[REPL] Handle empty completion, keywords better (#59045)

When the context is empty, (like "<TAB><TAB>"), return only names local
to the module (fixes #58931).

If the cursor is on something that "looks like" an identifier, like a
boolean or one of the keywords, treat it as if it was one for completion
purposes. Typing a keyword and hitting tab no longer returns the
completions for the empty input (fixes #58309, #58832).

Author: xal-0

stdlib/REPL/src/REPLCompletions.jl

@@ -186,7 +186,7 @@ function complete_symbol!(suggestions::Vector{Completion},
                           complete_modules_only::Bool=false,
                           shift::Bool=false)
     local mod, t, val
-    complete_internal_only = false
+    complete_internal_only = isempty(name)
     if prefix !== nothing
         res = repl_eval_ex(prefix, context_module)
         res === nothing && return Completion[]
@@ -1095,26 +1095,27 @@ function completions(string::String, pos::Int, context_module::Module=Main, shif
 
     # Symbol completion
     # TODO: Should completions replace the identifier at the cursor?
+    looks_like_ident = Base.isidentifier(@view string[intersect(char_range(cur), 1:pos)])
     if cur.parent !== nothing && kind(cur.parent) == K"var"
         # Replace the entire var"foo", but search using only "foo".
         r = intersect(char_range(cur.parent), 1:pos)
         r2 = char_range(children_nt(cur.parent)[1])
         s = string[intersect(r2, 1:pos)]
-    elseif kind(cur) in KSet"Identifier @"
-        r = intersect(char_range(cur), 1:pos)
-        s = string[r]
     elseif kind(cur) == K"MacroName"
         # Include the `@`
         r = intersect(prevind(string, cur.position):char_last(cur), 1:pos)
         s = string[r]
+    elseif looks_like_ident || kind(cur) in KSet"Bool Identifier @"
+        r = intersect(char_range(cur), 1:pos)
+        s = string[r]
     else
         r = nextind(string, pos):pos
         s = ""
     end
 
     complete_modules_only = false
     prefix = node_prefix(cur, context_module)
-    comp_keywords = prefix === nothing
+    comp_keywords = prefix === nothing && !isempty(s)
 
     # Complete loadable module names:
     #   import Mod TAB

stdlib/REPL/test/replcompletions.jl

@@ -2720,3 +2720,25 @@ let s = "foo58296(findfi"
     @test "findfirst" in c
     @test r == 10:15
 end
+
+# #58931 - only show local names when completing the empty string
+let s = ""
+    c, r = test_complete_foo(s)
+    @test "test" in c
+    @test !("rand" in c)
+end
+
+# #58309, #58832 - don't show every name when completing after a full keyword
+let s = "true"     # bool is a little different (Base.isidentifier special case)
+    c, r = test_complete(s)
+    @test "trues" in c
+    @test "true" in c
+    @test !("rand" in c)
+end
+
+let s = "for"
+    c, r = test_complete(s)
+    @test "for" in c
+    @test "foreach" in c
+    @test !("rand" in c)
+end