lang: Plumb data and unification strategy through the lang struct

This adds some plumbing to pass values into the lang struct.

lang/gapi/gapi.go

@@ -70,6 +70,9 @@ func init() {
 type GAPI struct {
 	InputURI string // input URI of code file system to run
 
+	// Data is some additional data for the lang struct.
+	Data *lang.Data
+
 	lang   *lang.Lang // lang struct
 	wgRun  *sync.WaitGroup
 	ctx    context.Context
@@ -261,6 +264,11 @@ func (obj *GAPI) Cli(info *gapi.Info) (*gapi.Deploy, error) {
 		return nil, nil // success!
 	}
 
+	unificationStrategy := make(map[string]string)
+	if name := args.UnifySolver; name != nil && *name != "" {
+		unificationStrategy[unification.StrategyNameKey] = *name
+	}
+
 	if !args.SkipUnify {
 		// apply type unification
 		unificationLogf := func(format string, v ...interface{}) {
@@ -275,10 +283,11 @@ func (obj *GAPI) Cli(info *gapi.Info) (*gapi.Deploy, error) {
 			return nil, errwrap.Wrapf(err, "could not get default solver")
 		}
 		unifier := &unification.Unifier{
-			AST:    iast,
-			Solver: solver,
-			Debug:  debug,
-			Logf:   unificationLogf,
+			AST:      iast,
+			Solver:   solver,
+			Strategy: unificationStrategy,
+			Debug:    debug,
+			Logf:     unificationLogf,
 		}
 		startTime := time.Now()
 		unifyErr := unifier.Unify(context.TODO())
@@ -411,7 +420,10 @@ func (obj *GAPI) Cli(info *gapi.Info) (*gapi.Deploy, error) {
 		Sema: info.Flags.Sema,
 		GAPI: &GAPI{
 			InputURI: fs.URI(),
-			// TODO: add properties here...
+			Data: &lang.Data{
+				UnificationStrategy: unificationStrategy,
+				// TODO: add properties here...
+			},
 		},
 	}, nil
 }
@@ -451,6 +463,7 @@ func (obj *GAPI) LangInit(ctx context.Context) error {
 		Fs:    fs,
 		FsURI: obj.InputURI,
 		Input: input,
+		Data:  obj.Data,
 
 		Hostname: obj.data.Hostname,
 		Local:    obj.data.Local,

lang/lang.go

@@ -64,6 +64,18 @@ const (
 	EngineStartupStatsTimeout = 10
 )
 
+// Data is some data that is passed into the Lang struct. It is presented here
+// as a single struct with room for multiple fields so that it can be changed or
+// extended in the future without having to re-plumb through all the fields it
+// contains
+type Data struct {
+	// UnificationStrategy is a hack to tune unification performance until
+	// we have an overall cleaner unification algorithm in place.
+	UnificationStrategy map[string]string
+
+	// TODO: Add other fields here if necessary.
+}
+
 // Lang is the main language lexer/parser object.
 type Lang struct {
 	Fs    engine.Fs // connected fs where input dir or metadata exists
@@ -79,6 +91,9 @@ type Lang struct {
 	// run the raw string as mcl code.
 	Input string
 
+	// Data is some additional data for the lang struct.
+	Data *Data
+
 	Hostname string
 	Local    *local.API
 	World    engine.World
@@ -101,6 +116,12 @@ type Lang struct {
 // watching them, *before* we pull their values, that way we'll know if they
 // changed from the values we wanted.
 func (obj *Lang) Init(ctx context.Context) error {
+	if obj.Data == nil {
+		return fmt.Errorf("lang struct was not built properly")
+	}
+	if obj.Data.UnificationStrategy == nil {
+		return fmt.Errorf("lang struct was not built properly")
+	}
 	if obj.Debug {
 		obj.Logf("input: %s", obj.Input)
 		tree, err := util.FsTree(obj.Fs, "/") // should look like gapi
@@ -227,15 +248,20 @@ func (obj *Lang) Init(ctx context.Context) error {
 	}
 	obj.Logf("running type unification...")
 
-	solver, err := unification.LookupDefault()
-	if err != nil {
+	var solver unification.Solver
+	if name, exists := obj.Data.UnificationStrategy["solver"]; exists && name != "" {
+		if solver, err = unification.Lookup(name); err != nil {
+			return errwrap.Wrapf(err, "could not get solver: %s", name)
+		}
+	} else if solver, err = unification.LookupDefault(); err != nil {
 		return errwrap.Wrapf(err, "could not get default solver")
 	}
 	unifier := &unification.Unifier{
-		AST:    obj.ast,
-		Solver: solver,
-		Debug:  obj.Debug,
-		Logf:   logf,
+		AST:      obj.ast,
+		Solver:   solver,
+		Strategy: obj.Data.UnificationStrategy,
+		Debug:    obj.Debug,
+		Logf:     logf,
 	}
 	timing = time.Now()
 	// NOTE: This is the "real" Unify that runs. (This is not for deploy.)

lang/lang_test.go

@@ -137,7 +137,10 @@ func runInterpret(t *testing.T, code string) (_ *pgraph.Graph, reterr error) {
 	lang := &Lang{
 		Fs:    fs,
 		Input: "/" + interfaces.MetadataFilename, // start path in fs
-		Debug: testing.Verbose(),                 // set via the -test.v flag to `go test`
+		Data: &Data{
+			UnificationStrategy: make(map[string]string), // empty
+		},
+		Debug: testing.Verbose(), // set via the -test.v flag to `go test`
 		Logf:  logf,
 	}
 	if err := lang.Init(ctx); err != nil {

lang/unification/interfaces.go

@@ -42,11 +42,18 @@ const (
 	// ErrAmbiguous means we couldn't find a solution, but we weren't
 	// inconsistent.
 	ErrAmbiguous = interfaces.Error("can't unify, no equalities were consumed, we're ambiguous")
+
+	// StrategyNameKey is the string key used when choosing a solver name.
+	StrategyNameKey = "name"
 )
 
 // Init contains some handles that are used to initialize every solver. Each
 // individual solver can choose to omit using some of the fields.
 type Init struct {
+	// Strategy is a hack to tune unification performance until we have an
+	// overall cleaner unification algorithm in place.
+	Strategy map[string]string
+
 	Debug bool
 	Logf  func(format string, v ...interface{})
 }

lang/unification/simplesolver/simplesolver.go

@@ -75,6 +75,8 @@ type SimpleInvariantSolver struct {
 
 // Init contains some handles that are used to initialize the solver.
 func (obj *SimpleInvariantSolver) Init(init *unification.Init) error {
+	obj.Strategy = init.Strategy
+
 	obj.Debug = init.Debug
 	obj.Logf = init.Logf
 

lang/unification/unification.go

@@ -48,6 +48,10 @@ type Unifier struct {
 	// Solver is the solver algorithm implementation to use.
 	Solver Solver
 
+	// Strategy is a hack to tune unification performance until we have an
+	// overall cleaner unification algorithm in place.
+	Strategy map[string]string
+
 	Debug bool
 	Logf  func(format string, v ...interface{})
 }
@@ -76,8 +80,9 @@ func (obj *Unifier) Unify(ctx context.Context) error {
 	}
 
 	init := &Init{
-		Logf:  obj.Logf,
-		Debug: obj.Debug,
+		Strategy: obj.Strategy,
+		Logf:     obj.Logf,
+		Debug:    obj.Debug,
 	}
 	if err := obj.Solver.Init(init); err != nil {
 		return err