allow us to override srcs in config using go tempate with the build rule

config/config.go

@@ -18,6 +18,7 @@ type KindConfig struct {
 	ProvidedDeps      []string `json:"providedDeps"`
 	DefaultVisibility []string `json:"defaultVisibility"`
 	SrcsArg           string   `json:"srcsArg"`
+	SrcsRuleTemplate  string   `json:"srcsRuleTemplate"`
 }
 
 func (kc *KindConfig) srcsArg() string {
@@ -177,24 +178,27 @@ func (c *Config) GetKind(kind string) *kinds.Kind {
 			SrcsAttr:          k.srcsArg(),
 			DefaultVisibility: k.DefaultVisibility,
 			NonGoSources:      k.NonGoSources,
+			SrcsRuleTemplate:  k.SrcsRuleTemplate,
 		}
 	}
 	if k, ok := c.TestKinds[kind]; ok {
 		return &kinds.Kind{
-			Name:         kind,
-			Type:         kinds.Test,
-			ProvidedDeps: k.ProvidedDeps,
-			SrcsAttr:     k.srcsArg(),
-			NonGoSources: k.NonGoSources,
+			Name:             kind,
+			Type:             kinds.Test,
+			ProvidedDeps:     k.ProvidedDeps,
+			SrcsAttr:         k.srcsArg(),
+			NonGoSources:     k.NonGoSources,
+			SrcsRuleTemplate: k.SrcsRuleTemplate,
 		}
 	}
 	if k, ok := c.BinKinds[kind]; ok {
 		return &kinds.Kind{
-			Name:         kind,
-			Type:         kinds.Bin,
-			ProvidedDeps: k.ProvidedDeps,
-			SrcsAttr:     k.srcsArg(),
-			NonGoSources: k.NonGoSources,
+			Name:             kind,
+			Type:             kinds.Bin,
+			ProvidedDeps:     k.ProvidedDeps,
+			SrcsAttr:         k.srcsArg(),
+			NonGoSources:     k.NonGoSources,
+			SrcsRuleTemplate: k.SrcsRuleTemplate,
 		}
 	}
 	if c.base != nil {

eval/eval.go

@@ -31,12 +31,8 @@ func LookLikeBuildLabel(l string) bool {
 	return strings.HasPrefix("//", l)
 }
 
-func (e *Eval) EvalGlobs(dir string, rule *build.Rule, attrName string) ([]string, error) {
-	return e.evalGlobs(dir, rule.Attr(attrName))
-}
-
-func (e *Eval) evalGlobs(dir string, val build.Expr) ([]string, error) {
-	switch expr := val.(type) {
+func (e *Eval) EvalGlobs(dir string, srcs build.Expr) ([]string, error) {
+	switch expr := srcs.(type) {
 	case *build.CallExpr:
 		globArgs := parseGlob(expr)
 		if globArgs == nil {
@@ -47,11 +43,11 @@ func (e *Eval) evalGlobs(dir string, val build.Expr) ([]string, error) {
 		if expr.Op != "+" {
 			return nil, fmt.Errorf("encountered a binary expression with operation %s. Only + is supported", expr.Op)
 		}
-		x, err := e.evalGlobs(dir, expr.X)
+		x, err := e.EvalGlobs(dir, expr.X)
 		if err != nil {
 			return nil, err
 		}
-		y, err := e.evalGlobs(dir, expr.Y)
+		y, err := e.EvalGlobs(dir, expr.Y)
 		if err != nil {
 			return nil, err
 		}
@@ -61,8 +57,8 @@ func (e *Eval) evalGlobs(dir string, val build.Expr) ([]string, error) {
 	}
 }
 
-func (e *Eval) BuildSources(plzPath, dir string, rule *build.Rule, srcsArg string) ([]string, error) {
-	srcs, err := e.EvalGlobs(dir, rule, srcsArg)
+func (e *Eval) BuildSources(plzPath, dir string, srcsExpr build.Expr) ([]string, error) {
+	srcs, err := e.EvalGlobs(dir, srcsExpr)
 	if err != nil {
 		return nil, err
 	}

eval/eval_test.go

@@ -90,7 +90,7 @@ func TestEvalGlob(t *testing.T) {
 			file, err := build.ParseBuild(test.name, []byte(test.code))
 			require.NoError(t, err)
 			require.Len(t, file.Stmt, 1)
-			got, err := e.evalGlobs("test_project", file.Stmt[0])
+			got, err := e.EvalGlobs("test_project", file.Stmt[0])
 			require.NoError(t, err)
 			assert.ElementsMatch(t, test.expected, got)
 		})

generate/generate.go

@@ -251,7 +251,7 @@ func (u *updater) addNewModules(conf *config.Config) error {
 // the source doesn't actually exist. In which case, this should be removed from the rule, as the user likely deleted
 // the file.
 func (u *updater) allSources(conf *config.Config, r *rule, sourceMap map[string]*GoFile) (passedSources []string, goFiles map[string]*GoFile, err error) {
-	srcs, err := u.eval.BuildSources(conf.GetPlzPath(), r.dir, r.Rule, r.SrcsAttr())
+	srcs, err := u.eval.BuildSources(conf.GetPlzPath(), r.dir, r.Srcs())
 	if err != nil {
 		return nil, nil, err
 	}
@@ -492,7 +492,7 @@ func (u *updater) unallocatedSources(srcs map[string]*GoFile, rules []*rule) ([]
 				break
 			}
 
-			ruleSrcs, err := u.eval.EvalGlobs(rule.dir, rule.Rule, rule.SrcsAttr())
+			ruleSrcs, err := u.eval.EvalGlobs(rule.dir, rule.Srcs())
 			if err != nil {
 				return nil, err
 			}

generate/generate_test.go

@@ -299,7 +299,7 @@ func TestUpdateDeps(t *testing.T) {
 func mustGetSources(t *testing.T, u *updater, rule *rule) []string {
 	t.Helper()
 
-	srcs, err := u.eval.EvalGlobs(rule.dir, rule.Rule, rule.SrcsAttr())
+	srcs, err := u.eval.EvalGlobs(rule.dir, rule.Srcs())
 	require.NoError(t, err)
 	return srcs
 }

generate/rule.go

@@ -1,6 +1,9 @@
 package generate
 
 import (
+	"bytes"
+	"text/template"
+
 	"github.com/please-build/buildtools/build"
 
 	"github.com/please-build/puku/edit"
@@ -11,6 +14,7 @@ type rule struct {
 	dir  string
 	kind *kinds.Kind
 	*build.Rule
+	SrcsOveride build.Expr
 }
 
 // setOrDeleteAttr will make sure the attribute with the given name matches the values passed in. It will keep the
@@ -66,12 +70,18 @@ func (rule *rule) SrcsAttr() string {
 }
 
 func (rule *rule) addSrc(src string) {
+	if rule.SrcsOveride != nil {
+		return
+	}
 	srcsAttr := rule.SrcsAttr()
 	srcs := rule.AttrStrings(srcsAttr)
 	rule.setOrDeleteAttr(srcsAttr, append(srcs, src))
 }
 
 func (rule *rule) removeSrc(rem string) {
+	if rule.SrcsOveride != nil {
+		return
+	}
 	srcsAttr := rule.SrcsAttr()
 	srcs := rule.AttrStrings(srcsAttr)
 	set := make([]string, 0, len(srcs))
@@ -115,8 +125,39 @@ func (rule *rule) isExternal() bool {
 
 func newRule(r *build.Rule, kindType *kinds.Kind, pkgDir string) *rule {
 	return &rule{
-		dir:  pkgDir,
-		kind: kindType,
-		Rule: r,
+		dir:         pkgDir,
+		kind:        kindType,
+		Rule:        r,
+		SrcsOveride: templateSrcs(kindType.SrcsRuleTemplate, r),
+	}
+}
+
+func (rule *rule) Srcs() build.Expr {
+	if rule.SrcsOveride != nil {
+		return rule.SrcsOveride
+	}
+	return rule.Attr(rule.SrcsAttr())
+}
+
+func templateSrcs(templStr string, r *build.Rule) build.Expr {
+	if templStr == "" {
+		return nil
+	}
+	tmpl, err := template.New("test").Parse(templStr)
+	if err != nil {
+		return nil
+	}
+	var buf bytes.Buffer
+	err = tmpl.Execute(&buf, r)
+	if err != nil {
+		return nil
+	}
+	file, err := build.ParseBuild("template", buf.Bytes())
+	if err != nil {
+		return nil
+	}
+	if len(file.Stmt) != 1 {
+		return nil
 	}
+	return file.Stmt[0]
 }

kinds/kinds.go

@@ -20,7 +20,8 @@ type Kind struct {
 	SrcsAttr          string
 	// NonGoSources indicates the puku that the sources to this rule are not go so we shouldn't try to parse them to
 	// infer their deps, for example, proto_library.
-	NonGoSources bool
+	NonGoSources     bool
+	SrcsRuleTemplate string
 }
 
 // IsProvided returns whether the dependency is already provided by the kind, and therefore can be omitted from the deps