Don't pass doctest feature by default

src/librustdoc/config.rs

@@ -343,10 +343,7 @@ impl Options {
         let output = matches.opt_str("o")
                             .map(|s| PathBuf::from(&s))
                             .unwrap_or_else(|| PathBuf::from("doc"));
-        let mut cfgs = matches.opt_strs("cfg");
-        if should_test {
-            cfgs.push("doctest".to_string());
-        }
+        let cfgs = matches.opt_strs("cfg");
 
         let extension_css = matches.opt_str("e").map(|s| PathBuf::from(&s));
 

src/librustdoc/test.rs

@@ -64,6 +64,7 @@ pub fn run(options: Options) -> i32 {
 
     let mut cfgs = options.cfgs.clone();
     cfgs.push("rustdoc".to_owned());
+    cfgs.push("doctest".to_owned());
     let config = interface::Config {
         opts: sessopts,
         crate_cfg: config::parse_cfgspecs(cfgs),

src/test/rustdoc-ui/doc-test-doctest-feature.rs

@@ -0,0 +1,15 @@
+// build-pass
+// compile-flags:--test
+// normalize-stdout-test: "src/test/rustdoc-ui" -> "$$DIR"
+
+#![feature(cfg_doctest)]
+
+// Make sure `cfg(doctest)` is set when finding doctests but not inside
+// the doctests.
+
+/// ```
+/// #![feature(cfg_doctest)]
+/// assert!(!cfg!(doctest));
+/// ```
+#[cfg(doctest)]
+pub struct Foo;

src/test/rustdoc-ui/doc-test-doctest-feature.stdout

@@ -0,0 +1,6 @@
+
+running 1 test
+test $DIR/doc-test-doctest-feature.rs - Foo (line 10) ... ok
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
+