Be more consistent about detecting CI.

crates/resolver-tests/tests/resolve.rs

@@ -2,7 +2,7 @@ use std::env;
 
 use cargo::core::dependency::Kind;
 use cargo::core::{enable_nightly_features, Dependency};
-use cargo::util::Config;
+use cargo::util::{is_ci, Config};
 
 use resolver_tests::{
     assert_contains, assert_same, dep, dep_kind, dep_loc, dep_req, dep_req_kind, loc_names, names,
@@ -22,7 +22,7 @@ use proptest::prelude::*;
 proptest! {
     #![proptest_config(ProptestConfig {
         max_shrink_iters:
-            if env::var("CI").is_ok() || !atty::is(atty::Stream::Stderr) {
+            if is_ci() || !atty::is(atty::Stream::Stderr) {
                 // This attempts to make sure that CI will fail fast,
                 0
             } else {

src/cargo/util/mod.rs

@@ -82,3 +82,8 @@ pub fn validate_package_name(name: &str, what: &str, help: &str) -> CargoResult<
     }
     Ok(())
 }
+
+/// Whether or not this running in a Continuous Integration environment.
+pub fn is_ci() -> bool {
+    std::env::var("CI").is_ok() || std::env::var("TF_BUILD").is_ok()
+}

src/cargo/util/progress.rs

@@ -3,7 +3,7 @@ use std::env;
 use std::time::{Duration, Instant};
 
 use crate::core::shell::Verbosity;
-use crate::util::{CargoResult, Config};
+use crate::util::{is_ci, CargoResult, Config};
 
 use unicode_width::UnicodeWidthChar;
 
@@ -45,7 +45,7 @@ impl<'cfg> Progress<'cfg> {
             Ok(term) => term == "dumb",
             Err(_) => false,
         };
-        if cfg.shell().verbosity() == Verbosity::Quiet || dumb || env::var("CI").is_ok() {
+        if cfg.shell().verbosity() == Verbosity::Quiet || dumb || is_ci() {
             return Progress { state: None };
         }
 

tests/testsuite/support/mod.rs

@@ -118,7 +118,7 @@ use std::time::{self, Duration};
 use std::usize;
 
 use cargo;
-use cargo::util::{CargoResult, ProcessBuilder, ProcessError, Rustc};
+use cargo::util::{is_ci, CargoResult, ProcessBuilder, ProcessError, Rustc};
 use filetime;
 use serde_json::{self, Value};
 use url::Url;
@@ -855,7 +855,7 @@ impl Execs {
     fn match_process(&self, process: &ProcessBuilder) -> MatchResult {
         println!("running {}", process);
         let res = if self.stream_output {
-            if env::var("CI").is_ok() {
+            if is_ci() {
                 panic!("`.stream()` is for local debugging")
             }
             process.exec_with_streaming(
@@ -1746,7 +1746,7 @@ pub fn is_coarse_mtime() -> bool {
     // This should actually be a test that `$CARGO_TARGET_DIR` is on an HFS
     // filesystem, (or any filesystem with low-resolution mtimes). However,
     // that's tricky to detect, so for now just deal with CI.
-    cfg!(target_os = "macos") && (env::var("CI").is_ok() || env::var("TF_BUILD").is_ok())
+    cfg!(target_os = "macos") && is_ci()
 }
 
 /// Some CI setups are much slower then the equipment used by Cargo itself.
@@ -1772,6 +1772,10 @@ pub fn clippy_is_available() -> bool {
 
 #[cfg(windows)]
 pub fn symlink_supported() -> bool {
+    if is_ci() {
+        // We want to be absolutely sure this runs on CI.
+        return true;
+    }
     let src = paths::root().join("symlink_src");
     fs::write(&src, "").unwrap();
     let dst = paths::root().join("symlink_dst");