Wire up unstable rustc --check-cfg to rustdoc

src/doc/rustdoc/src/unstable-features.md

@@ -512,3 +512,17 @@ crate being documented (`foobar`) and a path to output the calls
 
 To scrape examples from test code, e.g. functions marked `#[test]`, then
 add the `--scrape-tests` flag.
+
+### `--check-cfg`: check configuration flags
+
+This flag accepts the same values as `rustc --check-cfg`, and uses it to check configuration flags.
+
+Using this flag looks like this:
+
+```bash
+$ rustdoc src/lib.rs -Z unstable-options \
+    --check-cfg='names()' --check-cfg='values(feature, "foo", "bar")'
+```
+
+The example above check every well known names (`target_os`, `doc`, `test`, ... via `names()`)
+and check the values of `feature`: `foo` and `bar`.

src/librustdoc/config.rs

@@ -80,6 +80,8 @@ crate struct Options {
     crate extern_strs: Vec<String>,
     /// List of `cfg` flags to hand to the compiler. Always includes `rustdoc`.
     crate cfgs: Vec<String>,
+    /// List of check cfg flags to hand to the compiler.
+    crate check_cfgs: Vec<String>,
     /// Codegen options to hand to the compiler.
     crate codegen_options: CodegenOptions,
     /// Codegen options strings to hand to the compiler.
@@ -172,6 +174,7 @@ impl fmt::Debug for Options {
             .field("libs", &self.libs)
             .field("externs", &FmtExterns(&self.externs))
             .field("cfgs", &self.cfgs)
+            .field("check-cfgs", &self.check_cfgs)
             .field("codegen_options", &"...")
             .field("debugging_options", &"...")
             .field("target", &self.target)
@@ -506,6 +509,7 @@ impl Options {
         };
 
         let cfgs = matches.opt_strs("cfg");
+        let check_cfgs = matches.opt_strs("check-cfg");
 
         let extension_css = matches.opt_str("e").map(|s| PathBuf::from(&s));
 
@@ -677,6 +681,7 @@ impl Options {
             externs,
             extern_strs,
             cfgs,
+            check_cfgs,
             codegen_options,
             codegen_options_strs,
             debugging_opts,

src/librustdoc/core.rs

@@ -192,6 +192,7 @@ crate fn create_config(
         libs,
         externs,
         mut cfgs,
+        check_cfgs,
         codegen_options,
         debugging_opts,
         target,
@@ -219,6 +220,7 @@ crate fn create_config(
         // these are definitely not part of rustdoc, but we want to warn on them anyway.
         rustc_lint::builtin::RENAMED_AND_REMOVED_LINTS.name.to_string(),
         rustc_lint::builtin::UNKNOWN_LINTS.name.to_string(),
+        rustc_lint::builtin::UNEXPECTED_CFGS.name.to_string(),
     ];
     lints_to_show.extend(crate::lint::RUSTDOC_LINTS.iter().map(|lint| lint.name.to_string()));
 
@@ -253,7 +255,7 @@ crate fn create_config(
     interface::Config {
         opts: sessopts,
         crate_cfg: interface::parse_cfgspecs(cfgs),
-        crate_check_cfg: interface::parse_check_cfg(vec![]),
+        crate_check_cfg: interface::parse_check_cfg(check_cfgs),
         input,
         input_path: cpath,
         output_file: None,

src/librustdoc/doctest.rs

@@ -91,7 +91,7 @@ crate fn run(options: RustdocOptions) -> Result<(), ErrorReported> {
     let config = interface::Config {
         opts: sessopts,
         crate_cfg: interface::parse_cfgspecs(cfgs),
-        crate_check_cfg: interface::parse_check_cfg(vec![]),
+        crate_check_cfg: interface::parse_check_cfg(options.check_cfgs.clone()),
         input,
         input_path: None,
         output_file: None,
@@ -321,6 +321,12 @@ fn run_test(
     for cfg in &rustdoc_options.cfgs {
         compiler.arg("--cfg").arg(&cfg);
     }
+    if !rustdoc_options.check_cfgs.is_empty() {
+        compiler.arg("-Z").arg("unstable-options");
+        for check_cfg in &rustdoc_options.check_cfgs {
+            compiler.arg("--check-cfg").arg(&check_cfg);
+        }
+    }
     if let Some(sysroot) = rustdoc_options.maybe_sysroot {
         compiler.arg("--sysroot").arg(sysroot);
     }

src/librustdoc/lib.rs

@@ -259,6 +259,7 @@ fn opts() -> Vec<RustcOptGroup> {
             o.optmulti("L", "library-path", "directory to add to crate search path", "DIR")
         }),
         stable("cfg", |o| o.optmulti("", "cfg", "pass a --cfg to rustc", "")),
+        unstable("check-cfg", |o| o.optmulti("", "check-cfg", "pass a --check-cfg to rustc", "")),
         stable("extern", |o| o.optmulti("", "extern", "pass an --extern to rustc", "NAME[=PATH]")),
         unstable("extern-html-root-url", |o| {
             o.optmulti(

src/test/rustdoc-ui/check-cfg-test.rs

@@ -0,0 +1,12 @@
+// check-pass
+// compile-flags: --test --nocapture --check-cfg=values(feature,"test") -Z unstable-options
+// normalize-stderr-test: "src/test/rustdoc-ui" -> "$$DIR"
+// normalize-stdout-test: "src/test/rustdoc-ui" -> "$$DIR"
+// normalize-stdout-test "finished in \d+\.\d+s" -> "finished in $$TIME"
+
+/// The doctest will produce a warning because feature invalid is unexpected
+/// ```
+/// #[cfg(feature = "invalid")]
+/// assert!(false);
+/// ```
+pub struct Foo;

src/test/rustdoc-ui/check-cfg-test.stderr

@@ -0,0 +1,11 @@
+warning: unexpected `cfg` condition value
+  --> $DIR/check-cfg-test.rs:9:7
+   |
+LL | #[cfg(feature = "invalid")]
+   |       ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(unexpected_cfgs)]` on by default
+   = note: expected values for `feature` are: test
+
+warning: 1 warning emitted
+

src/test/rustdoc-ui/check-cfg-test.stdout

@@ -0,0 +1,6 @@
+
+running 1 test
+test $DIR/check-cfg-test.rs - Foo (line 8) ... ok
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
+

src/test/rustdoc-ui/check-cfg-unstable.rs

@@ -0,0 +1,2 @@
+// check-fail
+// compile-flags: --check-cfg=names()

src/test/rustdoc-ui/check-cfg-unstable.stderr

@@ -0,0 +1,2 @@
+error: the `-Z unstable-options` flag must also be passed to enable the flag `check-cfg`
+

src/test/rustdoc-ui/check-cfg.rs

@@ -0,0 +1,7 @@
+// check-pass
+// compile-flags: --check-cfg=names() -Z unstable-options
+
+/// uniz is nor a builtin nor pass as arguments so is unexpected
+#[cfg(uniz)]
+//~^ WARNING unexpected `cfg` condition name
+pub struct Bar;

src/test/rustdoc-ui/check-cfg.stderr

@@ -0,0 +1,10 @@
+warning: unexpected `cfg` condition name
+  --> $DIR/check-cfg.rs:5:7
+   |
+LL | #[cfg(uniz)]
+   |       ^^^^ help: did you mean: `unix`
+   |
+   = note: `#[warn(unexpected_cfgs)]` on by default
+
+warning: 1 warning emitted
+