Bug 21120 – Inconsistent mangling of __init symbol

Testcase: File three.d: ``` module one.two.three; StructTemplate!B instatiation; struct B { } struct StructTemplate(Opts) { void foo() { someTemplate!StructTemplate(); } } template someTemplate(T) { pragma(msg, "_D" ~ T.mangleof[1..$] ~ "6__initZ"); pragma(mangle, "_D" ~ T.mangleof[1..$] ~ "6__initZ") extern immutable typeof(T.init) initializer; void someTemplate() { auto ptr = &initializer; } } ``` > dmd -of=/tmp/wrongmangle.o -c three.d output: _D3one3two5three__T14StructTemplateTSQBjQBiQBh1BZQBe6__initZ > nm /tmp/wrongmangle.o | grep ".*StructTemplate.*__initZ" outputs: 0000000000000270 S __D3one3two5three__T14StructTemplateTS3oneQBjQBi1BZQBf6__initZ U __D3one3two5three__T14StructTemplateTSQBjQBiQBh1BZQBe6__initZ 00000000000001b8 S __D60TypeInfo_S3one3two5three__T14StructTemplateTSQBjQBiQBh1BZQBe6__initZ As you can see there is an undefined symbol: the one that we defined using pragma(mangle). The mangling is just slightly off to what the compiler defines. Note that the defined symbol `__D3one3two5three__T14StructTemplateTS3oneQBjQBi1BZQBf6__initZ` contains "one" twice. Somehow, the repeated identifier detection/encoding does not work. It _does_ work for the TypeInfo symbol (and all other symbols related to `StructTemplate!B`. This inconsistency between `T.mangleof` and the init symbol mangling is a blocker for implementing a druntime hack to access the init symbol similar to this article: http://dpldocs.info/this-week-in-d/Blog.Posted_2020_07_27.html#zero-runtime-classes

@kinke created dlang/dmd pull request #11645 "Fix Issue 21120 - Inconsistent mangling of __init symbol" fixing this issue: - Fix Issue 21120 - Inconsistent mangling of __init symbol The mangling code previously assumed no identifier would ever start at buffer offset 0. Get rid of that assumption by storing offset+1. https://github.com/dlang/dmd/pull/11645

dlang/dmd pull request #11645 "Fix Issue 21120 - Inconsistent mangling of __init symbol" was merged into stable: - 4e863aa3532480abe5832b2448904bdf8e441ddf by Martin Kinkelin: Fix Issue 21120 - Inconsistent mangling of __init symbol The mangling code previously assumed no identifier would ever start at buffer offset 0. Get rid of that assumption by storing offset+1. https://github.com/dlang/dmd/pull/11645

dlang/dmd pull request #11718 "merge stable" was merged into master: - 28c0276975b9c395af0b7a8912a7c1d074166768 by Martin Kinkelin: Fix Issue 21120 - Inconsistent mangling of __init symbol The mangling code previously assumed no identifier would ever start at buffer offset 0. Get rid of that assumption by storing offset+1. https://github.com/dlang/dmd/pull/11718