Fix warning loss during incremental builds in watch mode (#8216)

nojaf · web-flow · commit 3fe9059c3581 · 2026-01-23T13:39:50.000Z
* Fix warning loss during incremental builds in watch mode

* Add changelog

* Update lock file

* Remove sleep

* Update existing snapshots with added warning

* Rename field
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -20,7 +20,7 @@
 - Remove the deprecated module system names `es6` and `es6-global` (superseded by `esmodule`). https://github.com/rescript-lang/rescript/pull/8205
 - Default to module system `esmodule`. https://github.com/rescript-lang/rescript/pull/8213
 - Remove `external-stdlib` configuration option from `rescript.json`. This option was rarely used and is no longer supported.
-- Remove the deprecated uncurried `(. args) => ...` function syntax. https://github.com/rescript-lang/rescript/pull/8211 
+- Remove the deprecated uncurried `(. args) => ...` function syntax. https://github.com/rescript-lang/rescript/pull/8211
 - `js-post-build` now passes the correct output file path based on `in-source` configuration: when `in-source: true`, the path next to the source file is passed; when `in-source: false`, the path in the `lib/<module>/` directory is passed. Additionally, stdout and stderr from the post-build command are now logged. https://github.com/rescript-lang/rescript/pull/8190
 - `js-post-build` command now runs in the directory containing the `rescript.json` where it is defined, instead of the unpredictable build invocation directory. This provides consistent behavior in monorepos. https://github.com/rescript-lang/rescript/pull/8195
 - Remove support for deprecated `bs-dependencies`, `bs-dev-dependencies`, and `bsc-flags` configuration options. Use `dependencies`, `dev-dependencies`, and `compiler-flags` instead. https://github.com/rescript-lang/rescript/pull/8196
@@ -40,6 +40,7 @@
 - Add duplicate package detection to rewatch. https://github.com/rescript-lang/rescript/pull/8180
 - Rewatch: do not warn about "reanalyze" config field. https://github.com/rescript-lang/rescript/pull/8181
 - Fix error when importing CommonJS runtime modules with `require()`. https://github.com/rescript-lang/rescript/pull/8194
+- Rewatch: fix warnings from non-recompiled modules being lost during incremental builds in watch mode. https://github.com/rescript-lang/rescript/pull/8216
 
 #### :memo: Documentation
 
diff --git a/rewatch/src/build/build_types.rs b/rewatch/src/build/build_types.rs
@@ -27,6 +27,10 @@ pub struct Interface {
     pub compile_state: CompileState,
     pub last_modified: SystemTime,
     pub parse_dirty: bool,
+    /// Compiler warning output (from bsc stderr) stored for re-emission
+    /// during incremental builds when this module is not recompiled.
+    /// Written to `.compiler.log` on each build cycle.
+    pub compile_warnings: Option<String>,
 }
 
 #[derive(Debug, Clone, PartialEq)]
@@ -36,6 +40,10 @@ pub struct Implementation {
     pub compile_state: CompileState,
     pub last_modified: SystemTime,
     pub parse_dirty: bool,
+    /// Compiler warning output (from bsc stderr) stored for re-emission
+    /// during incremental builds when this module is not recompiled.
+    /// Written to `.compiler.log` on each build cycle.
+    pub compile_warnings: Option<String>,
 }
 
 #[derive(Debug, Clone, PartialEq)]
diff --git a/rewatch/src/build/compile.rs b/rewatch/src/build/compile.rs
@@ -327,15 +327,19 @@ pub fn compile(
                     }
                     SourceType::SourceFile(ref mut source_file) => match result {
                         Ok(Some(err)) => {
+                            let warning_text = err.to_string();
                             source_file.implementation.compile_state = CompileState::Warning;
-                            (Some(err.to_string()), None)
+                            source_file.implementation.compile_warnings = Some(warning_text.clone());
+                            (Some(warning_text), None)
                         }
                         Ok(None) => {
                             source_file.implementation.compile_state = CompileState::Success;
+                            source_file.implementation.compile_warnings = None;
                             (None, None)
                         }
                         Err(err) => {
                             source_file.implementation.compile_state = CompileState::Error;
+                            source_file.implementation.compile_warnings = None;
                             (None, Some(err.to_string()))
                         }
                     },
@@ -345,17 +349,22 @@ pub fn compile(
                     if let SourceType::SourceFile(ref mut source_file) = module.source_type {
                         match interface_result {
                             Some(Ok(Some(err))) => {
+                                let warning_text = err.to_string();
                                 source_file.interface.as_mut().unwrap().compile_state = CompileState::Warning;
-                                (Some(err.to_string()), None)
+                                source_file.interface.as_mut().unwrap().compile_warnings =
+                                    Some(warning_text.clone());
+                                (Some(warning_text), None)
                             }
                             Some(Ok(None)) => {
                                 if let Some(interface) = source_file.interface.as_mut() {
                                     interface.compile_state = CompileState::Success;
+                                    interface.compile_warnings = None;
                                 }
                                 (None, None)
                             }
                             Some(Err(err)) => {
                                 source_file.interface.as_mut().unwrap().compile_state = CompileState::Error;
+                                source_file.interface.as_mut().unwrap().compile_warnings = None;
                                 (None, Some(err.to_string()))
                             }
                             _ => (None, None),
@@ -434,6 +443,32 @@ pub fn compile(
         };
     }
 
+    // Collect warnings from modules that were not recompiled in this build
+    // but still have stored warnings from a previous compilation.
+    // This ensures warnings are not lost during incremental builds in watch mode.
+    for (module_name, module) in build_state.modules.iter() {
+        if compile_universe.contains(module_name) {
+            continue;
+        }
+        if let SourceType::SourceFile(ref source_file) = module.source_type {
+            let package = build_state.get_package(&module.package_name);
+            if let Some(ref warning) = source_file.implementation.compile_warnings {
+                if let Some(package) = package {
+                    logs::append(package, warning);
+                }
+                compile_warnings.push_str(warning);
+            }
+            if let Some(ref interface) = source_file.interface
+                && let Some(ref warning) = interface.compile_warnings
+            {
+                if let Some(package) = package {
+                    logs::append(package, warning);
+                }
+                compile_warnings.push_str(warning);
+            }
+        }
+    }
+
     Ok((compile_errors, compile_warnings, num_compiled_modules))
 }
 
diff --git a/rewatch/src/build/packages.rs b/rewatch/src/build/packages.rs
@@ -800,6 +800,7 @@ pub fn parse_packages(build_state: &mut BuildState) -> Result<()> {
                                         compile_state: CompileState::Pending,
                                         last_modified: metadata.modified,
                                         parse_dirty: true,
+                                        compile_warnings: None,
                                     },
                                     interface: None,
                                 }),
@@ -871,6 +872,7 @@ pub fn parse_packages(build_state: &mut BuildState) -> Result<()> {
                                             compile_state: CompileState::Pending,
                                             last_modified: metadata.modified,
                                             parse_dirty: true,
+                                            compile_warnings: None,
                                         });
                                     }
                                 })
@@ -884,13 +886,15 @@ pub fn parse_packages(build_state: &mut BuildState) -> Result<()> {
                                             compile_state: CompileState::Pending,
                                             last_modified: metadata.modified,
                                             parse_dirty: true,
+                                            compile_warnings: None,
                                         },
                                         interface: Some(Interface {
                                             path: file.to_owned(),
                                             parse_state: ParseState::Pending,
                                             compile_state: CompileState::Pending,
                                             last_modified: metadata.modified,
                                             parse_dirty: true,
+                                            compile_warnings: None,
                                         }),
                                     }),
                                     deps: AHashSet::new(),
diff --git a/rewatch/testrepo/package.json b/rewatch/testrepo/package.json
@@ -16,7 +16,8 @@
       "packages/pure-dev",
       "packages/with-ppx",
       "packages/nohoist",
-      "packages/standalone"
+      "packages/standalone",
+      "packages/watch-warnings"
     ],
     "nohoist": [
       "rescript-bun"
diff --git a/rewatch/testrepo/packages/watch-warnings/package.json b/rewatch/testrepo/packages/watch-warnings/package.json
@@ -0,0 +1,4 @@
+{
+  "name": "@testrepo/watch-warnings",
+  "version": "0.0.1"
+}
diff --git a/rewatch/testrepo/packages/watch-warnings/rescript.json b/rewatch/testrepo/packages/watch-warnings/rescript.json
@@ -0,0 +1,12 @@
+{
+  "name": "@testrepo/watch-warnings",
+  "sources": {
+    "dir": "src",
+    "subdirs": true
+  },
+  "package-specs": {
+    "module": "commonjs",
+    "in-source": true
+  },
+  "suffix": ".bs.js"
+}
diff --git a/rewatch/testrepo/packages/watch-warnings/src/B.mjs b/rewatch/testrepo/packages/watch-warnings/src/B.mjs
@@ -0,0 +1,11 @@
+// Generated by ReScript, PLEASE EDIT WITH CARE
+
+
+function world() {
+  console.log("world");
+}
+
+export {
+  world,
+}
+/* No side effect */
diff --git a/rewatch/testrepo/packages/watch-warnings/src/B.res b/rewatch/testrepo/packages/watch-warnings/src/B.res
@@ -0,0 +1 @@
+let world = () => Console.log("world")
diff --git a/rewatch/testrepo/packages/watch-warnings/src/ModuleA.mjs b/rewatch/testrepo/packages/watch-warnings/src/ModuleA.mjs
@@ -0,0 +1,11 @@
+// Generated by ReScript, PLEASE EDIT WITH CARE
+
+
+function hello() {
+  console.log("hello");
+}
+
+export {
+  hello,
+}
+/* No side effect */
diff --git a/rewatch/testrepo/packages/watch-warnings/src/ModuleA.res b/rewatch/testrepo/packages/watch-warnings/src/ModuleA.res
@@ -0,0 +1,3 @@
+let unusedValue = 42
+
+let hello = () => Console.log("hello")
diff --git a/rewatch/testrepo/packages/watch-warnings/src/ModuleA.resi b/rewatch/testrepo/packages/watch-warnings/src/ModuleA.resi
@@ -0,0 +1 @@
+let hello: unit => unit
diff --git a/rewatch/testrepo/rescript.json b/rewatch/testrepo/rescript.json
@@ -25,9 +25,8 @@
     "@testrepo/file-casing",
     "@testrepo/file-casing-no-namespace",
     "@testrepo/with-ppx",
-    "@testrepo/nohoist"
+    "@testrepo/nohoist",
+    "@testrepo/watch-warnings"
   ],
-  "dev-dependencies": [
-    "@testrepo/pure-dev"
-  ]
+  "dev-dependencies": ["@testrepo/pure-dev"]
 }
diff --git a/rewatch/testrepo/yarn.lock b/rewatch/testrepo/yarn.lock
@@ -159,6 +159,12 @@ __metadata:
   languageName: unknown
   linkType: soft
 
+"@testrepo/watch-warnings@workspace:packages/watch-warnings":
+  version: 0.0.0-use.local
+  resolution: "@testrepo/watch-warnings@workspace:packages/watch-warnings"
+  languageName: unknown
+  linkType: soft
+
 "@testrepo/with-dev-deps@workspace:packages/with-dev-deps":
   version: 0.0.0-use.local
   resolution: "@testrepo/with-dev-deps@workspace:packages/with-dev-deps"
diff --git a/rewatch/tests/snapshots/clean-rebuild.txt b/rewatch/tests/snapshots/clean-rebuild.txt
@@ -1,6 +1,17 @@
 Cleaned 0/0
-Parsed 428 source files
-Compiled 428 modules
+Parsed 430 source files
+Compiled 430 modules
+
+  [1;33mWarning number 32[0m
+  [36m/packages/watch-warnings/src/ModuleA.res[0m:[2m1:5-15[0m
+
+  [1;33m1[0m [2m│[0m let [1;33munusedValue[0m = 42
+  2 [2m│[0m 
+  3 [2m│[0m let hello = () => Console.log("hello")
+
+  unused value unusedValue.
+
+
 
 The field 'ignored-dirs' found in the package config of '@testrepo/deprecated-config' is not supported by ReScript 12's new build system.
 
diff --git a/rewatch/tests/snapshots/dependency-cycle.txt b/rewatch/tests/snapshots/dependency-cycle.txt
@@ -1,6 +1,17 @@
-Cleaned 0/431
-Parsed 1 source files
-Compiled 0 modules
+Cleaned 0/432
+Parsed 2 source files
+Compiled 1 modules
+
+  [1;33mWarning number 32[0m
+  [36m/packages/watch-warnings/src/ModuleA.res[0m:[2m1:5-15[0m
+
+  [1;33m1[0m [2m│[0m let [1;33munusedValue[0m = 42
+  2 [2m│[0m 
+  3 [2m│[0m let hello = () => Console.log("hello")
+
+  unused value unusedValue.
+
+
 
 The field 'ignored-dirs' found in the package config of '@testrepo/deprecated-config' is not supported by ReScript 12's new build system.
 
diff --git a/rewatch/tests/snapshots/dev-dependency-used-by-non-dev-source.txt b/rewatch/tests/snapshots/dev-dependency-used-by-non-dev-source.txt
@@ -1,6 +1,17 @@
-Cleaned 0/431
-Parsed 1 source files
-Compiled 1 modules
+Cleaned 0/432
+Parsed 2 source files
+Compiled 2 modules
+
+  [1;33mWarning number 32[0m
+  [36m/packages/watch-warnings/src/ModuleA.res[0m:[2m1:5-15[0m
+
+  [1;33m1[0m [2m│[0m let [1;33munusedValue[0m = 42
+  2 [2m│[0m 
+  3 [2m│[0m let hello = () => Console.log("hello")
+
+  unused value unusedValue.
+
+
 
 The field 'ignored-dirs' found in the package config of '@testrepo/deprecated-config' is not supported by ReScript 12's new build system.
 
diff --git a/rewatch/tests/snapshots/remove-file.txt b/rewatch/tests/snapshots/remove-file.txt
@@ -1,6 +1,17 @@
-Cleaned 1/431
-Parsed 0 source files
-Compiled 1 modules
+Cleaned 1/432
+Parsed 1 source files
+Compiled 2 modules
+
+  [1;33mWarning number 32[0m
+  [36m/packages/watch-warnings/src/ModuleA.res[0m:[2m1:5-15[0m
+
+  [1;33m1[0m [2m│[0m let [1;33munusedValue[0m = 42
+  2 [2m│[0m 
+  3 [2m│[0m let hello = () => Console.log("hello")
+
+  unused value unusedValue.
+
+
 
 The field 'ignored-dirs' found in the package config of '@testrepo/deprecated-config' is not supported by ReScript 12's new build system.
 
diff --git a/rewatch/tests/snapshots/rename-file-internal-dep-namespace.txt b/rewatch/tests/snapshots/rename-file-internal-dep-namespace.txt
@@ -1,6 +1,17 @@
-Cleaned 1/431
-Parsed 1 source files
-Compiled 2 modules
+Cleaned 1/432
+Parsed 2 source files
+Compiled 3 modules
+
+  [1;33mWarning number 32[0m
+  [36m/packages/watch-warnings/src/ModuleA.res[0m:[2m1:5-15[0m
+
+  [1;33m1[0m [2m│[0m let [1;33munusedValue[0m = 42
+  2 [2m│[0m 
+  3 [2m│[0m let hello = () => Console.log("hello")
+
+  unused value unusedValue.
+
+
 
 The field 'ignored-dirs' found in the package config of '@testrepo/deprecated-config' is not supported by ReScript 12's new build system.
 
diff --git a/rewatch/tests/snapshots/rename-file-internal-dep.txt b/rewatch/tests/snapshots/rename-file-internal-dep.txt
@@ -1,6 +1,17 @@
-Cleaned 1/431
-Parsed 1 source files
-Compiled 2 modules
+Cleaned 1/432
+Parsed 2 source files
+Compiled 3 modules
+
+  [1;33mWarning number 32[0m
+  [36m/packages/watch-warnings/src/ModuleA.res[0m:[2m1:5-15[0m
+
+  [1;33m1[0m [2m│[0m let [1;33munusedValue[0m = 42
+  2 [2m│[0m 
+  3 [2m│[0m let hello = () => Console.log("hello")
+
+  unused value unusedValue.
+
+
 
 The field 'ignored-dirs' found in the package config of '@testrepo/deprecated-config' is not supported by ReScript 12's new build system.
 
diff --git a/rewatch/tests/snapshots/rename-file-with-interface.txt b/rewatch/tests/snapshots/rename-file-with-interface.txt
@@ -1,7 +1,18 @@
 [2K No implementation file found for interface file (skipping): src/ModuleWithInterface.resi
-Cleaned 2/431
-Parsed 1 source files
-Compiled 1 modules
+Cleaned 2/432
+Parsed 2 source files
+Compiled 2 modules
+
+  [1;33mWarning number 32[0m
+  [36m/packages/watch-warnings/src/ModuleA.res[0m:[2m1:5-15[0m
+
+  [1;33m1[0m [2m│[0m let [1;33munusedValue[0m = 42
+  2 [2m│[0m 
+  3 [2m│[0m let hello = () => Console.log("hello")
+
+  unused value unusedValue.
+
+
 
 The field 'ignored-dirs' found in the package config of '@testrepo/deprecated-config' is not supported by ReScript 12's new build system.
 
diff --git a/rewatch/tests/snapshots/rename-file.txt b/rewatch/tests/snapshots/rename-file.txt
diff --git a/rewatch/tests/snapshots/rename-interface-file.txt b/rewatch/tests/snapshots/rename-interface-file.txt
diff --git a/rewatch/tests/suffix/01-custom-suffix.sh b/rewatch/tests/suffix/01-custom-suffix.sh
diff --git a/rewatch/tests/suite.sh b/rewatch/tests/suite.sh
diff --git a/rewatch/tests/watch/02-watch-warnings-persist.sh b/rewatch/tests/watch/02-watch-warnings-persist.sh

-Original file line number
+Diff line change
@@ @@ -0,0 +1,4 @@ @@
 +{
 +  "name": "@testrepo/watch-warnings",
 +  "version": "0.0.1"
 +}