fix: make reanalyze work with lib/lsp build artifacts

- Write .sourcedirs.json to lib/lsp/ during full typecheck so the
  analysis layer can discover LSP build artifacts
- Compare .sourcedirs.json mtime (not directory mtime) when choosing
  between lib/bs and lib/lsp — directory mtime only reflects entry
  adds/removes, not content updates
- Pass -absname to bsc in both single-file and batched LSP typecheck
  paths so .cmt files embed absolute source paths for reanalyze
- Use -o and ../../-prefixed source path in single-file typecheck so
  .cmt output lands in the correct build directory

Author: nojaf

analysis/reanalyze/src/Paths.ml

@@ -226,15 +226,13 @@ let newerFile a b =
   | false, false -> a
 
 let readCmtScan () =
-  let bsFile =
-    ["lib"; "bs"; ".sourcedirs.json"]
-    |> List.fold_left Filename.concat runConfig.bsbProjectRoot
-  in
-  let lspFile =
-    ["lib"; "lsp"; ".sourcedirs.json"]
-    |> List.fold_left Filename.concat runConfig.bsbProjectRoot
+  let sourceDirsFile =
+    newerFile
+      (["lib"; "bs"; ".sourcedirs.json"]
+      |> List.fold_left Filename.concat runConfig.bsbProjectRoot)
+      (["lib"; "lsp"; ".sourcedirs.json"]
+      |> List.fold_left Filename.concat runConfig.bsbProjectRoot)
   in
-  let sourceDirsFile = newerFile bsFile lspFile in
   let entries = ref [] in
   let read_entry (json : Ext_json_types.t) =
     match json with

analysis/src/BuildSystem.ml

@@ -43,10 +43,11 @@ let getRuntimeDir rootPath =
 let getLibBs path =
   let bs = path /+ "lib" /+ "bs" in
   let lsp = path /+ "lib" /+ "lsp" in
-  match (Sys.file_exists bs, Sys.file_exists lsp) with
+  let sourcedirs dir = dir /+ ".sourcedirs.json" in
+  match (Sys.file_exists (sourcedirs bs), Sys.file_exists (sourcedirs lsp)) with
   | true, true ->
-    let mtime path = (Unix.stat path).st_mtime in
-    if mtime lsp > mtime bs then Some lsp else Some bs
+    let mtime f = (Unix.stat f).st_mtime in
+    if mtime (sourcedirs lsp) > mtime (sourcedirs bs) then Some lsp else Some bs
   | true, false -> Some bs
   | false, true -> Some lsp
   | false, false -> None

rewatch/src/build/full_typecheck.rs

@@ -1,6 +1,7 @@
 use super::build_types::*;
 use super::compile;
 use crate::build::compiler_info::write_compiler_info;
+use crate::sourcedirs;
 use tracing::{info_span, instrument};
 
 /// Full typecheck: all dirty modules + dependents, typecheck only (no JS).
@@ -54,6 +55,7 @@ pub fn full_typecheck(
         })
     } else {
         write_compiler_info(build_state, OutputTarget::Lsp);
+        sourcedirs::print(build_state, OutputTarget::Lsp);
         Ok(IncrementalBuildResult {
             diagnostics: result.to_diagnostics(),
             modules: params.modules,

rewatch/src/lsp/queue/file_typecheck.rs

@@ -374,7 +374,9 @@ fn typecheck_from_ast(ctx: &FileContext, parent: &tracing::Span) -> TypecheckRes
     )
     .entered();
 
-    let mut args = vec!["-I".to_string(), "src".to_string()];
+    // -absname makes bsc embed absolute paths in .cmt files, which
+    // reanalyze needs to resolve source locations correctly.
+    let mut args = vec!["-absname".to_string(), "-I".to_string(), "src".to_string()];
     args.extend_from_slice(&ctx.file_args.ast_compiler_args);
 
     let output = Command::new(&ctx.file_args.bsc_path)

rewatch/src/lsp/typecheck.rs

@@ -41,9 +41,18 @@ pub fn typecheck_with_args(args: &TypecheckArgs, content: &str) -> Vec<BscDiagno
     // reporting and output prefix derivation.
     let mut full_args = args.compiler_args.clone();
     let source_arg = full_args.pop();
+    // -absname makes bsc embed absolute paths in .cmt files, which
+    // reanalyze needs to resolve source locations correctly.
+    full_args.push("-absname".into());
     full_args.push("-bs-read-stdin".into());
-    if let Some(arg) = source_arg {
-        full_args.push(arg);
+    if let Some(source) = source_arg {
+        // bsc runs from lib/lsp/ — use -o to keep .cmt output in the build
+        // dir, while the ../../-prefixed source path lets -absname resolve
+        // the correct absolute path for embedding inside the .cmt.
+        full_args.push("-o".into());
+        full_args.push(source.clone());
+        let prefixed = Path::new("../..").join(&source).to_string_lossy().into_owned();
+        full_args.push(prefixed);
     }
 
     let mut child = match Command::new(&args.bsc_path)