Spell files below source dir "." without a leading "./"

changes/root-source-dir-rebuild.fix.md

@@ -0,0 +1,2 @@
+- Stop `rescript` from rebuilding the modules of a `"."` or `"./src"` source
+  dir, and their dependents, on every build when nothing changed.

rewatch-ocaml/build_artifacts.ml

@@ -12,10 +12,13 @@ let relative_output_directory path (spec : Config.package_spec) =
 
 let generated_js_path (config : Config.t) path (spec : Config.package_spec) =
   let output_dir = relative_output_directory path spec in
+  (* The output of a module of the package root is "A.js" or "lib/es6/A.js",
+     as the output inventory spells it, not "./A.js" or "lib/es6/./A.js". *)
   Filename.concat config.root
-    (Filename.concat output_dir
-       (Filename.remove_extension (Filename.basename path)
-       ^ Config.package_spec_suffix config spec))
+    (Source.without_current_dir_segments
+       (Filename.concat output_dir
+          (Filename.remove_extension (Filename.basename path)
+          ^ Config.package_spec_suffix config spec)))
 
 let published_ast_path ~ocaml_dir source =
   Filename.concat ocaml_dir (Filename.basename (Source.ast_path source))

rewatch-ocaml/source.ml

@@ -81,6 +81,22 @@ let interface_mismatch_error implementation interface =
         different path names or different cases: `%s` vs `%s`"
        implementation interface)
 
+(* [path] without its "." segments, so a file found below source dir "." or
+   "./src" has the path bsc records for it, "A.res" or "src/A.res". Cleanup and
+   freshness match modules to their ASTs and outputs by these paths: a
+   "./A.res" matched no AST, and a "./ui/U.js" in the inventory of "." matched
+   no module's output, so each build removed them and rebuilt the module. *)
+let rec without_current_dir_segments path =
+  let directory = Filename.dirname path in
+  let base = Filename.basename path in
+  if directory = path || path = Filename.current_dir_name then path
+  else if base = Filename.current_dir_name then
+    without_current_dir_segments directory
+  else
+    match without_current_dir_segments directory with
+    | directory when directory = Filename.current_dir_name -> base
+    | directory -> Filename.concat directory base
+
 (* A package source tree has three consumers with deliberately different
    recursion rules. Compilation follows directory links and honors source
    activation/subdirs; cleanup inventories every real descendant but treats
@@ -134,7 +150,11 @@ let scan_source ~root (source : Config.source) ~discover_modules ~on_missing
           | Some kind ->
             candidates :=
               {
-                file = {path = relative_path; modified = metadata.Unix.st_mtime};
+                file =
+                  {
+                    path = without_current_dir_segments relative_path;
+                    modified = metadata.Unix.st_mtime;
+                  };
                 kind;
                 is_dev = source.is_dev;
               }
@@ -143,7 +163,9 @@ let scan_source ~root (source : Config.source) ~discover_modules ~on_missing
       List.iter
         (fun name ->
           let relative_path = Filename.concat relative name in
-          let absolute_path = Filename.concat root relative_path in
+          let absolute_path =
+            Filename.concat root (without_current_dir_segments relative_path)
+          in
           match Unix.lstat absolute_path with
           | metadata -> (
             match metadata.Unix.st_kind with

rewatch-ocaml/source.mli

@@ -23,6 +23,10 @@ type source_kind = Implementation | Interface
 
 val source_kind : string -> source_kind option
 val module_name : string -> string
+
+val without_current_dir_segments : string -> string
+(** [path] without its "." segments: "./src/./A.res" is "src/A.res". *)
+
 val namespace_members : entry:string option -> module_ list -> module_ list
 
 val duplicate_error :

rewatch/tests/compile/23-root-source-dir-rebuild.sh

@@ -0,0 +1,57 @@
+#!/bin/bash
+
+cd $(dirname $0)
+source "../utils.sh"
+
+bold "Test: Modules of source dir \".\" are not rebuilt when nothing changed"
+
+fixtures=$(mktemp -d 2>/dev/null || mktemp -d -t rewatch-root-source-dir)
+trap "rm -rf '$fixtures'" EXIT
+
+# "." spells its modules "./Root.res" unless the build system drops the
+# segment, while bsc records "Root.res" in the AST and the output inventory
+# finds "Root.mjs" or "lib/es6/Root.mjs". A mismatch makes every build clean
+# those artifacts.
+check_layout() {
+  local name=$1 in_source=$2 root_output=$3 ui_output=$4
+  local fixture="$fixtures/$name"
+  mkdir -p "$fixture/ui"
+
+  cat > "$fixture/rescript.json" <<JSON
+{
+  "name": "rewatch-root-source-dir-$name",
+  "sources": [{ "dir": "." }, { "dir": "ui" }],
+  "package-specs": { "module": "esmodule", "in-source": $in_source },
+  "suffix": ".mjs"
+}
+JSON
+
+  printf 'let value = 1\n' > "$fixture/Root.res"
+  printf 'let value = Root.value + 1\n' > "$fixture/ui/Component.res"
+
+  if ! compiler_output=$(cd "$fixture" && "$REWATCH_EXECUTABLE" build 2>&1); then
+    error "Initial $name fixture build failed"
+    printf "%s\n" "$compiler_output" >&2
+    return 1
+  fi
+
+  # Several unchanged builds, since a removed output only shows on the next one.
+  for attempt in 1 2 3; do
+    compiler_output=$(cd "$fixture" && "$REWATCH_EXECUTABLE" build 2>&1)
+    if ! printf '%s\n' "$compiler_output" | grep -q "Compiled 0 modules"; then
+      error "Unchanged $name build $attempt recompiled modules"
+      printf "%s\n" "$compiler_output" >&2
+      return 1
+    fi
+  done
+
+  if [ ! -f "$fixture/$root_output" ] || [ ! -f "$fixture/$ui_output" ]; then
+    error "Unchanged $name builds removed generated outputs"
+    return 1
+  fi
+}
+
+check_layout in-source true Root.mjs ui/Component.mjs || exit 1
+check_layout out-of-source false lib/es6/Root.mjs lib/es6/ui/Component.mjs || exit 1
+
+success "Modules of source dir \".\" are not rebuilt when nothing changed"

rewatch/tests/suite.sh

@@ -88,6 +88,7 @@ fi
 ./compile/20-schedule-independent-modules-after-error.sh &&
 ./compile/21-rebuild-dependency-for-package-specs.sh &&
 ./compile/22-qualified-own-namespace-dependency.sh &&
+./compile/23-root-source-dir-rebuild.sh &&
 ./compile/14-no-testrepo-changes.sh &&
 ./compile/15-no-new-files.sh &&
 ./compile/16-snapshots-unchanged.sh &&