Bug 20416 – [Regression 2.073.2] compiler complains about escaping reference in certain cases

In some cases, when a function returns the result of a ref function by value, the compiler complains that it's escaping a local reference. An example case: struct S { string x; } ref S foo(return ref S s) { return s; } S bar() { S result; return foo(result); } Error: returning foo(result) escapes a reference to local variable result Note the return attribute in foo is significant. Without that it succeeds. Also significant is that S contains a string. If you replace it with an int, it works. Probably has something to do with the indirection in the string. Clearly, we aren't returning by ref from bar, but the compiler fails to see this. Seems to be a regression for 2.073 (where dip1000 was introduced). With -dip1000 switch, it still fails. Workaround is to call foo, and then return result directly, which oddly shows no complaint even though it's equivalent.

A simpler test case: alias P = int*; ref P foo(return ref P); P bar() { P result; return foo(result); } dmd -c test -dip1000 test.d(12): Error: returning foo(result) escapes a reference to local variable result

@WalterBright updated dlang/dmd pull request #10640 "fix Issue 20416 - [Regression 2.073.2] compiler complains about escap…" fixing this issue: - fix Issue 20416 - [Regression 2.073.2] compiler complains about escaping reference in certain cases https://github.com/dlang/dmd/pull/10640

dlang/dmd pull request #10640 "fix Issue 20416 - [Regression 2.073.2] compiler complains about escap…" was merged into stable: - a1d82c6eec6d793e0334a71f63a22589a43d0cb0 by Walter Bright: fix Issue 20416 - [Regression 2.073.2] compiler complains about escaping reference in certain cases https://github.com/dlang/dmd/pull/10640