feat(frontend): Add option to inherit environment

Pantograph/Protocol.lean

@@ -346,6 +346,11 @@ structure FrontendProcess where
   -- One of these two must be supplied: Either supply the file name or the content.
   fileName?: Option String := .none
   file?: Option String := .none
+  -- If set to true, read the header (otherwise discards the header)
+  readHeader : Bool := false
+  -- If set to true, Pantograph's environment will be altered to whatever is
+  -- after the compilation units.
+  inheritEnv : Bool := false
   -- collect tactic invocations
   invocations: Bool := false
   -- collect `sorry`s

Repl.lean

@@ -53,11 +53,10 @@ def frontend_process_inner (args: Protocol.FrontendProcess): MainM (CR Protocol.
     | .none, .some file =>
       pure ("<anonymous>", file)
     | _, _ => return .error <| errorI "arguments" "Exactly one of {fileName, file} must be supplied"
-  let env?: Option Environment ← if args.fileName?.isSome then
+  let env?: Option Environment ← if args.readHeader then
       pure .none
     else do
-      let env ← getEnv
-      pure <| .some env
+      .some <$> getEnv
   let (context, state) ← do Frontend.createContextStateFromFile file fileName env? {}
   let frontendM: Elab.Frontend.FrontendM (List CompilationUnit) :=
     Frontend.mapCompilationSteps λ step => do
@@ -83,7 +82,9 @@ def frontend_process_inner (args: Protocol.FrontendProcess): MainM (CR Protocol.
       messages,
       newConstants
     }
-  let li ← frontendM.run context |>.run' state
+  let (li, state') ← frontendM.run context |>.run state
+  if args.inheritEnv then
+    setEnv state'.commandState.env
   let units ← li.mapM λ step => withEnv step.env do
     let newConstants? := if args.newConstants then
         .some $ step.newConstants.toArray.map λ name => name.toString