From 72dda46fb949450ad9d2c9cb4c2b71e7194c3bf0 Mon Sep 17 00:00:00 2001
From: Ian Butterworth <i.r.butterworth@gmail.com>
Date: Thu, 7 Sep 2023 13:29:19 +0100
Subject: [PATCH] add inline repl tab complete hints

---
 stdlib/REPL/src/LineEdit.jl | 47 +++++++++++++++++++++++++++++++++----
 1 file changed, 42 insertions(+), 5 deletions(-)

diff --git a/stdlib/REPL/src/LineEdit.jl b/stdlib/REPL/src/LineEdit.jl
index ff67e849fcc5a..55cfa87e4b3dc 100644
--- a/stdlib/REPL/src/LineEdit.jl
+++ b/stdlib/REPL/src/LineEdit.jl
@@ -97,6 +97,7 @@ mutable struct PromptState <: ModeState
     p::Prompt
     input_buffer::IOBuffer
     region_active::Symbol # :shift or :mark or :off
+    hint::Union{String,Nothing}
     undo_buffers::Vector{IOBuffer}
     undo_idx::Int
     ias::InputAreaState
@@ -361,7 +362,7 @@ function show_completions(s::PromptState, completions::Vector{String})
     end
 end
 
-# Prompt Completions
+# Prompt Completions & Hints
 function complete_line(s::MIState)
     set_action!(s, :complete_line)
     if complete_line(state(s), s.key_repeats, s.active_module)
@@ -372,6 +373,27 @@ function complete_line(s::MIState)
     end
 end
 
+function check_for_hint(s::MIState)
+    st = state(s)
+    completions, partial, _ = complete_line(st.p.complete, st, s.active_module)::Tuple{Vector{String},String,Bool}
+    if length(completions) == 1
+        st.hint = completions[1][sizeof(partial)+1:end]
+        return refresh_line(s)
+    elseif length(completions) > 1
+        p = common_prefix(completions)
+        if p in completions # i.e. complete `@time` even though `@time_imports` etc. exists
+            st.hint = p[sizeof(partial)+1:end]
+            return refresh_line(s)
+        end
+    end
+    if !isnothing(st.hint)
+        st.hint = "" # don't set to nothing here. That will be done in `maybe_show_hint`
+        return refresh_line(s)
+    else
+        return nothing
+    end
+end
+
 function complete_line(s::PromptState, repeats::Int, mod::Module)
     completions, partial, should_complete = complete_line(s.p.complete, s, mod)::Tuple{Vector{String},String,Bool}
     isempty(completions) && return false
@@ -432,12 +454,27 @@ prompt_string(p::Prompt) = prompt_string(p.prompt)
 prompt_string(s::AbstractString) = s
 prompt_string(f::Function) = Base.invokelatest(f)
 
+function maybe_show_hint(s::PromptState)
+    isa(s.hint, String) || return nothing
+    if isempty(s.hint)
+        print(terminal(s), "\e[0K")
+        s.hint = nothing
+    else
+        Base.printstyled(terminal(s), s.hint, color=:light_black)
+        cmove_left(terminal(s), textwidth(s.hint))
+        s.hint = "" # clear line remainder of line but only once after a hint to allow column movement
+    end
+    return nothing
+end
+
 function refresh_multi_line(s::PromptState; kw...)
     if s.refresh_wait !== nothing
         close(s.refresh_wait)
         s.refresh_wait = nothing
     end
-    refresh_multi_line(terminal(s), s; kw...)
+    r = refresh_multi_line(terminal(s), s; kw...)
+    maybe_show_hint(s)
+    return r
 end
 refresh_multi_line(s::ModeState; kw...) = refresh_multi_line(terminal(s), s; kw...)
 refresh_multi_line(termbuf::TerminalBuffer, s::ModeState; kw...) = refresh_multi_line(termbuf, terminal(s), s; kw...)
@@ -2424,8 +2461,8 @@ AnyDict(
     "\e\n" => "\e\r",
     "^_" => (s::MIState,o...)->edit_undo!(s),
     "\e_" => (s::MIState,o...)->edit_redo!(s),
-    # Simply insert it into the buffer by default
-    "*" => (s::MIState,data,c::StringLike)->(edit_insert(s, c)),
+    # Show hints at what tab complete would do by default
+    "*" => (s::MIState,data,c::StringLike)->(edit_insert(s, c); check_for_hint(s)),
     "^U" => (s::MIState,o...)->edit_kill_line_backwards(s),
     "^K" => (s::MIState,o...)->edit_kill_line_forwards(s),
     "^Y" => (s::MIState,o...)->edit_yank(s),
@@ -2634,7 +2671,7 @@ end
 run_interface(::Prompt) = nothing
 
 init_state(terminal, prompt::Prompt) =
-    PromptState(terminal, prompt, IOBuffer(), :off, IOBuffer[], 1, InputAreaState(1, 1),
+    PromptState(terminal, prompt, IOBuffer(), :off, nothing, IOBuffer[], 1, InputAreaState(1, 1),
                 #=indent(spaces)=# -1, Threads.SpinLock(), 0.0, -Inf, nothing)
 
 function init_state(terminal, m::ModalInterface)