mirror of
https://codeberg.org/ziglang/zig.git
synced 2026-10-29 03:06:10 +08:00
Matthew Lugg
5f74e4f3f8
For generic code, it is far more useful to consider this equivalent to `unreachable`. Meanwhile, it is difficult to accidentally write concrete code which performs this operation, so very little is actually lost from not having a compile error. If we accept that this operation does not trigger a compile error, then it already has the potential to invoke Illegal Behavior today, because uninstantiable types have an unspecified size in memory, so the dereference always potentially exceeds the pointer's provenance. (That said, this only means it is *possible* for the operation to invoke IB, so the langspec should nonetheless explicitly specify that dereferencing a pointer to an uninstantiable type is itself Illegal Behavior.) Storing uninstantiable types into memory does not require any specific language rules, because that operation can never be reached anyway due to it requiring an operand (the RHS of `a = b`) whose type is the store type, which is (by definition) impossible for uninstantiable types. Resolves: https://codeberg.org/ziglang/zig/issues/36247
51 lines
1.6 KiB
Zig
51 lines
1.6 KiB
Zig
const EnumInferred = enum {};
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const EnumExplicit = enum(noreturn) {};
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const EnumNonexhaustive = enum(u8) { _ };
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const U0 = union {};
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const U1 = union(enum) {};
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const U2 = union(enum(noreturn)) {};
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const U3 = union(EnumInferred) {};
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const U4 = union(EnumExplicit) {};
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const U5 = union(EnumNonexhaustive) {};
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export fn init0() void {
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_ = @as(U0, undefined);
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}
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export fn init1() void {
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_ = @as(U1, undefined);
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}
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export fn init2() void {
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_ = @as(U2, undefined);
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}
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export fn init3() void {
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_ = @as(U3, undefined);
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}
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export fn init4() void {
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_ = @as(U4, undefined);
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}
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export fn init5() void {
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_ = @as(U5, undefined);
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}
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// error
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//
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// :13:17: error: expected type 'tmp.U0', found '@TypeOf(undefined)'
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// :13:17: note: cannot coerce to uninstantiable type 'tmp.U0'
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// :5:12: note: union declared here
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// :16:17: error: expected type 'tmp.U1', found '@TypeOf(undefined)'
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// :16:17: note: cannot coerce to uninstantiable type 'tmp.U1'
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// :6:12: note: union declared here
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// :19:17: error: expected type 'tmp.U2', found '@TypeOf(undefined)'
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// :19:17: note: cannot coerce to uninstantiable type 'tmp.U2'
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// :7:12: note: union declared here
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// :22:17: error: expected type 'tmp.U3', found '@TypeOf(undefined)'
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// :22:17: note: cannot coerce to uninstantiable type 'tmp.U3'
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// :8:12: note: union declared here
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// :25:17: error: expected type 'tmp.U4', found '@TypeOf(undefined)'
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// :25:17: note: cannot coerce to uninstantiable type 'tmp.U4'
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// :9:12: note: union declared here
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// :28:17: error: expected type 'tmp.U5', found '@TypeOf(undefined)'
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// :28:17: note: cannot coerce to uninstantiable type 'tmp.U5'
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// :10:12: note: union declared here
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