C#: Add compilation errors to the debug log in BMN.

csharp/extractor/Semmle.Extraction.CSharp/Extractor/Analyser.cs

@@ -360,5 +360,22 @@ private static string Version
                 return versionString.InformationalVersion;
             }
         }
+
+        private static readonly HashSet<string> errorsToIgnore = new HashSet<string>
+        {
+            "CS7027",   // Code signing failure
+            "CS1589",   // XML referencing not supported
+            "CS1569"    // Error writing XML documentation
+        };
+
+        /// <summary>
+        /// Retrieves the diagnostics from the compilation, filtering out those that should be ignored.
+        /// </summary>
+        protected List<Diagnostic> GetFilteredDiagnostics() =>
+            compilation is not null
+                ? compilation.GetDiagnostics()
+                    .Where(e => e.Severity >= DiagnosticSeverity.Error && !errorsToIgnore.Contains(e.Id))
+                    .ToList()
+                : [];
     }
 }

csharp/extractor/Semmle.Extraction.CSharp/Extractor/StandaloneAnalyser.cs

@@ -13,13 +13,22 @@ public StandaloneAnalyser(IProgressMonitor pm, ILogger logger, PathTransformer p
         {
         }
 
+        private void LogDiagnostics()
+        {
+            foreach (var error in GetFilteredDiagnostics())
+            {
+                Logger.LogDebug($"  Compilation error: {error}");
+            }
+        }
+
         public void Initialize(string outputPath, IEnumerable<(string, string)> compilationInfos, CSharpCompilation compilationIn, CommonOptions options)
         {
             compilation = compilationIn;
             ExtractionContext = new ExtractionContext(Directory.GetCurrentDirectory(), [], outputPath, compilationInfos, Logger, PathTransformer, ExtractorMode.Standalone, options.QlTest);
             this.options = options;
             LogExtractorInfo();
             SetReferencePaths();
+            LogDiagnostics();
         }
     }
 }

csharp/extractor/Semmle.Extraction.CSharp/Extractor/TracingAnalyser.cs

@@ -136,32 +136,21 @@ internal static string GetOutputName(CSharpCompilation compilation,
 
         private int LogDiagnostics()
         {
-            var filteredDiagnostics = compilation!
-                .GetDiagnostics()
-                .Where(e => e.Severity >= DiagnosticSeverity.Error && !errorsToIgnore.Contains(e.Id))
-                .ToList();
-
+            var filteredDiagnostics = GetFilteredDiagnostics();
             foreach (var error in filteredDiagnostics)
             {
                 Logger.LogError($"  Compilation error: {error}");
             }
 
             if (filteredDiagnostics.Count != 0)
             {
-                foreach (var reference in compilation.References)
+                foreach (var reference in compilation!.References)
                 {
                     Logger.LogInfo($"  Resolved reference {reference.Display}");
                 }
             }
 
             return filteredDiagnostics.Count;
         }
-
-        private static readonly HashSet<string> errorsToIgnore = new HashSet<string>
-        {
-            "CS7027",   // Code signing failure
-            "CS1589",   // XML referencing not supported
-            "CS1569"    // Error writing XML documentation
-        };
     }
 }

csharp/ql/lib/change-notes/2025-11-17-compiler-error-debug.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Compilation errors are now included in the debug log when using build-mode none.