feat: support template.Template.Parse function

resolves: #11

internal/source/template.go

@@ -88,6 +88,15 @@ func evaluateTemplateSelector(ts *template.Template, expression ast.Expr, workin
 				return nil, err
 			}
 			return up.Delims(list[0], list[1]), nil
+		case "Parse":
+			if len(call.Args) != 1 {
+				return nil, contextError(workingDirectory, fileSet, call.Lparen, fmt.Errorf("expected exactly one string literal argument"))
+			}
+			sl, err := evaluateStringLiteralExpression(workingDirectory, fileSet, call.Args[0])
+			if err != nil {
+				return nil, err
+			}
+			return up.Parse(sl)
 		case "New":
 			if len(call.Args) != 1 {
 				return nil, contextError(workingDirectory, fileSet, call.Lparen, fmt.Errorf("expected exactly one string literal argument"))

internal/source/template_test.go

@@ -519,6 +519,33 @@ func TestTemplates(t *testing.T) {
 		})
 		require.ErrorContains(t, err, `expected string literal got wrong`)
 	})
+	t.Run("Parse template name from new", func(t *testing.T) {
+		dir := createTestDir(t, filepath.FromSlash("testdata/parse.txtar"))
+		goFiles, fileSet := parseGo(t, dir)
+		ts, err := source.Templates(dir, "templates", fileSet, goFiles, nil)
+		require.NoError(t, err)
+		assert.NotNil(t, ts.Lookup("GET /"))
+	})
+	t.Run("Parse string has multiple routes", func(t *testing.T) {
+		dir := createTestDir(t, filepath.FromSlash("testdata/parse.txtar"))
+		goFiles, fileSet := parseGo(t, dir)
+		ts, err := source.Templates(dir, "multiple", fileSet, goFiles, nil)
+		require.NoError(t, err)
+		assert.NotNil(t, ts.Lookup("GET /"))
+		assert.NotNil(t, ts.Lookup("GET /{name}"))
+	})
+	t.Run("Parse is missing argument", func(t *testing.T) {
+		dir := createTestDir(t, filepath.FromSlash("testdata/parse.txtar"))
+		goFiles, fileSet := parseGo(t, dir)
+		_, err := source.Templates(dir, "noArg", fileSet, goFiles, nil)
+		require.ErrorContains(t, err, "run template noArg failed at parse.go:12:35: expected exactly one string literal argument")
+	})
+	t.Run("Parse gets wrong argument type", func(t *testing.T) {
+		dir := createTestDir(t, filepath.FromSlash("testdata/parse.txtar"))
+		goFiles, fileSet := parseGo(t, dir)
+		_, err := source.Templates(dir, "wrongArg", fileSet, goFiles, nil)
+		require.ErrorContains(t, err, "run template wrongArg failed at parse.go:14:40: expected string literal got 500")
+	})
 }
 
 func createTestDir(t *testing.T, filename string) string {

internal/source/testdata/parse.txtar

@@ -0,0 +1,15 @@
+-- parse.go --
+package main
+
+import "html/template"
+
+var templates = template.New("GET /").Parse(`<h1>Hello, world!</h1>`)
+
+var multiple = template.New("").Parse(`
+{{define "GET /"}}<h1>Hello, world!</h1>{{end}}
+{{define "GET /{name}"}}<h1>Hello, {{.PathValue "name"}}!</h1>{{end}}
+`)
+
+var noArg = template.New("").Parse()
+
+var wrongArg =  template.New("").Parse(500)