Fix EvalBlock in destination block executing destination instead of source

When the cursor is in a named destination block (has name: but no
target:), EvalBlock now searches the buffer for the source block that
targets it and evaluates that instead.

Author: MartyLake

autoload/medieval.vim

@@ -280,6 +280,27 @@ function! medieval#eval(...) abort
         return
     endif
 
+    " If cursor is in a named destination block, find and evaluate its source
+    let opts = s:parseopts(&filetype, start - 1)
+    if has_key(opts, 'name') && !has_key(opts, 'target')
+        call cursor(1, 1)
+        let pat = get(get(g:, 'medieval_option_pat', {}), &filetype, s:optionpat)
+        while 1
+            let srcline = search(pat . s:optspat, 'cW')
+            if !srcline
+                call winrestview(view)
+                return s:error('No source block targeting "' . opts.name . '"')
+            endif
+            call cursor(srcline + 1, 1)
+            if getline(srcline) =~# '\<target:\s*' . opts.name
+                break
+            endif
+        endwhile
+        call call('medieval#eval', a:000)
+        call winrestview(view)
+        return
+    endif
+
     call cursor(start, 1)
 
     let lang = ''

test/medieval.vader

@@ -35,6 +35,26 @@ Execute (Eval source block with named target):
 Then (Output written to named target block):
   AssertEqual 'computed', getline(8)
 
+" === EvalBlock from destination block redirects to source ===
+
+Given markdown (EvalBlock in destination block evaluates its source):
+  <!-- target: dest -->
+  ```sh
+  echo "from source"
+  ```
+
+  <!-- name: dest -->
+  ```
+  old output
+  ```
+
+Execute (Cursor in destination block):
+  8
+  EvalBlock
+
+Then (Source block was evaluated, output written to destination):
+  AssertEqual 'from source', getline(8)
+
 " === :EvalBlock {target} — explicit target argument (doc line 65) ===
 
 Given markdown (Explicit target argument overrides header):