use stable cargo for coverage builds

.travis.yml

@@ -14,6 +14,7 @@ matrix:
 before_install:
   - if [[ "$COVERAGE" == "1" ]]; then admin/build-lcov ; fi
   - if [[ "$COVERAGE" == "1" ]]; then gem install coveralls-lcov ; fi
+  - if [[ "$COVERAGE" == "1" ]]; then rustup install stable ; fi
   - if [[ "$COVERAGE" == "1" ]]; then sudo apt-get install libclang-common-3.8-dev llvm-3.8-dev ; fi
 script:
   - RUST_BACKTRACE=1 cargo test

admin/coverage

@@ -3,7 +3,6 @@
 import os
 import glob
 import subprocess
-from os import path
 
 LLVM_PATH = glob.glob('/usr/lib/llvm-3.8/lib/clang/3.8.[0-9]/lib/linux/')[0]
 COVERAGE_OPTIONS = '-Ccodegen-units=1 -Clink-dead-code -Cpasses=insert-gcov-profiling -Zno-landing-pads -L%s -lclang_rt.profile-x86_64' % LLVM_PATH
@@ -23,10 +22,15 @@ def run(which):
     exe = filter(lambda x: '.d' not in x, glob.glob('target/debug/' + which + '-*'))[0]
     sh('./' + exe)
 
+def cargo():
+    # run stable cargo, because nightly is oft-broken
+    out = subprocess.check_output(['rustup', 'run', 'stable', 'rustup', 'which', 'cargo'])
+    return out.strip()
+
 def rustc(*args):
-    exe = ['cargo', 'rustc', '--all-features'] + list(args)
+    exe = [cargo(), 'rustc', '--all-features'] + list(args)
     env = dict(os.environ)
-    env.update(RUSTC_WRAPPER = path.abspath('./admin/coverage-rustc'),
+    env.update(RUSTC_WRAPPER = './admin/coverage-rustc',
                COVERAGE_OPTIONS = COVERAGE_OPTIONS)
     subprocess.check_call(exe, env = env)