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Build fails with recent master branch of Emacs #405

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yasuhirokimura opened this issue Jun 17, 2023 · 3 comments
Closed

Build fails with recent master branch of Emacs #405

yasuhirokimura opened this issue Jun 17, 2023 · 3 comments
Labels
bug Existing behavior is incorrect
Projects
Release 2.20.0
Milestone
2.20.0

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@yasuhirokimura
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After 96eaba0 is committed, Build fails with recent master branch of Emacs as following.

yasu@rolling[1016]% make
emacs -Q -batch -L . -eval '(setq byte-compile-error-on-warn t)' -f batch-byte-compile dash.el
emacs -Q -batch -L . -eval '(setq byte-compile-error-on-warn t)' -f batch-byte-compile dev/dash-defs.el
emacs -Q -batch -L . -eval '(setq byte-compile-error-on-warn t)' -f batch-byte-compile dev/examples.el

In toplevel form:
dev/examples.el: Error: `setcar' on constant list (arg 1)
make: *** [Makefile:69: dev/examples.elc] Error 1
yasu@rolling[1017]%

The failure doesn't happen with Emacs 28.2
@basil-conto
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Thank you for reporting this.
I noticed this as well, but while fixing it noticed what I thought was a bug in Emacs, then ran out of time. I'll have a look again now.

@basil-conto
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while fixing it noticed what I thought was a bug in Emacs

Now reported as https://bugs.gnu.org/64127.

@basil-conto basil-conto added the upstream Issue lies with Emacs itself label Jun 17, 2023
basil-conto added a commit that referenced this issue Jun 17, 2023
@basil-conto
No longer mark some functions are pure
fec9370 
Functions that guarantee a fresh return value should not be pure,
since their return value is likely to be mutated destructively:
https://bugs.gnu.org/64127

* NEWS.md (2.20.0): List affected functions.
* dash.el (-non-nil, -cons*, -snoc, -slice, -take, -take-last)
(-drop-last, -split-at, -interpose, -interleave, -repeat, -iota)
(-clone): No longer mark as pure.
* dev/examples.el (-powerset): Avoid mutating constant.

Fixes #405.
@basil-conto
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while fixing it noticed what I thought was a bug in Emacs

Now reported as https://bugs.gnu.org/64127.

Turns out it was my misunderstanding of what marking a function as pure implies: since pure function calls with constant arguments are evaluated at compile time, it is no longer safe to mutate their return value in the general case.

@basil-conto basil-conto added bug Existing behavior is incorrect and removed upstream Issue lies with Emacs itself labels Jun 17, 2023
@basil-conto basil-conto added this to the 2.20.0 milestone Jun 17, 2023
@basil-conto basil-conto added this to Done in Release 2.20.0 Jun 17, 2023
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bug Existing behavior is incorrect
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@yasuhirokimura @basil-conto