Fix URL related escaping for oauth2 (#37334)

Follow up #37327. See the comments.

* Root problem: the design of OAuth2 providers is a mess, the display
name is used as provider's name and used in the URL directly
* The regressions:
* When trying to fix https://github.com/go-gitea/gitea/issues/36409 , it
introduced inconsistent URL escaping for the "path" part.
* This fix: always use "path escaping" for the path part, add more tests
to cover all escaping cases.

Now, frontend "pathEscape" and "pathEscapeSegments" generate exactly the
same result as backend.

modules/templates/helper_test.go

@@ -5,6 +5,7 @@ package templates
 
 import (
 	"html/template"
+	"net/url"
 	"strings"
 	"testing"
 
@@ -169,9 +170,21 @@ func TestQueryBuild(t *testing.T) {
 	})
 }
 
+const queryNonASCII = " !\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~" // all non-letter & non-number chars
+
 func TestQueryEscape(t *testing.T) {
 	// this test is a reference for "urlQueryEscape" in JS
-	in := "!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~" // all non-letter & non-number chars
-	expected := "%21%22%23%24%25%26%27%28%29%2A%2B%2C-.%2F%3A%3B%3C%3D%3E%3F%40%5B%5C%5D%5E_%60%7B%7C%7D~"
-	assert.Equal(t, expected, string(queryEscape(in)))
+	// Special case for space encoding:
+	// * RFC 3986: Uniform Resource Identifier (URI): %20
+	// * WHATWG HTML: application/x-www-form-urlencoded: +
+	// * JavaScript: encodeURIComponent() uses "%20". URLSearchParams uses "+"
+	// * Golang: QueryEscape uses "+"
+	expected := "+%21%22%23%24%25%26%27%28%29%2A%2B%2C-.%2F%3A%3B%3C%3D%3E%3F%40%5B%5C%5D%5E_%60%7B%7C%7D~"
+	assert.Equal(t, expected, url.QueryEscape(queryNonASCII))
+}
+
+func TestPathEscape(t *testing.T) {
+	// this test is a reference for "pathEscape" in JS
+	expected := "%20%21%22%23$%25&%27%28%29%2A+%2C-.%2F:%3B%3C=%3E%3F@%5B%5C%5D%5E_%60%7B%7C%7D~"
+	assert.Equal(t, expected, url.PathEscape(queryNonASCII))
 }

modules/util/util_test.go

@@ -184,3 +184,10 @@ func TestOptionalArg(t *testing.T) {
 	assert.Equal(t, 42, bar(nil))
 	assert.Equal(t, 100, bar(nil, 100))
 }
+
+func TestPathEscapeSegments(t *testing.T) {
+	assert.Equal(t, "a", PathEscapeSegments("a"))
+	assert.Equal(t, "a/b", PathEscapeSegments("a/b"))
+	assert.Equal(t, "a/b%20c", PathEscapeSegments("a/b c"))
+	assert.Equal(t, "a/b+c", PathEscapeSegments("a/b+c"))
+}