Bug 22050 – -betterC: TypeInfo in speculative template instantiation aborts compilation without error message

This program fails to compile with no output from dmd: ``` import std.algorithm, std.range, std.conv; void foo() { assert(2 == iota(2).map!(n => to!string(n)).length); } ``` Shell session: ``` $ dmd -c bclife.d || echo failed $ dmd -betterC -c bclife.d || echo failed failed $ dmd -betterC -c bclife.d -v |tail -1 import core.internal.lifetime (/home/mipri/dmd2/linux/bin64/../../src/druntime/import/core/internal/lifetime.d) ``` This behavior is seen also with a just-compiled devel dmd. s/string/float/ and it's fine. it silently crashes elsewhere with "".dup instead of to!string(n): ``` semantic2 bclife3 semantic3 bclife3 import core.stdc.string (/home/mipri/dmd2/linux/bin64/../../src/druntime/import/core/stdc/string.d ``` Most other variations that I've tried hit expected betterC errors.

DMD doesn't actually crash but aborts the compilation because of a hidden error (TypeInfo used in dup). The error message is not printed because the instantiation occurs in a speculative context. Reduced example: ============================================ __gshared val = __traits(compiles, to!()); void to()() { auto ti = typeid(char[]); } ============================================ dmd -c -o- -betterC -verrors=spec test.d (spec:1) test.d(6): Error: `TypeInfo` cannot be used with -betterC

The program: import std.algorithm, std.range, std.conv; void foo() { assert(2 == iota(2).map!(n => to!string(n)).length); } extern (C) void main() { foo(); } now compiles and runs successfully with -betterC on master.