Add -Zcheck-target-cfgs in preparation for linting

Author: Urgau

src/cargo/core/features.rs

@@ -784,6 +784,7 @@ unstable_cli_options!(
     #[serde(deserialize_with = "deserialize_comma_separated_list")]
     build_std_features: Option<Vec<String>>  = ("Configure features enabled for the standard library itself when building the standard library"),
     cargo_lints: bool = ("Enable the `[lints.cargo]` table"),
+    check_target_cfgs: bool = ("Enable unexpected cfgs checking in `[target.'cfg(...)']` tables"),
     checksum_freshness: bool = ("Use a checksum to determine if output is fresh rather than filesystem mtime"),
     codegen_backend: bool = ("Enable the `codegen-backend` option in profiles in .cargo/config.toml file"),
     config_include: bool = ("Enable the `include` key in config files"),
@@ -1292,6 +1293,7 @@ impl CliUnstable {
             "build-std" => self.build_std = Some(parse_list(v)),
             "build-std-features" => self.build_std_features = Some(parse_list(v)),
             "cargo-lints" => self.cargo_lints = parse_empty(k, v)?,
+            "check-target-cfgs" => self.check_target_cfgs = parse_empty(k, v)?,
             "codegen-backend" => self.codegen_backend = parse_empty(k, v)?,
             "config-include" => self.config_include = parse_empty(k, v)?,
             "direct-minimal-versions" => self.direct_minimal_versions = parse_empty(k, v)?,

src/doc/src/reference/unstable.md

@@ -126,6 +126,7 @@ Each new feature described below should explain how to use it.
     * [native-completions](#native-completions) --- Move cargo shell completions to native completions.
     * [warnings](#warnings) --- controls warning behavior; options for allowing or denying warnings.
     * [Package message format](#package-message-format) --- Message format for `cargo package`.
+    * [check-target-cfgs](#check-target-cfgs) --- Allows checking unexpected cfgs in `[target.'cfg(...)']`
 
 ## allow-features
 
@@ -1915,6 +1916,31 @@ When new editions are introduced, the `unstable-editions` feature is required un
 
 The special "future" edition is a home for new features that are under development, and is permanently unstable. The "future" edition also has no new behavior by itself. Each change in the future edition requires an opt-in such as a `#![feature(...)]` attribute.
 
+## check-target-cfgs
+
+* Tracking Issue: [#00000](https://github.com/rust-lang/cargo/issues/00000)
+
+This feature checks for unexpected cfgs in `[target.'cfg(...)']` entries, based
+on `rustc --print=check-cfg`.
+
+```sh
+cargo check -Zcheck-target-cfgs
+```
+
+It follows the lint Rust `unexpected_cfgs` lint configuration:
+
+```toml
+[target.'cfg(foo)'.dependencies]
+cfg-if = "1.0"
+
+[lints.cargo.unexpected_cfgs]
+level = "deny"
+
+[lints.rust.unexpected_cfgs]
+level = "warn"
+check-cfg = ['cfg(foo)']
+```
+
 # Stabilized and removed features
 
 ## Compile progress

tests/testsuite/cargo/z_help/stdout.term.svg

@@ -817,3 +817,57 @@ fn cfg_booleans_rustflags_no_effect() {
 "#]])
         .run();
 }
+
+#[cargo_test(nightly, reason = "--print=check-cfg is unstable in rustc")]
+fn unexpected_cfgs_target() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "a"
+                version = "0.0.1"
+                edition = "2015"
+                authors = []
+
+                [target."cfg(any(windows, unix))".dependencies]
+                b = { path = 'b' }
+
+                [target."cfg(any(foo, all(bar)))".dependencies]
+                b = { path = 'b' }
+
+                [target.'cfg(unix = "zoo")'.dependencies]
+                b = { path = 'b' }
+                c = { path = 'c' }
+
+                [target.'cfg(not(windows = ""))'.dependencies]
+                b = { path = 'b' }
+            "#,
+        )
+        .file(
+            ".cargo/config.toml",
+            r#"
+                [target."cfg(any(windows, unix))"]
+                [target."cfg(any(foo, all(bar)))"]
+                [target.'cfg(unix = "zoo")']
+                [target.'cfg(not(windows = ""))']
+            "#,
+        )
+        .file("src/lib.rs", "extern crate b;")
+        .file("b/Cargo.toml", &basic_manifest("b", "0.0.1"))
+        .file("b/src/lib.rs", "")
+        .file("c/Cargo.toml", &basic_manifest("c", "0.0.1"))
+        .file("c/src/lib.rs", "")
+        .build();
+
+    p.cargo("check -Zcheck-target-cfgs")
+        .masquerade_as_nightly_cargo(&["requires -Zcheck-target-cfgs"])
+        .with_stderr_data(str![[r#"
+[LOCKING] 2 packages to latest compatible versions
+[CHECKING] b v0.0.1 ([ROOT]/foo/b)
+[CHECKING] a v0.0.1 ([ROOT]/foo)
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+
+"#]])
+        .run();
+}