make Meta-M with a empty prompt return the contextual module to Main

NEWS.md

@@ -60,6 +60,7 @@ Standard library changes
 
 * Tab complete hints now show in lighter text while typing in the repl. To disable
  set `Base.active_repl.options.hint_tab_completes = false` ([#51229])
+* Meta-M with an empty prompt now returns the contextual module of the REPL to `Main`.
 
 #### SuiteSparse
 

stdlib/REPL/docs/src/index.md

@@ -577,8 +577,8 @@ Main
 
 It is possible to change this contextual module via the function
 `REPL.activate(m)` where `m` is a `Module` or by typing the module in the REPL
-and pressing the keybinding Alt-m (the cursor must be on the module name). The
-active module is shown in the prompt:
+and pressing the keybinding Alt-m (the cursor must be on the module name). The `Main` module can be "activated" with an empty prompt plus the keybinding. The
+active module is shown in the prompt (unless it is `Main`):
 
 ```julia-repl
 julia> using REPL
@@ -598,7 +598,7 @@ julia> Core<Alt-m> # using the keybinding to change module
 
 (Core) julia>
 
-(Core) julia> Main<Alt-m> # going back to Main via keybinding
+(Core) julia> <Alt-m> # going back to Main via keybinding
 
 julia>
 ```

stdlib/REPL/src/LineEdit.jl

@@ -1475,14 +1475,22 @@ current_word_with_dots(s::MIState) = current_word_with_dots(buffer(s))
 
 function activate_module(s::MIState)
  word = current_word_with_dots(s);
- isempty(word) && return beep(s)
- try
- mod = Base.Core.eval(Base.active_module(), Base.Meta.parse(word))
- REPL.activate(mod)
- edit_clear(s)
- catch
+ mod = if isempty(word)
+ edit_insert(s, ' ') # makes the `edit_clear` below actually update the prompt
+ Main
+ else
+ try
+ Base.Core.eval(Base.active_module(), Base.Meta.parse(word))
+ catch
+ nothing
+ end
+ end
+ if !(mod isa Module)
  beep(s)
+ return
  end
+ REPL.activate(mod)
+ edit_clear(s)
 end
 
 history_prev(::EmptyHistoryProvider) = ("", false)