From 0e88db7db4c09c63ba8a0036d34e72bd48719bd1 Mon Sep 17 00:00:00 2001
From: Jubilee Young <workingjubilee@gmail.com>
Date: Thu, 22 Oct 2020 11:42:44 -0700
Subject: [PATCH] Dogfood {exclusive,half-open} ranges in compiler (nfc)

In particular, this allows us to write more explicit matches that
avoid the pitfalls of using a fully general fall-through case, yet
remain fairly ergonomic. Less logic is in guard cases, more is in
the actual exhaustive case analysis.

No functional changes.
---
 compiler/rustc_lint/src/lib.rs                    | 2 ++
 compiler/rustc_lint/src/unused.rs                 | 6 +++---
 compiler/rustc_middle/src/lib.rs                  | 2 ++
 compiler/rustc_middle/src/ty/inhabitedness/mod.rs | 6 +++---
 compiler/rustc_middle/src/ty/sty.rs               | 4 ++--
 compiler/rustc_session/src/filesearch.rs          | 4 ++--
 6 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
index 1db59bfc39d..d036fbbb67d 100644
--- a/compiler/rustc_lint/src/lib.rs
+++ b/compiler/rustc_lint/src/lib.rs
@@ -35,6 +35,8 @@
 #![feature(never_type)]
 #![feature(nll)]
 #![feature(or_patterns)]
+#![feature(half_open_range_patterns)]
+#![feature(exclusive_range_pattern)]
 #![recursion_limit = "256"]
 
 #[macro_use]
diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index 2409069031d..17f0d5632e6 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -250,13 +250,13 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
                     has_emitted
                 }
                 ty::Array(ty, len) => match len.try_eval_usize(cx.tcx, cx.param_env) {
+                    // If the array is empty we don't lint, to avoid false positives
+                    Some(0) | None => false,
                     // If the array is definitely non-empty, we can do `#[must_use]` checking.
-                    Some(n) if n != 0 => {
+                    Some(n) => {
                         let descr_pre = &format!("{}array{} of ", descr_pre, plural_suffix,);
                         check_must_use_ty(cx, ty, expr, span, descr_pre, descr_post, n as usize + 1)
                     }
-                    // Otherwise, we don't lint, to avoid false positives.
-                    _ => false,
                 },
                 ty::Closure(..) => {
                     cx.struct_span_lint(UNUSED_MUST_USE, span, |lint| {
diff --git a/compiler/rustc_middle/src/lib.rs b/compiler/rustc_middle/src/lib.rs
index fa885ce2e7c..5ccadb7e660 100644
--- a/compiler/rustc_middle/src/lib.rs
+++ b/compiler/rustc_middle/src/lib.rs
@@ -47,6 +47,8 @@
 #![feature(associated_type_bounds)]
 #![feature(rustc_attrs)]
 #![feature(int_error_matching)]
+#![feature(half_open_range_patterns)]
+#![feature(exclusive_range_pattern)]
 #![recursion_limit = "512"]
 
 #[macro_use]
diff --git a/compiler/rustc_middle/src/ty/inhabitedness/mod.rs b/compiler/rustc_middle/src/ty/inhabitedness/mod.rs
index bf1f5b81c9f..2f7707b9498 100644
--- a/compiler/rustc_middle/src/ty/inhabitedness/mod.rs
+++ b/compiler/rustc_middle/src/ty/inhabitedness/mod.rs
@@ -201,13 +201,13 @@ impl<'tcx> TyS<'tcx> {
             ),
 
             Array(ty, len) => match len.try_eval_usize(tcx, param_env) {
+                Some(0) | None => DefIdForest::empty(),
                 // If the array is definitely non-empty, it's uninhabited if
                 // the type of its elements is uninhabited.
-                Some(n) if n != 0 => ty.uninhabited_from(tcx, param_env),
-                _ => DefIdForest::empty(),
+                Some(1..) => ty.uninhabited_from(tcx, param_env),
             },
 
-            // References to uninitialised memory is valid for any type, including
+            // References to uninitialised memory are valid for any type, including
             // uninhabited types, in unsafe code, so we treat all references as
             // inhabited.
             // The precise semantics of inhabitedness with respect to references is currently
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 0fd48d09282..431fa30ed0f 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -1834,10 +1834,10 @@ impl<'tcx> TyS<'tcx> {
             }
             ty::Array(ty, len) => {
                 match len.try_eval_usize(tcx, ParamEnv::empty()) {
+                    Some(0) | None => false,
                     // If the array is definitely non-empty, it's uninhabited if
                     // the type of its elements is uninhabited.
-                    Some(n) if n != 0 => ty.conservative_is_privately_uninhabited(tcx),
-                    _ => false,
+                    Some(1..) => ty.conservative_is_privately_uninhabited(tcx),
                 }
             }
             ty::Ref(..) => {
diff --git a/compiler/rustc_session/src/filesearch.rs b/compiler/rustc_session/src/filesearch.rs
index 12a268d5b1d..55ee4e52082 100644
--- a/compiler/rustc_session/src/filesearch.rs
+++ b/compiler/rustc_session/src/filesearch.rs
@@ -153,14 +153,14 @@ fn find_libdir(sysroot: &Path) -> Cow<'static, str> {
     const SECONDARY_LIB_DIR: &str = "lib";
 
     match option_env!("CFG_LIBDIR_RELATIVE") {
-        Some(libdir) if libdir != "lib" => libdir.into(),
-        _ => {
+        None | Some("lib") => {
             if sysroot.join(PRIMARY_LIB_DIR).join(RUST_LIB_DIR).exists() {
                 PRIMARY_LIB_DIR.into()
             } else {
                 SECONDARY_LIB_DIR.into()
             }
         }
+        Some(libdir) => libdir.into(),
     }
 }