Add tests validating the sequence for cargo fix.

This adds a set of tests which validates various edge cases around how
`cargo fix` works in terms of calling `rustc` multiple times. This uses
a replacement of `rustc` so it doesn't depend on the behavior of rustc
itself which is not always stable.

Author: ehuss

src/cargo/util/diagnostic_server.rs

@@ -234,7 +234,7 @@ https://doc.rust-lang.org/edition-guide/editions/transitioning-an-existing-proje
 fn gen_please_report_this_bug_text(url: &str) -> String {
     format!(
         "This likely indicates a bug in either rustc or cargo itself,\n\
-     and we would appreciate a bug report! You're likely to see \n\
+     and we would appreciate a bug report! You're likely to see\n\
      a number of compiler warnings after this message which cargo\n\
      attempted to fix but failed. If you could open an issue at\n\
      {}\n\

tests/testsuite/fix.rs

@@ -6,7 +6,7 @@ use cargo_test_support::git::{self, init};
 use cargo_test_support::paths::{self, CargoPathExt};
 use cargo_test_support::registry::{Dependency, Package};
 use cargo_test_support::tools;
-use cargo_test_support::{basic_manifest, is_nightly, project, Project};
+use cargo_test_support::{basic_manifest, is_nightly, project};
 
 #[cargo_test]
 fn do_not_fix_broken_builds() {
@@ -53,179 +53,6 @@ fn fix_broken_if_requested() {
         .run();
 }
 
-fn rustc_shim_for_cargo_fix() -> Project {
-    // This works as follows:
-    // - Create a `rustc` shim (the "foo" project) which will pretend that the
-    //   verification step fails.
-    // - There is an empty build script so `foo` has `OUT_DIR` to track the steps.
-    // - The first "check", `foo` creates a file in OUT_DIR, and it completes
-    //   successfully with a warning diagnostic to remove unused `mut`.
-    // - rustfix removes the `mut`.
-    // - The second "check" to verify the changes, `foo` swaps out the content
-    //   with something that fails to compile. It creates a second file so it
-    //   won't do anything in the third check.
-    // - cargo fix discovers that the fix failed, and it backs out the changes.
-    // - The third "check" is done to display the original diagnostics of the
-    //   original code.
-    let p = project()
-        .file(
-            "foo/Cargo.toml",
-            r#"
-                [package]
-                name = 'foo'
-                version = '0.1.0'
-                [workspace]
-            "#,
-        )
-        .file(
-            "foo/src/main.rs",
-            r#"
-                use std::env;
-                use std::fs;
-                use std::io::Write;
-                use std::path::{Path, PathBuf};
-                use std::process::{self, Command};
-
-                fn main() {
-                    // Ignore calls to things like --print=file-names and compiling build.rs.
-                    // Also compatible for rustc invocations with `@path` argfile.
-                    let is_lib_rs = env::args_os()
-                        .map(PathBuf::from)
-                        .flat_map(|p| if let Some(p) = p.to_str().unwrap_or_default().strip_prefix("@") {
-                            fs::read_to_string(p).unwrap().lines().map(PathBuf::from).collect()
-                        } else {
-                            vec![p]
-                        })
-                        .any(|l| l == Path::new("src/lib.rs"));
-                    if is_lib_rs {
-                        let path = PathBuf::from(env::var_os("OUT_DIR").unwrap());
-                        let first = path.join("first");
-                        let second = path.join("second");
-                        if first.exists() && !second.exists() {
-                            fs::write("src/lib.rs", b"not rust code").unwrap();
-                            fs::File::create(&second).unwrap();
-                        } else {
-                            fs::File::create(&first).unwrap();
-                        }
-                    }
-                    let status = Command::new("rustc")
-                        .args(env::args().skip(1))
-                        .env_remove("CARGO_MAKEFLAGS")
-                        .status()
-                        .expect("failed to run rustc");
-                    process::exit(status.code().unwrap_or(2));
-                }
-            "#,
-        )
-        .file(
-            "bar/Cargo.toml",
-            r#"
-                [package]
-                name = 'bar'
-                version = '0.1.0'
-                [workspace]
-            "#,
-        )
-        .file("bar/build.rs", "fn main() {}")
-        .file(
-            "bar/src/lib.rs",
-            r#"
-                pub fn foo() {
-                    let mut x = 3;
-                    drop(x);
-                }
-            "#,
-        )
-        .build();
-
-    // Build our rustc shim
-    p.cargo("build").cwd("foo").run();
-
-    p
-}
-
-#[cargo_test]
-fn broken_fixes_backed_out() {
-    let p = rustc_shim_for_cargo_fix();
-    // Attempt to fix code, but our shim will always fail the second compile.
-    p.cargo("fix --allow-no-vcs --lib")
-        .cwd("bar")
-        .env("__CARGO_FIX_YOLO", "1")
-        .env("RUSTC", p.root().join("foo/target/debug/foo"))
-        .with_stderr_contains(
-            "warning: failed to automatically apply fixes suggested by rustc \
-             to crate `bar`\n\
-             \n\
-             after fixes were automatically applied the compiler reported \
-             errors within these files:\n\
-             \n  \
-             * src/lib.rs\n\
-             \n\
-             This likely indicates a bug in either rustc or cargo itself,\n\
-             and we would appreciate a bug report! You're likely to see \n\
-             a number of compiler warnings after this message which cargo\n\
-             attempted to fix but failed. If you could open an issue at\n\
-             https://github.com/rust-lang/rust/issues\n\
-             quoting the full output of this command we'd be very appreciative!\n\
-             Note that you may be able to make some more progress in the near-term\n\
-             fixing code with the `--broken-code` flag\n\
-             \n\
-             The following errors were reported:\n\
-             error: expected one of `!` or `::`, found `rust`\n\
-             ",
-        )
-        .with_stderr_contains("Original diagnostics will follow.")
-        .with_stderr_contains("[WARNING] variable does not need to be mutable")
-        .with_stderr_does_not_contain("[..][FIXED][..]")
-        .run();
-
-    // Make sure the fix which should have been applied was backed out
-    assert!(p.read_file("bar/src/lib.rs").contains("let mut x = 3;"));
-}
-
-#[cargo_test]
-fn broken_clippy_fixes_backed_out() {
-    let p = rustc_shim_for_cargo_fix();
-    // Attempt to fix code, but our shim will always fail the second compile.
-    // Also, we use `clippy` as a workspace wrapper to make sure that we properly
-    // generate the report bug text.
-    p.cargo("fix --allow-no-vcs --lib")
-        .cwd("bar")
-        .env("__CARGO_FIX_YOLO", "1")
-        .env("RUSTC", p.root().join("foo/target/debug/foo"))
-        //  We can't use `clippy` so we use a `rustc` workspace wrapper instead
-        .env("RUSTC_WORKSPACE_WRAPPER", tools::wrapped_clippy_driver())
-        .with_stderr_contains(
-            "warning: failed to automatically apply fixes suggested by rustc \
-             to crate `bar`\n\
-             \n\
-             after fixes were automatically applied the compiler reported \
-             errors within these files:\n\
-             \n  \
-             * src/lib.rs\n\
-             \n\
-             This likely indicates a bug in either rustc or cargo itself,\n\
-             and we would appreciate a bug report! You're likely to see \n\
-             a number of compiler warnings after this message which cargo\n\
-             attempted to fix but failed. If you could open an issue at\n\
-             https://github.com/rust-lang/rust-clippy/issues\n\
-             quoting the full output of this command we'd be very appreciative!\n\
-             Note that you may be able to make some more progress in the near-term\n\
-             fixing code with the `--broken-code` flag\n\
-             \n\
-             The following errors were reported:\n\
-             error: expected one of `!` or `::`, found `rust`\n\
-             ",
-        )
-        .with_stderr_contains("Original diagnostics will follow.")
-        .with_stderr_contains("[WARNING] variable does not need to be mutable")
-        .with_stderr_does_not_contain("[..][FIXED][..]")
-        .run();
-
-    // Make sure the fix which should have been applied was backed out
-    assert!(p.read_file("bar/src/lib.rs").contains("let mut x = 3;"));
-}
-
 #[cargo_test]
 fn fix_path_deps() {
     let p = project()