Auto merge of #5652 - Eh2406:masquerade_as_nightly_cargo, r=alexcrichton

skip test if not nightly; fix for #5648

closes #5648
The alternative was to use `set_var` to emulate `masquerade_as_nightly_cargo` but we worried that it would not get unset correctly. Although I think each test is its own process, so it should work.

src/bin/cargo/main.rs

@@ -25,6 +25,7 @@ mod commands;
 
 fn main() {
     env_logger::init();
+    cargo::core::maybe_allow_nightly_features();
 
     let mut config = match Config::default() {
         Ok(cfg) => cfg,

src/cargo/core/features.rs

@@ -45,6 +45,7 @@
 //! this writing, a very new feature in Cargo. If the process differs from this
 //! we'll be sure to update this documentation!
 
+use std::cell::Cell;
 use std::env;
 use std::fmt;
 use std::str::FromStr;
@@ -368,9 +369,45 @@ fn channel() -> String {
         .unwrap_or_else(|| String::from("dev"))
 }
 
+thread_local!(
+    static NIGHTLY_FEATURES_ALLOWED: Cell<bool> = Cell::new(false);
+    static ENABLE_NIGHTLY_FEATURES: Cell<bool> = Cell::new(false);
+);
+
+/// This is a little complicated.
+/// This should return false if:
+/// - this is an artifact of the rustc distribution process for "stable" or for "beta"
+/// - this is an `#[test]` that does not opt in with `enable_nightly_features`
+/// - this is a integration test that uses `ProcessBuilder`
+///      that does not opt in with `masquerade_as_nightly_cargo`
+/// This should return true if:
+/// - this is an artifact of the rustc distribution process for "nightly"
+/// - this is being used in the rustc distribution process internally
+/// - this is a cargo executable that was built from source
+/// - this is an `#[test]` that called `enable_nightly_features`
+/// - this is a integration test that uses `ProcessBuilder`
+///       that called `masquerade_as_nightly_cargo`
 fn nightly_features_allowed() -> bool {
-    match &channel()[..] {
-        "nightly" | "dev" => true,
+    if ENABLE_NIGHTLY_FEATURES.with(|c| c.get()) {
+        return true
+    }
+     match &channel()[..] {
+        "nightly" | "dev" => NIGHTLY_FEATURES_ALLOWED.with(|c| c.get()),
         _ => false,
     }
 }
+
+/// Allows nightly features to be enabled for this thread, but only if the
+/// development channel is nightly or dev.
+///
+/// Used by cargo main to ensure that a cargo build from source has nightly features
+pub fn maybe_allow_nightly_features() {
+    NIGHTLY_FEATURES_ALLOWED.with(|c| c.set(true));
+}
+
+/// Forcibly enables nightly features for this thread.
+///
+/// Used by tests to allow the use of nightly features.
+pub fn enable_nightly_features() {
+    ENABLE_NIGHTLY_FEATURES.with(|c| c.set(true));
+}

src/cargo/core/mod.rs

@@ -1,5 +1,6 @@
 pub use self::dependency::Dependency;
 pub use self::features::{CliUnstable, Edition, Feature, Features};
+pub use self::features::{maybe_allow_nightly_features, enable_nightly_features};
 pub use self::manifest::{EitherManifest, VirtualManifest};
 pub use self::manifest::{LibKind, Manifest, Target, TargetKind};
 pub use self::package::{Package, PackageSet};

tests/testsuite/config.rs

@@ -1,4 +1,4 @@
-use cargo::core::Shell;
+use cargo::core::{Shell, enable_nightly_features};
 use cargo::util::config::{self, Config};
 use cargo::util::toml::{self, VecStringOrBool as VSOB};
 use cargo::CargoError;
@@ -45,6 +45,7 @@ fn write_config(config: &str) {
 }
 
 fn new_config(env: &[(&str, &str)]) -> Config {
+    enable_nightly_features(); // -Z advanced-env
     let output = Box::new(fs::File::create(paths::root().join("shell.out")).unwrap());
     let shell = Shell::from_write(output);
     let cwd = paths::root();

tests/testsuite/resolve.rs

@@ -4,7 +4,7 @@ use hamcrest::{assert_that, contains, is_not};
 
 use cargo::core::source::{GitReference, SourceId};
 use cargo::core::dependency::Kind::{self, Development};
-use cargo::core::{Dependency, PackageId, Registry, Summary};
+use cargo::core::{Dependency, PackageId, Registry, Summary, enable_nightly_features};
 use cargo::util::{CargoResult, Config, ToUrl};
 use cargo::core::resolver::{self, Method};
 
@@ -342,6 +342,7 @@ fn test_resolving_maximum_version_with_transitive_deps() {
 
 #[test]
 fn test_resolving_minimum_version_with_transitive_deps() {
+    enable_nightly_features(); // -Z minimal-versions
     // When the minimal-versions config option is specified then the lowest
     // possible version of a package should be selected. "util 1.0.0" can't be
     // selected because of the requirements of "bar", so the minimum version