Auto merge of #48209 - kennytm:try-fix-48116, r=alexcrichton

Try to fix 48116 and 48192

The bug #48116 happens because of a misoptimization of the `import_path_to_string` function, where a `names` slice is empty but the `!names.is_empty()` branch is executed.

https://github.com/rust-lang/rust/blob/4d2d3fc5dadf894a8ad709a5860a549f2c0b1032/src/librustc_resolve/resolve_imports.rs#L1015-L1042

Yesterday, @eddyb had locally reproduced the bug, and [came across the `position` function](https://mozilla.logbot.info/rust-infra/20180214#c14296834) where the `assume()` call is found to be suspicious. We have *not* concluded that this `assume()` causes #48116, but given [the reputation of `assume()`](https://github.com/rust-lang/rust/pull/45501#issuecomment-340159627), this seems higher relevant. Here we try to see if commenting it out can fix the errors.

Later @alexcrichton has bisected and found a potential bug [in the LLVM side](https://github.com/rust-lang/rust/issues/48116#issuecomment-365624777). We are currently testing if reverting that LLVM commit is enough to stop the bug. If true, this PR can be reverted (keep the `assume()`) and we could backport the LLVM patch instead.

(This PR also includes an earlier commit from #48127 for help debugging ICE happening in compile-fail/parse-fail tests.)

The PR also reverts #48059, which seems to cause #48192.

r? @alexcrichton
cc @eddyb, @arthurprs (#47333)

1 files changed, 5 insertions, 22 deletions

diff --git a/src/bootstrap/builder.rs b/src/bootstrap/builder.rs
index 74dd4a6fa01..03630dfbed3 100644
--- a/src/bootstrap/builder.rs
+++ b/src/bootstrap/builder.rs
@@ -600,25 +600,9 @@ impl<'a> Builder<'a> {
         //
         // FIXME: the guard against msvc shouldn't need to be here
         if !target.contains("msvc") {
-            let ccache = self.config.ccache.as_ref();
-            let ccacheify = |s: &Path| {
-                let ccache = match ccache {
-                    Some(ref s) => s,
-                    None => return s.display().to_string(),
-                };
-                // FIXME: the cc-rs crate only recognizes the literal strings
-                // `ccache` and `sccache` when doing caching compilations, so we
-                // mirror that here. It should probably be fixed upstream to
-                // accept a new env var or otherwise work with custom ccache
-                // vars.
-                match &ccache[..] {
-                    "ccache" | "sccache" => format!("{} {}", ccache, s.display()),
-                    _ => s.display().to_string(),
-                }
-            };
-            let cc = ccacheify(&self.cc(target));
-            cargo.env(format!("CC_{}", target), &cc)
-                 .env("CC", &cc);
+            let cc = self.cc(target);
+            cargo.env(format!("CC_{}", target), cc)
+                 .env("CC", cc);
 
             let cflags = self.cflags(target).join(" ");
             cargo.env(format!("CFLAGS_{}", target), cflags.clone())
@@ -633,9 +617,8 @@ impl<'a> Builder<'a> {
             }
 
             if let Ok(cxx) = self.cxx(target) {
-                let cxx = ccacheify(&cxx);
-                cargo.env(format!("CXX_{}", target), &cxx)
-                     .env("CXX", &cxx)
+                cargo.env(format!("CXX_{}", target), cxx)
+                     .env("CXX", cxx)
                      .env(format!("CXXFLAGS_{}", target), cflags.clone())
                      .env("CXXFLAGS", cflags);
             }