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Should have a lint for statically detectable overlong bit shifts #17713

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ben0x539 opened this issue Oct 2, 2014 · 2 comments
Closed

Should have a lint for statically detectable overlong bit shifts #17713

ben0x539 opened this issue Oct 2, 2014 · 2 comments
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A-lint Area: Lints (warnings about flaws in source code) such as unused_mut.

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@ben0x539
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ben0x539 commented Oct 2, 2014

Currently overlong bit shifts are undefined behavior because that's how llvm rolls--#10183. But even when they aren't, we should warn on something like x << 24 where x happens to be u8, since it's a useless operation that couldn't possibly return anything interesting.

There's a motivating example and I imagine it'd be a common gotcha since other languages tend to read unadorned integral literals as 32bit ints and then promote the x in x << 24 before doing the actual shift.
@huonw huonw added the A-lint Area: Lints (warnings about flaws in source code) such as unused_mut. label Oct 2, 2014
@hirschenberger hirschenberger mentioned this issue Oct 21, 2014
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hirschenberger added a commit to hirschenberger/rust that referenced this issue Nov 1, 2014
@hirschenberger
Add lint for checking exceeding bitshifts rust-lang#17713
e5058a8
bors added a commit that referenced this issue Nov 3, 2014
@bors
auto merge of #18206 : hirschenberger/rust/issue-17713, r=thestinger
851799d 
Add lint for checking exceeding bitshifts #17713

It also const-evaluates the shift width (RHS) to check more complex shifts like `1u8 << (4+5)`.
The lint-level is set to `Warn` but perhaps it must be `Deny` as in llvm exceeding bitshifts are undefined as @ben0x539 stated in #17713
@hirschenberger
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I think this can be closed, resolved in #18206

@hirschenberger hirschenberger mentioned this issue Nov 3, 2014
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@ben0x539
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ben0x539 commented Nov 4, 2014

Hooray!

@ben0x539 ben0x539 closed this as completed Nov 4, 2014
lnicola pushed a commit to lnicola/rust that referenced this issue Jul 28, 2024
@bors
Auto merge of rust-lang#17713 - alibektas:17710, r=Veykril
552e6c6 
fix: early exit if unresolved field is an index

Fixes rust-lang#17710
RalfJung pushed a commit to RalfJung/rust that referenced this issue Aug 1, 2024
@bors
Auto merge of rust-lang#17713 - alibektas:17710, r=Veykril
1b783b0 
fix: early exit if unresolved field is an index

Fixes rust-lang#17710
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