Bug 23300 – std.array : array wrongly propagates scopeness of source

This should compile but does not on dmd 2.100, using -preview=dip1000 flag. ------------- @safe int[] fun() { import std : array, map; scope r = [1,2,3].map!"a+3"; return r.array; } ------------- Were I returning `r` directly, this would be escaping a reference to scoped data, but `array` copies the data. Returning `array`ed range should be allowed, `scope` or no.

(In reply to Ate Eskola from comment #0) > This should compile but does not on dmd 2.100, using -preview=dip1000 flag. > > ------------- > @safe int[] fun() > { import std : array, map; > scope r = [1,2,3].map!"a+3"; > return r.array; > } > ------------- > > Were I returning `r` directly, this would be escaping a reference to scoped > data, but `array` copies the data. Returning `array`ed range should be > allowed, `scope` or no. The problem here is that `r` is `scope` so for it to be able to be passed to `array`, `array` also needs to receive a scope parameter. However, `array`'s parameter cannot be `scope` because it is copied into allocated memory. By the current scope rules this seems to be correct behavior, making this bug report invalid.

(In reply to RazvanN from comment #1) > However, `array`'s > parameter cannot be `scope` because it is copied into allocated memory. The parameter to `array` should infer `scope` unless the range has non-scope range primitives. It's not escaping the input array, it's dereferencing it and copying the elements into a new GC array which is not scope. `scope` inference fails and it falls back on `return scope` inference from `pure`. By making it impure, the newest DMD reports: test_.d(12): Error: scope variable `r` assigned to non-scope parameter `r` calling `array` std/array.d(112): which is not `scope` because of `__r353 = r` https://github.com/dlang/phobos/blob/b578dfad94770574d7e522557a77276c35943daa/std/array.d#L112 So the underlying problem is that `scope` inference is defeated by `foreach` on a struct with range primitives.

I narrowed down what causes the inference to fail ------ auto fun(int* ptr) { // comment out this line and this compiles // as does if you explicitly mark either it or the argument scope auto r = ptr; return new int; } @safe int* gun(scope int* ptr){return ptr.fun;} ------ Is the scope inference supposed to behave like this?

(In reply to Ate Eskola from comment #3) > ------ > auto fun(int* ptr) > { // comment out this line and this compiles > // as does if you explicitly mark either it or the argument scope > auto r = ptr; > return new int; > } > > @safe int* gun(scope int* ptr){return ptr.fun;} > ------ > > Is the scope inference supposed to behave like this? That's issue 20674 ("[DIP1000] inference of `scope` is easily confused").

Thanks. The current attitude of Walter seems to be that yes, the inference is working as it should. I do aknowledge that this isn't necessarily set in stone - we might still reach consensus to change the language. But as long as the status quo stays what it is now, this is a Phobos bug. `array` should be changed so that it compiles my first example with the current language rules.

*** Issue 23657 has been marked as a duplicate of this issue. ***

@dkorpel updated dlang/dmd pull request #14492 "Fix 20674, 23208, 23300 - improve `scope` inference" fixing this issue: - Fix 20674, 23208, 23300, 23294 - improve `scope` inference https://github.com/dlang/dmd/pull/14492

Note that this bug does not require DIP1000, and breaks compilation since 2.101. https://issues.dlang.org/show_bug.cgi?id=23657

@dkorpel created dlang/dmd pull request #16724 "Fix bugzilla 23300 - std.array : array wrongly propagates scopeness o…" fixing this issue: - Fix bugzilla 23300 - std.array : array wrongly propagates scopeness of source https://github.com/dlang/dmd/pull/16724

@dkorpel created dlang/phobos pull request #9026 "Bugzilla 23300 - add testcase for std.array on scope InputRange" mentioning this issue: - Bugzilla 23300 - add testcase for std.array on scope InputRange https://github.com/dlang/phobos/pull/9026

dlang/dmd pull request #16724 "Fix bugzilla 23300 - std.array : array wrongly propagates scopeness o…" was merged into master: - 6a041f8fc712bffd3a35326be99650ac28361477 by Dennis Korpel: Fix bugzilla 23300 - std.array : array wrongly propagates scopeness of source https://github.com/dlang/dmd/pull/16724

dlang/phobos pull request #9026 "Bugzilla 23300 - add testcase for std.array on scope InputRange" was merged into master: - 2959a226413076670120a76631aa85cc5f1291c6 by Dennis Korpel: Bugzilla 23300 - add testcase for std.array on scope InputRange https://github.com/dlang/phobos/pull/9026