Fix #16708 / Some errors are not reported if any of previous files contain errors (#16719)

* test

* See what happens...

* potential fix

* revert

* what about this

* f

* Release note

* revert

---------

Co-authored-by: Vlad Zarytovskii <[email protected]>

Author: 0101

docs/release-notes/.FSharp.Compiler.Service/8.0.300.md

@@ -13,6 +13,7 @@
 * `[<CliEvent>]` member should not produce property symbol. ([Issue #16640](https://github.com/dotnet/fsharp/issues/16640), [PR #16658](https://github.com/dotnet/fsharp/pull/16658))
 * Fix discriminated union initialization. ([#PR 16661](https://github.com/dotnet/fsharp/pull/16661))
 * Allow calling method with both Optional and ParamArray. ([#PR 16688](https://github.com/dotnet/fsharp/pull/16688), [suggestions #1120](https://github.com/fsharp/fslang-suggestions/issues/1120))
+* Return diagnostics that got suppressed by errors in previous files. ([PR #16719](https://github.com/dotnet/fsharp/pull/16719))
 * Fix release inline optimization, which leads to MethodAccessException if used with `assembly:InternalsVisibleTo`` attribute. ([Issue #16105](https://github.com/dotnet/fsharp/issues/16105), ([PR #16737](https://github.com/dotnet/fsharp/pull/16737))
 * Enforce AttributeTargets on let values and functions. ([PR #16692](https://github.com/dotnet/fsharp/pull/16692))
 * Enforce AttributeTargets on union case declarations. ([PR #16764](https://github.com/dotnet/fsharp/pull/16764))

src/Compiler/Service/FSharpCheckerResults.fs

@@ -2909,11 +2909,6 @@ module internal ParseAndCheckFile =
             // update the error handler with the modified tcConfig
             errHandler.DiagnosticOptions <- tcConfig.diagnosticsOptions
 
-            // Play background errors and warnings for this file.
-            do
-                for err, severity in backgroundDiagnostics do
-                    diagnosticSink (err, severity)
-
             // If additional references were brought in by the preprocessor then we need to process them
             ApplyLoadClosure(tcConfig, parsedMainInput, mainInputFileName, loadClosure, tcImports, backgroundDiagnostics)
 
@@ -2957,6 +2952,11 @@ module internal ParseAndCheckFile =
                         return ((tcState.TcEnvFromSignatures, EmptyTopAttrs, [], [ mty ]), tcState)
                 }
 
+            // Play background errors and warnings for this file.
+            do
+                for err, severity in backgroundDiagnostics do
+                    diagnosticSink (err, severity)
+
             let (tcEnvAtEnd, _, implFiles, ccuSigsForFiles), tcState = resOpt
 
             let symbolEnv = SymbolEnv(tcGlobals, tcState.Ccu, Some tcState.CcuSig, tcImports)

tests/FSharp.Compiler.ComponentTests/FSharpChecker/CommonWorkflows.fs

@@ -166,3 +166,31 @@ let GetAllUsesOfAllSymbols() =
     traceProvider.Dispose()
 
     if result.Length <> 79 then failwith $"Expected 79 symbolUses, got {result.Length}:\n%A{result}"
+
+[<Fact>]
+let ``We don't lose subsequent diagnostics when there's error in one file`` () =
+    let project =
+        { SyntheticProject.Create(
+            { sourceFile "First" [] with
+                Source = """module AbstractBaseClass.File1 
+                
+                let foo x = ()
+                
+                a""" },
+            { sourceFile "Second" [] with
+                Source = """module AbstractBaseClass.File2
+
+                open AbstractBaseClass.File1
+
+                let goo = foo 1
+
+                type AbstractBaseClass() =
+
+                    abstract P: int""" }) with
+            AutoAddModules = false
+            SkipInitialCheck = true }
+                
+    project.Workflow {
+        checkFile "First" (expectErrorCodes ["FS0039"])
+        checkFile "Second" (expectErrorCodes ["FS0054"; "FS0365"])
+    }

tests/FSharp.Test.Utilities/ProjectGeneration.fs

@@ -725,6 +725,19 @@ module ProjectOperations =
             then
                 failwith "Expected errors, but there were none"
 
+    let expectErrorCodes codes parseAndCheckResults _ =
+        let (parseResult: FSharpParseFileResults), _checkResult = parseAndCheckResults
+
+        if not parseResult.ParseHadErrors then
+            let checkResult = getTypeCheckResult parseAndCheckResults
+            let actualCodes = checkResult.Diagnostics |> Seq.map (fun d -> d.ErrorNumberText) |> Set
+            let codes = Set.ofSeq codes
+            if actualCodes <> codes then
+                failwith $"Expected error codes {codes} but got {actualCodes}. \n%A{checkResult.Diagnostics}"
+
+        else
+            failwith $"There were parse errors: %A{parseResult.Diagnostics}"
+
     let expectSignatureChanged result (oldSignature: string, newSignature: string) =
         expectOk result ()
         Assert.NotEqual<string>(oldSignature, newSignature)