Passing --force option to build, builds project from start

src/compiler/tsbuild.ts

@@ -1178,6 +1178,7 @@ namespace ts {
         }
 
         function getOldProgram(proj: ResolvedConfigFileName, parsed: ParsedCommandLine) {
+            if (options.force) return undefined;
             const value = builderPrograms.getValue(proj);
             if (value) return value;
             return readBuilderProgram(parsed.options, readFileWithCache) as any as T;

src/testRunner/unittests/tsbuild/sample.ts

@@ -168,14 +168,14 @@ namespace ts {
         });
 
         describe("can detect when and what to rebuild", () => {
-            function initializeWithBuild() {
+            function initializeWithBuild(opts?: BuildOptions) {
                 const fs = projFs.shadow();
                 const host = new fakes.SolutionBuilderHost(fs);
                 const builder = createSolutionBuilder(host, ["/src/tests"], { verbose: true });
                 builder.buildAllProjects();
                 host.clearDiagnostics();
                 tick();
-                builder.resetBuildContext();
+                builder.resetBuildContext(opts ? { ...opts, verbose: true } : undefined);
                 return { fs, host, builder };
             }
 
@@ -254,6 +254,20 @@ namespace ts {
                     [Diagnostics.Building_project_0, "/src/tests/tsconfig.json"],
                 );
             });
+
+            it("rebuilds from start if --f is passed", () => {
+                const { host, builder } = initializeWithBuild({ force: true });
+                builder.buildAllProjects();
+                host.assertDiagnosticMessages(
+                    getExpectedDiagnosticForProjectsInBuild("src/core/tsconfig.json", "src/logic/tsconfig.json", "src/tests/tsconfig.json"),
+                    [Diagnostics.Project_0_is_up_to_date_because_newest_input_1_is_older_than_oldest_output_2, "src/core/tsconfig.json", "src/core/anotherModule.ts", "src/core/anotherModule.js"],
+                    [Diagnostics.Building_project_0, "/src/core/tsconfig.json"],
+                    [Diagnostics.Project_0_is_up_to_date_with_d_ts_files_from_its_dependencies, "src/logic/tsconfig.json"],
+                    [Diagnostics.Building_project_0, "/src/logic/tsconfig.json"],
+                    [Diagnostics.Project_0_is_up_to_date_with_d_ts_files_from_its_dependencies, "src/tests/tsconfig.json"],
+                    [Diagnostics.Building_project_0, "/src/tests/tsconfig.json"]
+                );
+            });
         });
 
         describe("downstream-blocked compilations", () => {