Add tests that show existing behavior

Author: arlosi

tests/testsuite/main.rs

@@ -182,6 +182,7 @@ mod vendor;
 mod verify_project;
 mod version;
 mod warn_on_failure;
+mod warning_override;
 mod weak_dep_features;
 mod workspaces;
 mod yank;

tests/testsuite/warning_override.rs

@@ -0,0 +1,100 @@
+//! Tests for overriding warning behavior using `build.warnings` config option.
+
+use std::sync::LazyLock;
+
+use cargo_test_support::{cargo_test, project, str, Project};
+use snapbox::data::Inline;
+
+const ALLOW_CLEAN: LazyLock<Inline> = LazyLock::new(|| {
+    str![[r#"
+[CHECKING] foo v0.0.1 ([ROOT]/foo)
+[WARNING] unused variable: `x`
+...
+[WARNING] `foo` (bin "foo") generated 1 warning
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+
+"#]]
+});
+
+const ALLOW_CACHED: LazyLock<Inline> = LazyLock::new(|| {
+    str![[r#"
+[WARNING] unused variable: `x`
+...
+[WARNING] `foo` (bin "foo") generated 1 warning
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+
+"#]]
+});
+
+static WARN: LazyLock<Inline> = LazyLock::new(|| {
+    str![[r#"
+...
+[WARNING] unused variable: `x`
+...
+[WARNING] `foo` (bin "foo") generated 1 warning
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+
+"#]]
+});
+
+const DENY: LazyLock<Inline> = LazyLock::new(|| {
+    str![[r#"
+...
+[WARNING] unused variable: `x`
+...
+[WARNING] `foo` (bin "foo") generated 1 warning
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+
+"#]]
+});
+
+fn make_project(main_src: &str) -> Project {
+    project()
+        .file(
+            "Cargo.toml",
+            &format!(
+                r#"
+                [package]
+                name = "foo"
+                version = "0.0.1"
+                edition = "2021"
+            "#
+            ),
+        )
+        .file("src/main.rs", &format!("fn main() {{ {} }}", main_src))
+        .build()
+}
+
+#[cargo_test]
+fn rustc_caching_allow_first() {
+    let p = make_project("let x = 3;");
+    p.cargo("check").with_stderr_data(ALLOW_CLEAN.clone()).run();
+
+    p.cargo("check").with_stderr_data(DENY.clone()).run();
+}
+
+#[cargo_test]
+fn rustc_caching_deny_first() {
+    let p = make_project("let x = 3;");
+    p.cargo("check").with_stderr_data(DENY.clone()).run();
+
+    p.cargo("check")
+        .with_stderr_data(ALLOW_CACHED.clone())
+        .run();
+}
+
+#[cargo_test]
+fn config() {
+    let p = make_project("let x = 3;");
+    p.cargo("check").with_stderr_data(DENY.clone()).run();
+
+    // CLI has precedence over env.
+    p.cargo("check").with_stderr_data(WARN.clone()).run();
+}
+
+#[cargo_test]
+fn requires_nightly() {
+    // build.warnings has no effect without -Zwarnings.
+    let p = make_project("let x = 3;");
+    p.cargo("check").with_stderr_data(WARN.clone()).run();
+}