From bf58fb2458d45d8f451efe78ff46a02f17786727 Mon Sep 17 00:00:00 2001
From: onatozmenn <onatozmen44@gmail.com>
Date: Fri, 31 Jul 2026 18:20:15 +0300
Subject: [PATCH] Say what to press when Run was the wrong button

Twenty-two of the twenty-nine examples are libraries: a module of functions
and test blocks, with no `main` to enter through. Pressing Run on any of them
answered "no `main` found", in red, and stopped there.

The compiler is right. The page was unhelpful: it offers four verbs equally
for every file and then leaves the reader holding a refusal with no next
step, which reads as the page being broken rather than as a fact about the
file they picked.

So the refusal now carries a line saying a file with no `main` is a library,
and a button that runs its tests. The line is the page talking and is written
as such; the compiler's own answer is above it, unchanged.

Matched on the answer rather than on which example is loaded, so it holds for
a program somebody wrote in the editor too, and it survives the compiler
saying it at more length, which deed-lang/deed#789 does.

Co-authored-by: GitHub Copilot <copilot@github.com>
---
 assets/play.js | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/assets/play.js b/assets/play.js
index 1df0d50..5b40a12 100644
--- a/assets/play.js
+++ b/assets/play.js
@@ -208,6 +208,12 @@ function applyEdits(source, edits) {
 }
 
 OUTPUT.addEventListener("click", (event) => {
+  const instead = event.target.closest("button[data-instead]");
+  if (instead) {
+    run(instead.dataset.instead);
+    return;
+  }
+
   const button = event.target.closest("button.apply");
   if (!button) return;
 
@@ -263,6 +269,17 @@ function render(verb, json, source) {
               ? renderDiagnostic(item.diagnostic, source)
               : span("d-error", item.message),
         );
+        // Twenty-two of the twenty-nine examples are libraries: a `module` of
+        // functions and `test` blocks, with no `main` to enter through. The
+        // compiler is right and the page was unhelpful, offering Run for all
+        // of them and then leaving the reader with a refusal and no next step.
+        // This is the page talking, not the compiler.
+        if (!item.ok && !item.diagnostic && /no `main`/.test(item.message ?? "")) {
+          out.push(
+            span("d-note", "  Nothing here is wrong: a file with no `main` is a library.") +
+              `\n  <button type="button" class="apply" data-instead="deed_test">Run its tests instead</button>`,
+          );
+        }
         break;
       case "test":
         out.push(