Work around rustdoc bugs for proc-macros

Use documentation in /target/doc if /target/$target/doc doesn't exist.

Partially addresses rust-lang#422.

Note: this does _not_ fix the issue mentioned above, it doesn't link
to the right CSS files. See
https://cdn.discordapp.com/attachments/541978667522195476/649031211913838592/unknown.png
for an example.

src/docbuilder/rustwide_builder.rs

@@ -267,7 +267,7 @@ impl RustwideBuilder {
             .build(&self.toolchain, &krate, sandbox)
             .run(|build| {
                 let mut files_list = None;
-                let mut has_docs = false;
+                let (mut has_docs, mut in_target) = (false, false);
                 let mut successful_targets = Vec::new();
 
                 // Do an initial build and then copy the sources in the database
@@ -281,54 +281,43 @@ impl RustwideBuilder {
                         build.host_source_dir(),
                     )?);
 
-                    has_docs = res
-                        .cargo_metadata
-                        .root()
-                        .library_name()
-                        .map(|name| {
-                            build
-                                .host_target_dir()
-                                .join(&res.target)
-                                .join("doc")
-                                .join(name)
-                                .is_dir()
-                        })
-                        .unwrap_or(false);
+                    if let Some(name) = res
+                            .cargo_metadata
+                            .root()
+                            .library_name() {
+                        let host_target = build.host_target_dir();
+                        if host_target.join(&res.target)
+                            .join("doc")
+                            .join(&name)
+                            .is_dir() {
+                            has_docs = true;
+                            in_target = true;
+                        // hack for proc-macro documentation:
+                        // it really should be in target/$target/doc,
+                        // but rustdoc has a bug and puts it in target/doc
+                        } else if host_target.join("doc").join(name).is_dir() {
+                            has_docs = true;
+                        }
+                    }
                 }
 
                 if has_docs {
                     debug!("adding documentation for the default target to the database");
                     self.copy_docs(
                         &build.host_target_dir(),
                         local_storage.path(),
-                        &res.target,
+                        if in_target { &res.target } else { "" },
                         true,
                     )?;
+                    successful_targets.push(DEFAULT_TARGET.to_string());
 
-                    // Then build the documentation for all the targets
-                    for target in TARGETS {
-                        debug!("building package {} {} for {}", name, version, target);
-                        let target_res = self.execute_build(Some(target), &build, &limits)?;
-                        if target_res.successful {
-                            // Cargo is not giving any error and not generating documentation of some crates
-                            // when we use a target compile options. Check documentation exists before
-                            // adding target to successfully_targets.
-                            if build.host_target_dir().join(target).join("doc").is_dir() {
-                                debug!(
-                                    "adding documentation for target {} to the database",
-                                    target
-                                );
-                                self.copy_docs(
-                                    &build.host_target_dir(),
-                                    local_storage.path(),
-                                    target,
-                                    false,
-                                )?;
-                                successful_targets.push(target.to_string());
-                            }
+                    if in_target {
+                        // Then build the documentation for all the targets
+                        for target in TARGETS {
+                            debug!("building package {} {} for {}", name, version, target);
+                            self.build_target(target, &build, &limits, &local_storage.path(), &mut successful_targets)?;
                         }
                     }
-
                     self.upload_docs(&conn, name, version, local_storage.path())?;
                 }
 
@@ -362,6 +351,30 @@ impl RustwideBuilder {
         Ok(res.successful)
     }
 
+    fn build_target(&self, target: &str, build: &Build, limits: &Limits,
+                    local_storage: &Path, successful_targets: &mut Vec<String>) -> Result<()> {
+        let target_res = self.execute_build(Some(target), build, limits)?;
+        if target_res.successful {
+            // Cargo is not giving any error and not generating documentation of some crates
+            // when we use a target compile options. Check documentation exists before
+            // adding target to successfully_targets.
+            if build.host_target_dir().join(target).join("doc").is_dir() {
+                debug!(
+                    "adding documentation for target {} to the database",
+                    target,
+                );
+                self.copy_docs(
+                    &build.host_target_dir(),
+                    local_storage,
+                    target,
+                    false,
+                )?;
+                successful_targets.push(target.to_string());
+            }
+        }
+        Ok(())
+    }
+
     fn execute_build(
         &self,
         target: Option<&str>,