fix JuliaLang#27546 by using jl_set_global instead of eval to set Main.ans (JuliaLang#27562)

Author: jrevels

base/client.jl

@@ -121,7 +121,7 @@ function eval_user_input(@nospecialize(ast), show_value::Bool)
             else
                 ast = Meta.lower(Main, ast)
                 value = Core.eval(Main, ast)
-                Core.eval(Main, Expr(:body, Expr(:(=), :ans, QuoteNode(value)), Expr(:return, nothing)))
+                ccall(:jl_set_global, Cvoid, (Any, Any, Any), Main, :ans, value)
                 if !(value === nothing) && show_value
                     if have_color
                         print(answer_color())

stdlib/REPL/src/REPL.jl

@@ -85,7 +85,7 @@ function eval_user_input(@nospecialize(ast), backend::REPLBackend)
                 value = Core.eval(Main, ast)
                 backend.in_eval = false
                 # note: value wrapped carefully here to ensure it doesn't get passed through expand
-                Core.eval(Main, Expr(:body, Expr(:(=), :ans, QuoteNode(value)), Expr(:return, nothing)))
+                ccall(:jl_set_global, Cvoid, (Any, Any, Any), Main, :ans, value)
                 put!(backend.response_channel, (value, nothing))
             end
             break

stdlib/REPL/test/repl.jl

@@ -961,3 +961,19 @@ for (line, expr) in Pair[
     buf = IOBuffer()
     @test Base.eval(REPL._helpmode(buf, line)) isa Union{Markdown.MD,Nothing}
 end
+
+# PR #27562
+fake_repl() do stdin_write, stdout_read, repl
+    repltask = @async begin
+        REPL.run_repl(repl)
+    end
+    write(stdin_write, "Expr(:call, GlobalRef(Base.Math, :float), Core.SlotNumber(1))\n")
+    readline(stdout_read)
+    @test readline(stdout_read) == "\e[0m:((Base.Math.float)(_1))"
+    write(stdin_write, "ans\n")
+    readline(stdout_read)
+    readline(stdout_read)
+    @test readline(stdout_read) == "\e[0m:((Base.Math.float)(_1))"
+    write(stdin_write, '\x04')
+    Base._wait(repltask)
+end