Go: Initialise go.mod for stray source files

Author: mbg

go/extractor/project/project.go

@@ -301,6 +301,7 @@ func getBuildRoots(emitDiagnostics bool) (goWorkspaces []GoWorkspace, totalModul
 		goWorkspaces = []GoWorkspace{{
 			BaseDir: ".",
 			DepMode: GoGetWithModules,
+			Modules: loadGoModules([]string{"go.mod"}),
 			ModMode: getModMode(GoGetWithModules, "."),
 		}}
 		totalModuleFiles = 1
@@ -324,12 +325,16 @@ func getBuildRoots(emitDiagnostics bool) (goWorkspaces []GoWorkspace, totalModul
 			diagnostics.EmitGoFilesOutsideGoModules(goModPaths)
 		}
 
-		goWorkspaces = []GoWorkspace{{
+		// Try to initialize a `go.mod` file automatically for the stray source files.
+		initGoModForLegacyProject(".")
+
+		goWorkspaces = append(goWorkspaces, GoWorkspace{
 			BaseDir: ".",
-			DepMode: GoGetNoModules,
+			Modules: loadGoModules([]string{"go.mod"}),
+			DepMode: GoGetWithModules,
 			ModMode: ModUnset,
-		}}
-		totalModuleFiles = 0
+		})
+		totalModuleFiles += 1
 		return
 	}
 

go/ql/integration-tests/all-platforms/go/single-go-mod-and-go-files-not-under-it/test.expected

@@ -1,7 +1,7 @@
 extractedFiles
+| src/go.mod:0:0:0:0 | src/go.mod |
 | src/main.go:0:0:0:0 | src/main.go |
+| src/subdir/go.mod:0:0:0:0 | src/subdir/go.mod |
 | src/subdir/subsubdir/add.go:0:0:0:0 | src/subdir/subsubdir/add.go |
 | src/subdir/test.go:0:0:0:0 | src/subdir/test.go |
 #select
-| Extraction failed in subdir/test.go with error cannot find package "subdir/subsubdir" in any of:\n\t(absolute path) (from $GOROOT)\n\t(absolute path) (from $GOPATH) | 2 |
-| Extraction failed in subdir/test.go with error could not import subdir/subsubdir (invalid package name: "") | 2 |