DCE: Remove WriteDeadAnnotations feature

The `-write` flag that auto-inserted `@dead` annotations into source files
was removed as it added significant complexity for a rarely-used feature.

## Deleted

- `WriteDeadAnnotations.ml` (156 lines)
- `Common.Cli.write` ref
- `DceConfig.cli.write` field
- `type line` and `type lineAnnotation` in Common.ml
- `shouldWriteLineAnnotation` and `lineAnnotation` fields in DeadWarning
- `-write` CLI argument
- `~config` parameter from `logAdditionalInfo` (now unused)

## Simplified

- `emitWarning` no longer computes line annotations
- `logAdditionalInfo` no longer needs config parameter
- DeadWarning type now just has: deadWarning, path, message

## Rationale

The feature:
- Added file I/O during analysis (violated pure analysis principles)
- Maintained global state (currentFile, currentFileLines refs)
- Required threading lineAnnotation through warning system
- Was rarely used (most users want to delete dead code, not annotate it)

Users who want to suppress warnings can still manually add `@dead` annotations.

Author: cristianoc

analysis/reanalyze/DEADCODE_REFACTOR_PLAN.md

@@ -100,7 +100,7 @@ you can swap one file's data without affecting others.
 **Problem**: Analysis functions directly call:
 - `Log_.warning` - logging
 - `EmitJson` - JSON output  
-- `WriteDeadAnnotations` - file I/O
+- ~~`WriteDeadAnnotations` - file I/O~~ (removed - added complexity with little value)
 - Direct mutation of result data structures
 
 **Impact**: Can't get analysis results as data. Can't test without capturing I/O. Can't reuse analysis logic for different output formats.
@@ -440,19 +440,14 @@ This enables parallelization, caching, and incremental recomputation.
 
 **Estimated effort**: Medium (many logging call sites, but mechanical)
 
-### Task 9: Separate annotation computation from file writing (P5)
+### Task 9: ~~Separate annotation computation from file writing (P5)~~ REMOVED
 
-**Value**: Can compute what to write without actually writing. Testable.
+**Status**: Removed ✅ - `WriteDeadAnnotations` feature was deleted entirely.
 
-**Changes**:
-- [ ] `WriteDeadAnnotations`: Split into pure `compute_annotations` and impure `write_to_files`
-- [ ] Pure function takes deadness results, returns `(filepath * line_annotation list) list`
-- [ ] Impure function takes that list and does file I/O
-- [ ] Remove file I/O from analysis path
-
-**Test**: Compute annotations, verify correct without touching filesystem.
-
-**Estimated effort**: Small (single module)
+The `-write` flag that auto-inserted `@dead` annotations into source files was removed
+as it added significant complexity (global state, file I/O during analysis, extra types)
+for a rarely-used feature. Users who want to suppress dead code warnings can manually
+add `@dead` annotations.
 
 ### Task 10: Verify zero `DceConfig.current()` calls in analysis code
 

analysis/reanalyze/src/CollectAnnotations.ml

@@ -14,8 +14,7 @@ let processAttributes ~state ~config ~doGenType ~name ~pos attributes =
     doGenType
     && getPayloadFun Annotation.tagIsOneOfTheGenTypeAnnotations <> None
   then FileAnnotations.annotate_gentype state pos;
-  if getPayload WriteDeadAnnotations.deadAnnotation <> None then
-    FileAnnotations.annotate_dead state pos;
+  if getPayload "dead" <> None then FileAnnotations.annotate_dead state pos;
   let nameIsInLiveNamesOrPaths () =
     config.DceConfig.cli.live_names |> List.mem name
     ||

analysis/reanalyze/src/Common.ml

@@ -17,7 +17,6 @@ module Cli = struct
 
   let experimental = ref false
   let json = ref false
-  let write = ref false
 
   (* names to be considered live values *)
   let liveNames = ref ([] : string list)
@@ -174,8 +173,6 @@ type decl = {
   mutable report: bool;
 }
 
-type line = {mutable declarations: decl list; original: string}
-
 module ExnSet = Set.Make (Exn)
 
 type missingThrowInfo = {
@@ -202,21 +199,13 @@ type deadWarning =
   | WarningDeadValueWithSideEffects
   | IncorrectDeadAnnotation
 
-type lineAnnotation = (decl * line) option
-
 type description =
   | Circular of {message: string}
   | ExceptionAnalysis of {message: string}
   | ExceptionAnalysisMissing of missingThrowInfo
   | DeadModule of {message: string}
   | DeadOptional of {deadOptional: deadOptional; message: string}
-  | DeadWarning of {
-      deadWarning: deadWarning;
-      path: string;
-      message: string;
-      shouldWriteLineAnnotation: bool;
-      lineAnnotation: lineAnnotation;
-    }
+  | DeadWarning of {deadWarning: deadWarning; path: string; message: string}
   | Termination of {termination: termination; message: string}
 
 type issue = {

analysis/reanalyze/src/DceConfig.ml

@@ -7,7 +7,6 @@ type cli_config = {
   debug: bool;
   ci: bool;
   json: bool;
-  write: bool;
   live_names: string list;
   live_paths: string list;
   exclude_paths: string list;
@@ -25,7 +24,6 @@ let current () =
       debug = !Common.Cli.debug;
       ci = !Common.Cli.ci;
       json = !Common.Cli.json;
-      write = !Common.Cli.write;
       live_names = !Common.Cli.liveNames;
       live_paths = !Common.Cli.livePaths;
       exclude_paths = !Common.Cli.excludePaths;

analysis/reanalyze/src/DeadCommon.ml

@@ -78,7 +78,9 @@ end
 let declGetLoc decl =
   let loc_start =
     let offset =
-      WriteDeadAnnotations.offsetOfPosAdjustment decl.posAdjustment
+      match decl.posAdjustment with
+      | FirstVariant | Nothing -> 0
+      | OtherVariant -> 2
     in
     let cnumWithOffset = decl.posStart.pos_cnum + offset in
     if cnumWithOffset < decl.posEnd.pos_cnum then
@@ -159,33 +161,11 @@ let addValueDeclaration ~config ~decls ~file ?(isToplevel = true)
 
 let emitWarning ~config ~decl ~message deadWarning =
   let loc = decl |> declGetLoc in
-  let isToplevelValueWithSideEffects decl =
-    match decl.declKind with
-    | Value {isToplevel; sideEffects} -> isToplevel && sideEffects
-    | _ -> false
-  in
-  let shouldWriteLineAnnotation =
-    (not (isToplevelValueWithSideEffects decl))
-    && Suppress.filter decl.pos
-    && deadWarning <> IncorrectDeadAnnotation
-  in
-  let lineAnnotation =
-    if shouldWriteLineAnnotation then
-      WriteDeadAnnotations.addLineAnnotation ~config ~decl
-    else None
-  in
   decl.path
   |> Path.toModuleName ~isType:(decl.declKind |> DeclKind.isType)
   |> DeadModules.checkModuleDead ~config ~fileName:decl.pos.pos_fname;
   Log_.warning ~loc
-    (DeadWarning
-       {
-         deadWarning;
-         path = Path.withoutHead decl.path;
-         message;
-         lineAnnotation;
-         shouldWriteLineAnnotation;
-       })
+    (DeadWarning {deadWarning; path = Path.withoutHead decl.path; message})
 
 module Decl = struct
   let isValue decl =

analysis/reanalyze/src/DeadType.ml

@@ -119,8 +119,12 @@ let addDeclaration ~config ~decls ~file ~(typeId : Ident.t)
         in
         let posAdjustment =
           (* In Res the variant loc can include the | and spaces after it *)
-          if WriteDeadAnnotations.posLanguage cd_loc.loc_start = Res then
-            if i = 0 then FirstVariant else OtherVariant
+          let isRes =
+            let fname = cd_loc.loc_start.pos_fname in
+            Filename.check_suffix fname ".res"
+            || Filename.check_suffix fname ".resi"
+          in
+          if isRes then if i = 0 then FirstVariant else OtherVariant
           else Nothing
         in
         Ident.name cd_id |> Name.create

analysis/reanalyze/src/Log_.ml

@@ -107,12 +107,8 @@ let missingRaiseInfoToText {missingAnnotations; locFull} =
       ~text:(Format.asprintf "@throws(%s)\\n" missingTxt)
   else ""
 
-let logAdditionalInfo ~config ~(description : description) =
+let logAdditionalInfo ~(description : description) =
   match description with
-  | DeadWarning {lineAnnotation; shouldWriteLineAnnotation} ->
-    if shouldWriteLineAnnotation then
-      WriteDeadAnnotations.lineAnnotationToString ~config lineAnnotation
-    else ""
   | ExceptionAnalysisMissing missingRaiseInfo ->
     missingRaiseInfoToText missingRaiseInfo
   | _ -> ""
@@ -187,7 +183,7 @@ let logIssue ~config ~(issue : issue) =
           ~range:(startLine, startCharacter, endLine, endCharacter)
           ~message)
       ()
-      (logAdditionalInfo ~config ~description:issue.description)
+      (logAdditionalInfo ~description:issue.description)
       (if config.DceConfig.cli.json then EmitJson.emitClose () else "")
   else
     let color =
@@ -197,7 +193,7 @@ let logIssue ~config ~(issue : issue) =
     in
     asprintf "@.  %a@.  %a@.  %s%s@." color issue.name Loc.print issue.loc
       (descriptionToMessage issue.description)
-      (logAdditionalInfo ~config ~description:issue.description)
+      (logAdditionalInfo ~description:issue.description)
 
 module Stats = struct
   let issues = ref []

analysis/reanalyze/src/Reanalyze.ml

@@ -153,8 +153,7 @@ let runAnalysis ~dce_config ~cmtRoot =
     let refs = References.freeze_builder refs_builder in
     let file_deps = FileDeps.freeze_builder file_deps_builder in
     DeadCommon.reportDead ~annotations ~decls ~refs ~file_deps
-      ~config:dce_config ~checkOptionalArg:DeadOptionalArgs.check;
-    WriteDeadAnnotations.write ~config:dce_config);
+      ~config:dce_config ~checkOptionalArg:DeadOptionalArgs.check);
   if dce_config.DceConfig.run.exception_ then
     Exception.Checks.doChecks ~config:dce_config;
   if dce_config.DceConfig.run.termination && dce_config.DceConfig.cli.debug then
@@ -271,9 +270,6 @@ let cli () =
          specified)" );
       ("-version", Unit versionAndExit, "Show version information and exit");
       ("--version", Unit versionAndExit, "Show version information and exit");
-      ( "-write",
-        Set Common.Cli.write,
-        "Write @dead annotations directly in the source files" );
     ]
   in
   Arg.parse speclist print_endline usage;