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fix #10840 writeln() of bitfields #10851

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WalterBright merged 1 commit into from
Aug 27, 2025
Merged

fix #10840 writeln() of bitfields #10851

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22 changes: 19 additions & 3 deletions std/format/internal/write.d
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Original file line number Diff line number Diff line change
Expand Up @@ -2546,9 +2546,23 @@ if ((is(T == struct) || is(T == union)) && (hasToString!(T, Char) || !is(Builtin
{
// ignore hidden context pointer
}
else static if (0 < i && T.tupleof[i-1].offsetof == T.tupleof[i].offsetof)
/* https://github.com/dlang/phobos/issues/10840
* handle possible bitfields by doing overlap comparisons
* using bit counts rather than byte counts.
* However, the overlap
* check in general does not take into account staggered unions.
* This can be fixed using the correct algorithm implemented in
* the compiler function dmd.declaration.isOverlappedWith().
Comment on lines +2552 to +2555
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@ibuclaw ibuclaw Aug 27, 2025

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FYI tracking this issue with staggered unions in #10844

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@WalterBright WalterBright Aug 27, 2025

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good!

* For the moment we will not change to that because the `#(overlap ...)` output
* needs to be re-thought, as it was never correct.
*/
else static if (0 < i &&
T.tupleof[i-1].offsetof * 8 + __traits(getBitfieldOffset,T.tupleof[i-1]) ==
T.tupleof[i ].offsetof * 8 + __traits(getBitfieldOffset,T.tupleof[i ]))
{
static if (i == T.tupleof.length - 1 || T.tupleof[i].offsetof != T.tupleof[i+1].offsetof)
static if (i == T.tupleof.length - 1 ||
T.tupleof[i ].offsetof * 8 + __traits(getBitfieldOffset,T.tupleof[i ]) !=
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@ibuclaw ibuclaw Aug 27, 2025

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I didn't realise getBitfieldOffset worked for non-bitfields.

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@WalterBright WalterBright Aug 27, 2025

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I implemented it that way for exactly this reason! It greatly simplifies the overlap logic. You'll see the same thing in the dmd source code, as referenced.

T.tupleof[i+1].offsetof * 8 + __traits(getBitfieldOffset,T.tupleof[i+1]))
{
enum el = separator ~ __traits(identifier, T.tupleof[i]) ~ "}";
put(w, el);
Expand All @@ -2559,7 +2573,9 @@ if ((is(T == struct) || is(T == union)) && (hasToString!(T, Char) || !is(Builtin
put(w, el);
}
}
else static if (i+1 < T.tupleof.length && T.tupleof[i].offsetof == T.tupleof[i+1].offsetof)
else static if (i+1 < T.tupleof.length &&
T.tupleof[i ].offsetof * 8 + __traits(getBitfieldOffset,T.tupleof[i ]) ==
T.tupleof[i+1].offsetof * 8 + __traits(getBitfieldOffset,T.tupleof[i+1]))
{
enum el = (i > 0 ? separator : "") ~ "#{overlap " ~ __traits(identifier, T.tupleof[i]);
put(w, el);
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