x build src/tools/cargo builds the compiler

[jyn514]

Cargo builds on stable. Building the compiler seems wrong.

Changing ToolRustc to ToolBootstrap avoids building the compiler, but gives an error when using --stage 1 or --stage 2 with cargo. I think in some sense that's right? Cargo should be the same regardless of the stage you use to build it.

ToolRustc -> ToolBootstrap

diff --git a/src/bootstrap/test.rs b/src/bootstrap/test.rs
index bc851568f89..a5cd6315b1a 100644
--- a/src/bootstrap/test.rs
+++ b/src/bootstrap/test.rs
@@ -273,7 +273,7 @@ fn run(self, builder: &Builder<'_>) {
         let mut cargo = tool::prepare_tool_cargo(
             builder,
             compiler,
-            Mode::ToolRustc,
+            Mode::ToolBootstrap,
             self.host,
             "test",
             "src/tools/cargo",
diff --git a/src/bootstrap/tool.rs b/src/bootstrap/tool.rs
index 3b30e6de12a..d775e3b4e55 100644
--- a/src/bootstrap/tool.rs
+++ b/src/bootstrap/tool.rs
@@ -609,7 +609,7 @@ fn run(self, builder: &Builder<'_>) -> PathBuf {
                 compiler: self.compiler,
                 target: self.target,
                 tool: "cargo",
-                mode: Mode::ToolRustc,
+                mode: Mode::ToolBootstrap,
                 path: "src/tools/cargo",
                 is_optional_tool: false,
                 source_type: SourceType::Submodule,
@@ -624,7 +624,7 @@ fn run(self, builder: &Builder<'_>) -> PathBuf {
                 compiler: self.compiler,
                 target: self.target,
                 tool: name,
-                mode: Mode::ToolRustc,
+                mode: Mode::ToolBootstrap,
                 path,
                 is_optional_tool: true,
                 source_type: SourceType::Submodule,

cc @Mark-Simulacrum: I wonder if we should make this change and give a warning when using --stage with cargo.

I found this in #97268.

@rustbot label +A-rustbuild +A-contributor-roadblock

[jyn514]

src/tools/rust-demangler has the same issue.

[ehuss]

Can you say more about why you would want to change this? I would prefer to keep cargo building with the latest tip of the compiler to ensure that there aren't any regressions. Also, the testsuite depends on some nightly-only things, which I think would be a problem if rustc weren't built.

[jyn514]

@ehuss building the compiler is slow. When I need to replicate CI failures that involve cargo, it's frustrating to have to wait for a full compiler build first, even when using --stage 0.

I would prefer to keep cargo building with the latest tip of the compiler to ensure that there aren't any regressions. Also, the testsuite depends on some nightly-only things, which I think would be a problem if rustc weren't built.

Ok - maybe we should still allow using --stage 2 and pass that in CI, but fix --stage 0 not to build the compiler? I think cargo is only using feature(test) and a few other library features, which we can allow by using Mode::ToolStd. If nothing else, build cargo shouldn't require anything nightly and we can only build rustc crates when using test cargo.