Add diagnostic for missing project files

csharp/autobuilder/Semmle.Autobuild.CSharp/CSharpDiagnosticClassifier.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using System.Text.RegularExpressions;
 using Semmle.Autobuild.Shared;
@@ -56,6 +57,70 @@ namespace Semmle.Autobuild.CSharp
         }
     }
 
+    public class MissingProjectFileRule : DiagnosticRule
+    {
+        private const string runsOnDocsUrl = "https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idruns-on";
+        private const string checkoutDocsUrl = "https://github.com/actions/checkout#usage";
+
+        public class Result : IDiagnosticsResult
+        {
+            /// <summary>
+            /// A set of missing project files.
+            /// </summary>
+            public HashSet<string> MissingProjectFiles { get; }
+
+            public Result()
+            {
+                this.MissingProjectFiles = new HashSet<string>();
+            }
+
+            public DiagnosticMessage ToDiagnosticMessage<T>(Autobuilder<T> builder) where T : AutobuildOptionsShared
+            {
+                var diag = builder.MakeDiagnostic(
+                    $"missing-project-files",
+                    $"Missing project files"
+                );
+                diag.MarkdownMessage =
+                    "Some project files were not found when CodeQL built your project:\n\n" +
+                    this.MissingProjectFiles.AsEnumerable().ToMarkdownList(MarkdownUtil.CodeFormatter, 5) +
+                    "\n\nThis may lead to subsequent failures. " +
+                    "You can check for common causes for missing project files:\n\n" +
+                    $"- Ensure that the project is built using the {runsOnDocsUrl.ToMarkdownLink("intended operating system")} and that filenames on case-sensitive platforms are correctly specified.\n" +
+                    $"- If your repository uses Git submodules, ensure that those are {checkoutDocsUrl.ToMarkdownLink("checked out")} before the CodeQL action is run.\n" +
+                    "- If you auto-generate some project files as part of your build process, ensure that these are generated before the CodeQL action is run.";
+                diag.Severity = DiagnosticMessage.TspSeverity.Warning;
+
+                return diag;
+            }
+        }
+
+        public MissingProjectFileRule() :
+            base("MSB3202: The project file \"(?<projectFile>[^\"]+)\" was not found. \\[(?<location>[^\\]]+)\\]")
+        {
+        }
+
+        public override void Fire(DiagnosticClassifier classifier, Match match)
+        {
+            if (!match.Groups.TryGetValue("projectFile", out var projectFile))
+                throw new ArgumentException("Expected regular expression match to contain projectFile");
+            if (!match.Groups.TryGetValue("location", out var location))
+                throw new ArgumentException("Expected regular expression match to contain location");
+
+            var result = classifier.Results.OfType<Result>().FirstOrDefault();
+
+            // if we do not yet have a result for this rule, create one and add it to the list
+            // of results the classifier knows about
+            if (result is null)
+            {
+                result = new Result();
+                classifier.Results.Add(result);
+            }
+
+            // then add the missing project file
+            result.MissingProjectFiles.Add(projectFile.Value);
+        }
+    }
+
     /// <summary>
     /// Implements a <see cref="DiagnosticClassifier" /> which applies C#-specific rules to
     /// the build output.
@@ -66,6 +131,7 @@ namespace Semmle.Autobuild.CSharp
         {
             // add C#-specific rules to this classifier
             this.AddRule(new MissingXamarinSdkRule());
+            this.AddRule(new MissingProjectFileRule());
         }
     }
 }

csharp/autobuilder/Semmle.Autobuild.Shared/MarkdownUtil.cs

@@ -13,6 +13,14 @@ namespace Semmle.Autobuild.Shared
         /// <returns>A function which formats items as markdown inline code.</returns>
         public static readonly Func<string, string> CodeFormatter = item => $"`{item}`";
 
+        /// <summary>
+        /// Formats the string as a markdown link.
+        /// </summary>
+        /// <param name="link">The URL for the link.</param>
+        /// <param name="title">The text that is displayed.</param>
+        /// <returns>A string containing a markdown-formatted link.</returns>
+        public static string ToMarkdownLink(this string link, string title) => $"[{title}]({link})";
+
         /// <summary>
         /// Renders <see cref="projects" /> as a markdown list of the project paths.
         /// </summary>