html/template, text/template: add ParseFS

Now templates can be parsed not just from operating system files
but from arbitrary file systems, including zip files.

For #41190.

Change-Id: I2172001388ddb1f13defa6c5e644e8ec8703ee80
Reviewed-on: https://go-review.googlesource.com/c/go/+/243938
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

1 files changed, 43 insertions, 0 deletions

diff --git a/src/html/template/multi_test.go b/src/html/template/multi_test.go
index 50526c5b65..6535ab6c04 100644
--- a/src/html/template/multi_test.go
+++ b/src/html/template/multi_test.go
@@ -7,7 +7,9 @@
 package template
 
 import (
+	"archive/zip"
 	"bytes"
+	"os"
 	"testing"
 	"text/template/parse"
 )
@@ -82,6 +84,35 @@ func TestParseGlob(t *testing.T) {
 	testExecute(multiExecTests, template, t)
 }
 
+func TestParseFS(t *testing.T) {
+	fs := os.DirFS("testdata")
+
+	{
+		_, err := ParseFS(fs, "DOES NOT EXIST")
+		if err == nil {
+			t.Error("expected error for non-existent file; got none")
+		}
+	}
+
+	{
+		template := New("root")
+		_, err := template.ParseFS(fs, "file1.tmpl", "file2.tmpl")
+		if err != nil {
+			t.Fatalf("error parsing files: %v", err)
+		}
+		testExecute(multiExecTests, template, t)
+	}
+
+	{
+		template := New("root")
+		_, err := template.ParseFS(fs, "file*.tmpl")
+		if err != nil {
+			t.Fatalf("error parsing files: %v", err)
+		}
+		testExecute(multiExecTests, template, t)
+	}
+}
+
 // In these tests, actual content (not just template definitions) comes from the parsed files.
 
 var templateFileExecTests = []execTest{
@@ -104,6 +135,18 @@ func TestParseGlobWithData(t *testing.T) {
 	testExecute(templateFileExecTests, template, t)
 }
 
+func TestParseZipFS(t *testing.T) {
+	z, err := zip.OpenReader("testdata/fs.zip")
+	if err != nil {
+		t.Fatalf("error parsing zip: %v", err)
+	}
+	template, err := New("root").ParseFS(z, "tmpl*.tmpl")
+	if err != nil {
+		t.Fatalf("error parsing files: %v", err)
+	}
+	testExecute(templateFileExecTests, template, t)
+}
+
 const (
 	cloneText1 = `{{define "a"}}{{template "b"}}{{template "c"}}{{end}}`
 	cloneText2 = `{{define "b"}}b{{end}}`