manager: Mark completion using a label

Don't use the open/close state of the issues to mark their completion.
This has friction with dependencies, because you can only add
dependencies on open issues.

Instead, issues are marked as completed using a "Completed" label now.

README.md

@@ -127,7 +127,7 @@ The status of each element is determined as follows:
 
 - **MISSING** when the element has not yet been achieved.
 - **ASSIGNED** when the issue has been assigned to someone.  This means we are making progress!
-- **COMPLETED** when the issue gets closed.  Achievement unlocked!
+- **COMPLETED** when the issue is labelled `Completed`.  Achievement unlocked!
 
 #### Important notes
 There are a few gotchas that you should be aware of:
@@ -136,10 +136,5 @@ There are a few gotchas that you should be aware of:
   unfortunately.  You can force a trigger by editing the issue body or quickly
   adding and then removing the `Stale` label.
 
-- You cannot add dependencies on closed issues via the Forgejo interface.  To
-  model such dependencies, temporarily reopen the dependency issue and close it
-  again after adding the relationship.
-
 - Issues that should no longer be a part of the techtree should either be
-  deleted (looses all tracking) or they can be made inert by removing the
-  `Type/###` label.
+  deleted (looses all tracking) or they can be made inert by closing them.

techtree-manager/src/collect.rs

@@ -77,10 +77,12 @@ fn element_from_issue(issue: &forgejo_api::structs::Issue) -> anyhow::Result<cra
         .context("Issue is missing a title")?
         .to_owned();
 
-    let ty_labels: Vec<_> = issue
+    let labels = issue
         .labels
         .as_ref()
-        .context("Issue does not have any labels")?
+        .context("Issue does not have any labels")?;
+
+    let ty_labels: Vec<_> = labels
         .iter()
         .filter_map(|l| l.name.as_deref())
         .filter(|l| l.starts_with("Type/"))
@@ -100,9 +102,15 @@ fn element_from_issue(issue: &forgejo_api::structs::Issue) -> anyhow::Result<cra
         .unwrap()
         .to_owned();
 
+    let has_completed_label = labels
+        .iter()
+        .any(|l| l.name.as_deref() == Some("Completed"));
+
     let status = match issue.state.context("Missing issue state")? {
         forgejo_api::structs::StateType::Open => {
-            if issue.assignee.is_some()
+            if has_completed_label {
+                crate::tree::ElementStatus::Completed
+            } else if issue.assignee.is_some()
                 || issue
                     .assignees
                     .as_ref()
@@ -114,7 +122,7 @@ fn element_from_issue(issue: &forgejo_api::structs::Issue) -> anyhow::Result<cra
                 crate::tree::ElementStatus::Missing
             }
         }
-        forgejo_api::structs::StateType::Closed => crate::tree::ElementStatus::Completed,
+        forgejo_api::structs::StateType::Closed => anyhow::bail!("Ignoring closed issue!"),
     };
 
     Ok(crate::tree::Element {