let rustdoc print the crate version into docs

src/librustdoc/lib.rs

@@ -243,6 +243,9 @@ pub fn opts() -> Vec<RustcOptGroup> {
         unstable("display-warnings", |o| {
             o.optflag("", "display-warnings", "to print code warnings when testing doc")
         }),
+        unstable("crate-version", |o| {
+            o.optopt("", "crate-version", "crate version to print into documentation", "VERSION")
+        }),
     ]
 }
 
@@ -460,6 +463,7 @@ where R: 'static + Send, F: 'static + Send + FnOnce(Output) -> R {
     let triple = matches.opt_str("target");
     let maybe_sysroot = matches.opt_str("sysroot").map(PathBuf::from);
     let crate_name = matches.opt_str("crate-name");
+    let crate_version = matches.opt_str("crate-version");
     let plugin_path = matches.opt_str("plugin-path");
 
     let cr = PathBuf::from(cratefile);
@@ -484,6 +488,8 @@ where R: 'static + Send, F: 'static + Send + FnOnce(Output) -> R {
             krate.name = name
         }
 
+        krate.version = crate_version;
+
         // Process all of the crate attributes, extracting plugin metadata along
         // with the passes which we are supposed to run.
         for attr in krate.module.as_ref().unwrap().attrs.lists("doc") {