src/libcmd/repl.cc: avoid unneeded reload after :e

If `:edit`ing a store path, don't reload repl afterwards
to avoid losing local variables: store is immutable,
so "editing" a store path is always just viewing it.

Resolves: https://git.lix.systems/lix-project/lix/issues/341
Change-Id: I3747f75ce26e0595e953069c39ddc3ee80699718

doc/manual/change-authors.yml

@@ -57,6 +57,11 @@ ericson:
   display_name: John Ericson
   github: ericson2314
 
+goldstein:
+  display_name: goldstein
+  forgejo: goldstein
+  github: GoldsteinE
+
 horrors:
   display_name: eldritch horrors
   forgejo: pennae

doc/manual/rl-next/repl-edit-store.md

@@ -0,0 +1,11 @@
+---
+synopsis: "`:edit`ing a file in Nix store no longer reloads the repl"
+issues: [fj#341]
+cls: [1620]
+category: Improvements
+credits: [goldstein]
+---
+
+Calling `:edit` from the repl now only reloads if the file being edited was outside of Nix store.
+That means that all the local variables are now preserved across `:edit`s of store paths.
+This is always safe because the store is read-only.

src/libcmd/repl.cc

@@ -652,9 +652,12 @@ ProcessLineResult NixRepl::processLine(std::string line)
         // using runProgram2 to allow editors to display their UI
         runProgram2(RunOptions { .program = editor, .searchPath = true, .args = args }).wait();
 
-        // Reload right after exiting the editor
+        // Reload right after exiting the editor if path is not in store
-        state->resetFileCache();
+        // Store is immutable, so there could be no changes, so there's no need to reload
-        reloadFiles();
+        if (!state->store->isInStore(path.resolveSymlinks().path.abs())) {
+            state->resetFileCache();
+            reloadFiles();
+        }
     }
 
     else if (command == ":t") {

tests/functional/repl.sh

@@ -244,3 +244,30 @@ testReplResponseNoRegex '
   y = { a = 1; };
 }
 '
+
+# Test that editing a store path does not reload...
+echo '{ identity = a: a; }' > repl-test.nix
+repl_test_store="$(nix-store --add repl-test.nix)"
+EDITOR=true testReplResponseNoRegex "
+a = ''test string that we'll grep later''
+:l $repl_test_store
+:e identity
+a
+" "test string that we'll grep later"
+
+# ...even through symlinks
+ln -s "$repl_test_store" repl-test-link.nix
+EDITOR=true testReplResponseNoRegex "
+a = ''test string that we'll grep later''
+:l repl-test-link.nix
+:e identity
+a
+" "test string that we'll grep later"
+
+# Test that editing a local file does reload
+EDITOR=true testReplResponseNoRegex "
+a = ''test string that we'll grep later''
+:l repl-test.nix
+:e identity
+a
+" "undefined variable"