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langref: acknowledge design flaw in the self-hosted compiler

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See tracking issue #13724
This commit is contained in:
Andrew Kelley
2022-11-30 20:23:44 -07:00
parent 9f9f1aadc7
commit 8f079bad1f
1 changed files with 15 additions and 7 deletions
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22
doc/langref.html.in
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@@ -7029,8 +7029,7 @@ test "fibonacci" {
undefined behavior, which is always a compile error if the compiler knows it happened.
But what would have happened if we used a signed integer?
</p>
{#code_begin|test_err|evaluation exceeded 1000 backwards branches#}
{#backend_stage1#}
{#code_begin|syntax#}
const assert = @import("std").debug.assert;
fn fibonacci(index: i32) i32 {
@@ -7045,13 +7044,22 @@ test "fibonacci" {
}
{#code_end#}
<p>
The compiler noticed that evaluating this function at compile-time took a long time,
and thus emitted a compile error and gave up. If the programmer wants to increase
the budget for compile-time computation, they can use a built-in function called
{#link|@setEvalBranchQuota#} to change the default number 1000 to something else.
The compiler is supposed to notice that evaluating this function at
compile-time took more than 1000 branches, and thus emits an error and
gives up. If the programmer wants to increase the budget for compile-time
computation, they can use a built-in function called
{#link|@setEvalBranchQuota#} to change the default number 1000 to
something else.
</p>
<p>
What if we fix the base case, but put the wrong value in the {#syntax#}expect{#endsyntax#} line?
However, there is a <a href="https://github.com/ziglang/zig/issues/13724">design
flaw in the compiler</a> causing it to stack overflow instead of having the proper
behavior here. I'm terribly sorry about that. I hope to get this resolved
before the next release.
</p>
<p>
What if we fix the base case, but put the wrong value in the
{#syntax#}expect{#endsyntax#} line?
</p>
{#code_begin|test_err|reached unreachable#}
const assert = @import("std").debug.assert;