REPL: offer to try to install package if not found

stdlib/REPL/src/REPL.jl

@@ -334,6 +334,26 @@ end
 outstream(r::BasicREPL) = r.terminal
 hascolor(r::BasicREPL) = hascolor(r.terminal)
 
+function try_pkg_add(mod::Symbol)
+    resp = try
+        Base.prompt(" \033[32m\033[1m└\033[22m\033[0m Package $(repr(String(mod))) not found, with active project $(repr(Base.active_project()))
+   Try adding $(repr(String(mod))) to the active environment? (y/n)",
+        default = "n")
+    catch err
+        if err isa InterruptException
+            println()
+            return false
+        end
+    end
+    if lowercase(resp) in ["y", "yes"]
+        let Pkg = Base.require(Base.PkgId(Base.UUID((0x44cfe95a_1eb2_52ea,0xb672_e2afdf69b78f)), "Pkg"))
+            Pkg.add(string(mod))
+            return true
+        end
+    end
+    return false
+end
+
 function run_frontend(repl::BasicREPL, backend::REPLBackendRef)
     d = REPLDisplay(repl)
     dopushdisplay = !in(d,Base.Multimedia.displays)
@@ -776,7 +796,14 @@ backend(r::AbstractREPL) = r.backendref
 
 function eval_with_backend(ast, backend::REPLBackendRef)
     put!(backend.repl_channel, (ast, 1))
-    return take!(backend.response_channel) # (val, iserr)
+    resp = take!(backend.response_channel) # (val, iserr)
+    if last(resp)
+        err = first(first(first(resp)))
+        if err isa ModuleNotFoundError
+            try_pkg_add(err.mod) && return Pair{Any, Bool}(nothing, false)
+        end
+    end
+    return resp
 end
 
 function respond(f, repl, main; pass_empty::Bool = false, suppress_on_semicolon::Bool = true)