This is related to Bug 4724, but I'm filing it as a separate issue and labeling it a regression because something (probably the more aggressive inlining that was added for 2.058) expands the effects of that bug in ways that break previously working code.  If we can't fix the compiler bug then we need to work around it to avoid an awful regression.

import std.string;

void main() {
    "".indexOf("");
}

dmd -O -inline -release -c test.d
/home/dsimcha/dmd2/linux/bin64/../../src/phobos/std/algorithm.d(2970): Error: function std.string.indexOf!(char,char).indexOf.simpleMindedFind!(__lambda6,const(char)[],const(char)[]).simpleMindedFind is a nested function and cannot be accessed from main

Here's a reduced version that doesn't import any Phobos modules:

void main() {
    "".indexOf("") ;
}

void indexOf(const(char)[] s, const(char)[] sub) {
    find!((dchar a, dchar b){return a == b;})
        (s, sub);
}

void find(alias pred)(const(char)[] haystack, const(char)[] needle) {
     pred(haystack[0], needle[0]);
}

$ dmd -c -O -inline -release test.d
test.d(11): Error: function test.indexOf.find!(delegate pure nothrow @safe bool(dchar a, dchar b)
{
return cast(uint)a == cast(uint)b;
}
).find is a nested function and cannot be accessed from main