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Mangle C main on Wasm #23303

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Merged
thewilsonator merged 1 commit into from
Jun 24, 2026
Merged

Mangle C main on Wasm #23303

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7 changes: 7 additions & 0 deletions changelog/dmd.wasm-c-main-mangle.dd
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@dkorpel dkorpel Jun 24, 2026

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DMD has no WASM target, so this changelog entry shouldn't be here

@QuantumSegfault QuantumSegfault Jun 24, 2026

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So even though the change was upstreamed, it shouldn't be logged?

What about #23293 and #23294?

Either way, this particular one has already been merged. Do you need me to open a PR to delete it?

@dkorpel dkorpel Jun 24, 2026

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It can be logged in LDC's release notes, but the changelog in this repo gets published with dmd releases so users are aware of what changed when upgrading dmd.

Newly reserved version WASI identifiers affect dmd because version = WASIp1 is something dmd now rejects. core.stdc updates for WASM could be relevant if anyone used dmd's bundled druntime sources with LDC, but that sounds very niche so I don't think it's worth mentioning. New mangling of WASM main is irrelevant/confusing for dmd users because it is incapable of generating any WASM code. I would delete it indeed.

Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
`extern(C) main` now mangled correctly on WebAssembly

D now matches the mangling behavior of Clang for C `main` on Wasm targets.

`main` is mangled as either `__main_void` or `__main_argc_argv` as appropriate (unless overriden by `pragma(mangle)`)

This change is useful for both WASI and Emscripten targets, which both expect this.
17 changes: 17 additions & 0 deletions compiler/src/dmd/mangle/package.d
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Original file line number Diff line number Diff line change
Expand Up @@ -727,6 +727,23 @@ public:
buf.writestring(fd.ident.toString());
return;
}

version (IN_LLVM)

@thewilsonator thewilsonator Jun 23, 2026

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cc @ibuclaw for whatever the GCC logic should be

{
import gen.llvmhelpers : isTargetWasm;
bool isWasm = isTargetWasm();
}
else bool isWasm = false;

if (fd.isCMain() && isWasm)
{
if (fd.parameters)
buf.writestring("__main_argc_argv");
else
buf.writestring("__main_void");
return;
}

visit(cast(Declaration)fd);
}

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