\n"
+               "}",
+               Style);
+
+  // Validate that the ColumnLimit logic accounts for trailing content as well.
+  verifyFormat("namespace foo {\n"
+               "namespace bar { namespace baz { class qux; } }\n"
+               "} // extra",
+               Style);
+
+  // No ColumnLimit, allows long nested one-liners, but also leaves multi-line
+  // instances alone.
+  Style.ColumnLimit = 0;
+  verifyFormat(
+      "namespace foo { namespace bar { namespace baz { class qux; } } }",
+      Style);
+
+  verifyNoChange("namespace foo {\n"
+                 "namespace bar { namespace baz { class qux; } }\n"
+                 "}",
+                 Style);
----------------
galenelias wrote:

Well, you would probably be more the expert on the intended design of 'ColumnLimit: 0', but my mental model of ColumnLimit: 0 is basically that it will respect the line breaks in the existing code as long as they fall on valid 'seams'.  This lets you make really long lines, but also lets you produce very short lines by the same token, because it's basically taking the existing wrapping as the truth, assuming it's a valid wrapping.  I personally really value this behavior in the code-base I work on, so I wouldn't consider these instances a bug (same goes for the linked discourse link).

https://github.com/llvm/llvm-project/pull/105597