Add --checkers to control number of checkers per Program

internal/compiler/program.go

@@ -247,7 +247,13 @@ func (p *Program) initCheckerPool() {
 	if p.opts.CreateCheckerPool != nil {
 		p.checkerPool = p.opts.CreateCheckerPool(p)
 	} else {
-		p.checkerPool = newCheckerPool(core.IfElse(p.SingleThreaded(), 1, 4), p)
+		checkers := 4
+		if p.SingleThreaded() {
+			checkers = 1
+		} else if p.Options().Checkers != nil {
+			checkers = min(max(*p.Options().Checkers, 1), 256)
+		}
+		p.checkerPool = newCheckerPool(checkers, p)
 	}
 }
 

internal/core/compileroptions.go

@@ -148,6 +148,7 @@ type CompilerOptions struct {
 	PprofDir       string   `json:"pprofDir,omitzero"`
 	SingleThreaded Tristate `json:"singleThreaded,omitzero"`
 	Quiet          Tristate `json:"quiet,omitzero"`
+	Checkers       *int     `json:"checkers,omitzero"`
 
 	sourceFileAffectingCompilerOptionsOnce sync.Once
 	sourceFileAffectingCompilerOptions     SourceFileAffectingCompilerOptions

internal/diagnostics/extraDiagnosticMessages.json

@@ -11,6 +11,14 @@
         "category": "Message",
         "code": 100002
     },
+    "Set the number of checkers per project.": {
+        "category": "Message",
+        "code": 100003
+    },
+    "4, unless --singleThreaded is passed.": {
+        "category": "Message",
+        "code": 100004
+    },
     "Non-relative paths are not allowed. Did you forget a leading './'?": {
         "category": "Error",
         "code": 5090

internal/tsoptions/declscompiler.go

@@ -233,6 +233,13 @@ var commonOptionsWithBuild = []*CommandLineOption{
 		Category:    diagnostics.Command_line_Options,
 		Description: diagnostics.Generate_pprof_CPU_Slashmemory_profiles_to_the_given_directory,
 	},
+	{
+		Name:                    "checkers",
+		Kind:                    CommandLineOptionTypeNumber,
+		Category:                diagnostics.Command_line_Options,
+		Description:             diagnostics.Set_the_number_of_checkers_per_project,
+		DefaultValueDescription: diagnostics.X_4_unless_singleThreaded_is_passed,
+	},
 }
 
 var optionsForCompiler = []*CommandLineOption{

internal/tsoptions/parsinghelpers.go

@@ -443,6 +443,8 @@ func parseCompilerOptions(key string, value any, allOptions *core.CompilerOption
 		allOptions.SingleThreaded = ParseTristate(value)
 	case "quiet":
 		allOptions.Quiet = ParseTristate(value)
+	case "checkers":
+		allOptions.Checkers = parseNumber(value)
 	default:
 		// different than any key above
 		return false

testdata/baselines/reference/tsbuild/commandLine/help.js

@@ -126,6 +126,9 @@ Run in single threaded mode.
 --pprofDir
 Generate pprof CPU/memory profiles to the given directory.
 
+--checkers
+Set the number of checkers per project.
+
 --verbose, -v
 Enable verbose logging.
 

testdata/baselines/reference/tsc/commandLine/help-all.js

@@ -17,6 +17,9 @@ Show all compiler options.
 --build, -b
 Build one or more projects and their dependencies, if out of date
 
+--checkers
+Set the number of checkers per project.
+
 --help, -h
 Print this message.