Rather than hardcoding the paths to /usr/include, allow the user to set
the path to their libc headers. This is particularly important for
environments which may not use the traditional layout (e.g. exherbo) or
for builds which wish to build against an out-of-tree, non-system
installed libc for a Unix target which does not match the host system
(i.e. foreign cross-compilation).
Fixes a general category (pun intended) of scalar-alignment bugs
surrounding exchanging non-scalar-aligned indices between views and
for slicing.
SE-0180 unifies the Index type of String and all its views and allows
non-scalar-aligned indices to be used across views. In order to
guarantee behavior, we often have to check and perform scalar
alignment. To speed up these checks, we allocate a bit denoting
known-to-be-aligned, so that the alignment check can skip the
load. The below shows what views need to check for alignment before
they can operate, and whether the indices they produce are aligned.
┌───────────────╥────────────────────┬──────────────────────────┐
│ View ║ Requires Alignment │ Produces Aligned Indices │
╞═══════════════╬════════════════════╪══════════════════════════╡
│ Native UTF8 ║ no │ no │
├───────────────╫────────────────────┼──────────────────────────┤
│ Native UTF16 ║ yes │ no │
╞═══════════════╬════════════════════╪══════════════════════════╡
│ Foreign UTF8 ║ yes │ no │
├───────────────╫────────────────────┼──────────────────────────┤
│ Foreign UTF16 ║ no │ no │
╞═══════════════╬════════════════════╪══════════════════════════╡
│ UnicodeScalar ║ yes │ yes │
├───────────────╫────────────────────┼──────────────────────────┤
│ Character ║ yes │ yes │
└───────────────╨────────────────────┴──────────────────────────┘
The "requires alignment" applies to any operation taking a
String.Index that's not defined entirely in terms of other operations
taking a String.Index. These include:
* index(after:)
* index(before:)
* subscript
* distance(from:to:) (since `to` is compared against directly)
* UTF16View._nativeGetOffset(for:)
ICU will return different results if we call with an offset into a
code unit buffer vs if we slice the buffer first and provide an offset
of zero. Slicing more closely models the semantics of SE-0180, so use
that.
Test case coming in subsequent commit enforcing index
scalar-alignment.
* Update Decimal.swift
Fix `Decimal.magnitude` so that `Decimal.nan.magnitude` is no longer incorrectly `0`.
Port changes from apple/swift-corelibs-foundation#1759, crucially correcting an error where `(0 as Decimal).doubleValue` returned `.nan`.
* [gardening] Zap indentation error
* Add test for `Decimal.nan.magnitude`
* Apply reviewer suggestion
Clean up `doubleValue`
This was an ABI break, since it didn't make it into 5.0. Using _read here is unimportant, so we're just going to revert rather than try being fancy.
This reverts commit 04586e3916.
