add inline repl tab complete hints

NEWS.md

@@ -48,6 +48,9 @@ Standard library changes
 
 #### REPL
 
+* 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])
+
 #### SuiteSparse
 
 

stdlib/REPL/docs/src/index.md

@@ -312,7 +312,7 @@ Users should refer to `LineEdit.jl` to discover the available actions on key inp
 
 ## Tab completion
 
-In both the Julian and help modes of the REPL, one can enter the first few characters of a function
+In the Julian, pkg and help modes of the REPL, one can enter the first few characters of a function
 or type and then press the tab key to get a list all matches:
 
 ```julia-repl
@@ -334,6 +334,12 @@ julia> mapfold[TAB]
 mapfoldl mapfoldr
 ```
 
+When a single complete tab-complete result is available a hint of the completion will show in a lighter color.
+This can be disabled via `Base.active_repl.options.hint_tab_completes = false`.
+
+!!! compat "Julia 1.11"
+    Tab-complete hinting was added in Julia 1.11
+
 Like other components of the REPL, the search is case-sensitive:
 
 ```julia-repl

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 +373,36 @@ function complete_line(s::MIState)
     end
 end
 
+function check_for_hint(s::MIState)
+    st = state(s)
+    options(st).hint_tab_completes || return nothing
+    completions, partial, should_complete = complete_line(st.p.complete, st, s.active_module)::Tuple{Vector{String},String,Bool}
+    if should_complete
+        if length(completions) == 1
+            hint = only(completions)[sizeof(partial)+1:end]
+            if !isempty(hint) # completion on a complete name returns itself so check that there's something to hint
+                st.hint = hint
+                return refresh_line(s)
+            end
+        elseif length(completions) > 1
+            p = common_prefix(completions)
+            if p in completions # i.e. complete `@time` even though `@time_imports` etc. exists
+                hint = p[sizeof(partial)+1:end]
+                if !isempty(hint)
+                    st.hint = hint
+                    return refresh_line(s)
+                end
+            end
+        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 +463,29 @@ 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
+    # The hint being "" then nothing is used to first clear a previous hint, then skip printing the hint
+    # the clear line cannot be printed each time because it breaks column movement
+    if isempty(s.hint)
+        print(terminal(s), "\e[0K") # clear remainder of line which had a hint
+        s.hint = nothing
+    else
+        Base.printstyled(terminal(s), s.hint, color=:light_black)
+        cmove_left(terminal(s), textwidth(s.hint))
+        s.hint = "" # being "" signals to do one clear line remainder to clear the hint next time if still empty
+    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 +2472,8 @@ 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 +2682,7 @@ 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)

stdlib/REPL/src/options.jl

@@ -27,6 +27,7 @@ mutable struct Options
     auto_indent_time_threshold::Float64
     # refresh after time delay
     auto_refresh_time_delay::Float64
+    hint_tab_completes::Bool
     # default IOContext settings at the REPL
     iocontext::Dict{Symbol,Any}
 end
@@ -47,6 +48,7 @@ Options(;
         auto_indent_bracketed_paste = false,
         auto_indent_time_threshold = 0.005,
         auto_refresh_time_delay = Sys.iswindows() ? 0.05 : 0.0,
+        hint_tab_completes = true,
         iocontext = Dict{Symbol,Any}()) =
             Options(hascolor, extra_keymap, tabwidth,
                     kill_ring_max, region_animation_duration,
@@ -55,6 +57,7 @@ Options(;
                     backspace_align, backspace_adjust, confirm_exit,
                     auto_indent, auto_indent_tmp_off, auto_indent_bracketed_paste,
                     auto_indent_time_threshold, auto_refresh_time_delay,
+                    hint_tab_completes,
                     iocontext)
 
 # for use by REPLs not having an options field

stdlib/REPL/test/repl.jl

@@ -1670,3 +1670,34 @@ fake_repl() do stdin_write, stdout_read, repl
     wait(repltask)
     @test contains(txt, "Some type information was truncated. Use `show(err)` to see complete types.")
 end
+
+fake_repl() do stdin_write, stdout_read, repl
+    repltask = @async begin
+        REPL.run_repl(repl)
+    end
+    write(stdin_write, "reada")
+    s1 = readuntil(stdout_read, "reada") # typed
+    s2 = readuntil(stdout_read, "vailable") # partial hint
+
+    write(stdin_write, "x") # "readax" doesn't tab complete so no hint
+    # we can't use readuntil given this doesn't print, so just wait for the hint state to be reset
+    while LineEdit.state(repl.mistate).hint !== nothing
+        sleep(0.1)
+    end
+    @test LineEdit.state(repl.mistate).hint === nothing
+
+    write(stdin_write, "\b") # only tab complete while typing forward
+    while LineEdit.state(repl.mistate).hint !== nothing
+        sleep(0.1)
+    end
+    @test LineEdit.state(repl.mistate).hint === nothing
+
+    write(stdin_write, "v")
+    s3 = readuntil(stdout_read, "ailable") # partial hint
+
+    write(stdin_write, "\t")
+    s4 = readuntil(stdout_read, "readavailable") # full completion is reprinted
+
+    write(stdin_write, "\x15\x04")
+    Base.wait(repltask)
+end