test(build-std): isolate tests for asserting complete error messages

For test `basic, an isolated CARGO_HOME environment is used elesewhere
in this test to ensure no extra index updates is performed.
It is achieve by asserting the complete stderr without any wildcard.

Hence we need to provide a `build_std_isolated` method for it.

tests/build-std/main.rs

@@ -25,9 +25,11 @@ use cargo_test_support::{basic_manifest, paths, project, rustc_host, str, Execs}
 use std::env;
 use std::path::Path;
 
-fn enable_build_std(e: &mut Execs, arg: Option<&str>) {
-    e.env_remove("CARGO_HOME");
-    e.env_remove("HOME");
+fn enable_build_std(e: &mut Execs, arg: Option<&str>, isolated: bool) {
+    if !isolated {
+        e.env_remove("CARGO_HOME");
+        e.env_remove("HOME");
+    }
 
     // And finally actually enable `build-std` for now
     let arg = match arg {
@@ -42,17 +44,23 @@ fn enable_build_std(e: &mut Execs, arg: Option<&str>) {
 trait BuildStd: Sized {
     fn build_std(&mut self) -> &mut Self;
     fn build_std_arg(&mut self, arg: &str) -> &mut Self;
+    fn build_std_isolated(&mut self) -> &mut Self;
     fn target_host(&mut self) -> &mut Self;
 }
 
 impl BuildStd for Execs {
     fn build_std(&mut self) -> &mut Self {
-        enable_build_std(self, None);
+        enable_build_std(self, None, false);
         self
     }
 
     fn build_std_arg(&mut self, arg: &str) -> &mut Self {
-        enable_build_std(self, Some(arg));
+        enable_build_std(self, Some(arg), false);
+        self
+    }
+
+    fn build_std_isolated(&mut self) -> &mut Self {
+        enable_build_std(self, None, true);
         self
     }
 
@@ -107,9 +115,12 @@ fn basic() {
         )
         .build();
 
-    p.cargo("check").build_std().target_host().run();
+    // An isolated CARGO_HOME environment is used elesewhere in this test
+    // to ensure no extra index updates is performed.
+    // It is achieve by asserting the complete stderr without any wildcard.
+    p.cargo("check").build_std_isolated().target_host().run();
     p.cargo("build")
-        .build_std()
+        .build_std_isolated()
         .target_host()
         // Importantly, this should not say [UPDATING]
         // There have been multiple bugs where every build triggers and update.
@@ -120,7 +131,7 @@ fn basic() {
 "#]])
         .run();
     p.cargo("run")
-        .build_std()
+        .build_std_isolated()
         .target_host()
         .with_stderr_data(str![[r#"
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
@@ -129,7 +140,7 @@ fn basic() {
 "#]])
         .run();
     p.cargo("test")
-        .build_std()
+        .build_std_isolated()
         .target_host()
         .with_stderr_data(str![[r#"
 [COMPILING] rustc-std-workspace-std [..]
@@ -379,13 +390,11 @@ fn test_proc_macro() {
         .file("src/lib.rs", "")
         .build();
 
-    // Download dependencies first,
-    // so we can compare  `cargo test` output without any wildcard
-    p.cargo("fetch").build_std().run();
     p.cargo("test --lib")
         .env_remove(cargo_util::paths::dylib_path_envvar())
         .build_std()
         .with_stderr_data(str![[r#"
+...
 [COMPILING] foo v0.0.0 ([ROOT]/foo)
 [FINISHED] `test` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [RUNNING] unittests src/lib.rs (target/debug/deps/foo-[HASH])