Relative multi-line HTML elements

Reintroduces "relative multi-line" indentation to DjHTML:

    <long-html-tag
        attribute1="value"
        attribute2="value"
        attribute3="value"/>

However, this only happens when the tag name is followed by a newline.
Otherwise, "absolute multi-line" indentation will be used:

    <long-html-tag attribute1="value"
                   attribute2="value"
                   attribute3="value"/>

This is a good rule, but also the last rule I'm willing to add regarding
multi-line indentation. Our users deserve a stable set of indentation
principles, and this is it. No more bikeshedding.

djhtml/modes.py

@@ -287,9 +287,19 @@ def create_token(self, raw_token, src, line):
 
         if raw_token == "<":
             if tag := re.match(r"([\w\-\.:]+)", src):
-                token, mode = Token.Text(raw_token, mode=DjHTML), InsideHTMLTag(
-                    tag[1], line, self
+                tagname = tag[1]
+                absolute = True
+                token = Token.Text(raw_token, mode=DjHTML)
+                offsets = dict(
+                    relative=-1 if line.indents else 0,
+                    absolute=len(line) + len(tagname) + 2,
                 )
+                if tag := re.match(tagname + r"*\n", src):
+                    # Use "relative" multi-line indendation instead
+                    absolute = False
+                    token.indents = True
+                    offsets = dict(relative=0, absolute=0)
+                mode = InsideHTMLTag(tagname, line, self, absolute, offsets)
             else:
                 token = Token.Text(raw_token, mode=DjHTML)
         elif raw_token == "<!--":
@@ -513,17 +523,14 @@ class InsideHTMLTag(DjTXT):
 
     RAW_TOKENS = DjTXT.RAW_TOKENS + [r"/?>", r"[^ ='\">/\n]+=", r'"', r"'"]
 
-    def __init__(self, tagname, line, return_mode):
+    def __init__(self, tagname, line, return_mode, absolute, offsets):
         self.tagname = tagname
         self.return_mode = return_mode
+        self.absolute = absolute
+        self.offsets = offsets
         self.token_re = compile_re(self.RAW_TOKENS)
         self.inside_attr = False
-        self.offsets = dict(
-            relative=-1 if line.indents else 0, absolute=len(line) + len(tagname) + 2
-        )
-
-        # Pff...
-        self.additional_offset = -len(tagname) - 1
+        self.additional_offset = -len(tagname) - 1 if absolute else 0
 
     def create_token(self, raw_token, src, line):
         mode = self
@@ -549,6 +556,8 @@ def create_token(self, raw_token, src, line):
                 token = Token.Text(raw_token, mode=InsideHTMLTag, **self.offsets)
         elif not self.inside_attr and raw_token == "/>":
             token, mode = Token.Text(raw_token, mode=DjHTML), self.return_mode
+            if not self.absolute:
+                token.dedents = True
         elif not self.inside_attr and raw_token == ">":
             if self.tagname.lower() in DjHTML.IGNORE_TAGS:
                 token, mode = Token.Text(raw_token, mode=DjHTML), self.return_mode
@@ -565,6 +574,8 @@ def create_token(self, raw_token, src, line):
                     Token.Open(raw_token, mode=DjHTML),
                     self.return_mode,
                 )
+            if not self.absolute:
+                token.dedents = True
         else:
             token, mode = super().create_token(raw_token, src, line)
 

tests/suite/html.html

@@ -132,18 +132,18 @@ <h1>Title</h1>
 <!-- SVG with multi-line attribute values -->
 <svg width="325" height="325" xmlns="http://www.w3.org/2000/svg">
     <path
-          d="M 80 80
-             A 45 45, 0, 0, 0, 125 125
-             L 125 80 Z"
-          fill="green"
+        d="M 80 80
+           A 45 45, 0, 0, 0, 125 125
+           L 125 80 Z"
+        fill="green"
     />
     <path
-          d="
-             M 80 80
-             A 45 45, 0, 0, 0, 125 125
-             L 125 80 Z
-            "
-          fill="green"
+        d="
+           M 80 80
+           A 45 45, 0, 0, 0, 125 125
+           L 125 80 Z
+          "
+        fill="green"
     />
     <path d="M 80 80
              A 45 45, 0, 0, 0, 125 125
@@ -161,20 +161,20 @@ <h1>Title</h1>
 
 <!-- Block tags inside HTML elements -->
 <div
-     {% block class %}
-         class="foo"
-     {% endblock %}
+    {% block class %}
+        class="foo"
+    {% endblock %}
 >
     text
 </div>
 
 <div
-     {% block classes %}
-         class="
-                foo
-                bar
-               "
-     {% endblock %}
+    {% block classes %}
+        class="
+               foo
+               bar
+              "
+    {% endblock %}
 >
     text
 </div>
@@ -227,8 +227,8 @@ <h1>Title</h1>
     text
 </a>
 <a
-   id="2" href=""
-   class="button">
+    id="2" href=""
+    class="button">
     text
 </a>
 <a id="3" href=""
@@ -237,8 +237,8 @@ <h1>Title</h1>
     text
 </a>
 <a
-   id="4" href=""
-   class="button"
+    id="4" href=""
+    class="button"
 >
     text
 </a>
@@ -306,11 +306,11 @@ <h1>Title</h1>
 
 <!-- Weird but legal element names -->
 <my-component
-              hidden/>
+    hidden/>
 <my.component
-              hidden/>
+    hidden/>
 <my:component
-              hidden/>
+    hidden/>
 
 
 <!-- Multi-line attribute value with additional elements/attributes -->
@@ -352,3 +352,14 @@ <h1>Title</h1>
             class="baz'
                   "
 />
+
+
+<!-- Absolute vs. relative mult-line elements -->
+<long-html-tag attribute1="value"
+               attribute2="value"
+               attribute3="value"/>
+
+<long-html-tag-followed-by-newline
+    attribute1="value"
+    attribute2="value"
+    attribute3="value"/>