From 23981f82cea41ceb3fffbd40449b15697a945e33 Mon Sep 17 00:00:00 2001
From: John Doty <john@d0ty.me>
Date: Fri, 6 Sep 2024 10:20:34 -0700
Subject: [PATCH] Start working on emacs mode generation

---
 parser/emacs.py | 120 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 120 insertions(+)
 create mode 100644 parser/emacs.py

diff --git a/parser/emacs.py b/parser/emacs.py
new file mode 100644
index 0000000..2f51c0b
--- /dev/null
+++ b/parser/emacs.py
@@ -0,0 +1,120 @@
+# https://www.masteringemacs.org/article/lets-write-a-treesitter-major-mode
+import dataclasses
+import itertools
+import pathlib
+import textwrap
+
+from parser.tree_sitter import terminal_name
+
+from . import parser
+
+
+@dataclasses.dataclass(frozen=True, order=True)
+class FaceQuery:
+    feature: str  # Important to be first!
+    face: str
+    node: str
+    field: str | None
+
+
+def gather_faces(grammar: parser.Grammar):
+    nts = {nt.name: nt for nt in grammar.non_terminals()}
+
+    def scoop(node: str, input: parser.FlattenedWithMetadata, visited: set[str]) -> list[FaceQuery]:
+        parts = []
+        for item in input:
+            if isinstance(item, tuple):
+                meta, sub = item
+                parts.extend(scoop(node, sub, visited))
+
+                highlight = meta.get("highlight")
+                if isinstance(highlight, parser.HighlightMeta):
+                    field_name = meta.get("field")
+                    if not isinstance(field_name, str):
+                        raise Exception("Highlight must come with a field name")  # TODO
+
+                    feature = highlight.font_lock_feature
+                    face = highlight.font_lock_face
+                    if feature and face:
+                        parts.append(
+                            FaceQuery(
+                                node=node,
+                                field=field_name,
+                                feature=feature,
+                                face=face,
+                            )
+                        )
+
+            elif isinstance(item, str):
+                nt = nts[item]
+                if nt.transparent:
+                    if nt.name in visited:
+                        continue
+                    visited.add(nt.name)
+                    body = nt.fn(grammar)
+                    for production in body.flatten(with_metadata=True):
+                        parts.extend(scoop(node, production, visited))
+
+        return parts
+
+    queries: list[FaceQuery] = []
+    for rule in grammar.non_terminals():
+        if rule.transparent:
+            continue
+
+        body = rule.fn(grammar)
+        for production in body.flatten(with_metadata=True):
+            queries.extend(scoop(rule.name, production, set()))
+
+    for rule in grammar.terminals():
+        highlight = rule.meta.get("highlight")
+        if isinstance(highlight, parser.HighlightMeta):
+            feature = highlight.font_lock_feature
+            face = highlight.font_lock_face
+            if feature and face:
+                queries.append(
+                    FaceQuery(
+                        node=terminal_name(rule),
+                        field=None,
+                        feature=feature,
+                        face=face,
+                    )
+                )
+
+    # Remove duplicates, which happen.
+    queries = list(set(queries))
+    queries.sort()
+
+    # Group by feature.
+    features = []
+    for feature, qs in itertools.groupby(queries, key=lambda x: x.feature):
+        feature_group = f":language {grammar.name}\n:override t\n:feature {feature}\n"
+
+        face_queries = []
+        for query in qs:
+            if query.field:
+                fq = f"({query.node} {query.field}: _ @{query.face})"
+            else:
+                fq = f"({query.node}) @{query.face}"
+            face_queries.append(fq)
+
+        face_queries_str = "\n ".join(face_queries)
+        feature_group += f"({face_queries_str})\n"
+
+        features.append(feature_group)
+
+    feature_string = "\n".join(features)
+    feature_string = textwrap.indent(feature_string, "    ")
+    feature_string = feature_string.strip()
+
+    feature_string = f"""
+(defvar {grammar.name}-font-lock-rules
+  '({feature_string})
+  "Tree-sitter font lock rules for {grammar.name}.")
+    """.strip()
+
+    return feature_string
+
+
+def emit_emacs_major_mode(grammar: parser.Grammar, path: pathlib.Path | str):
+    face_var = gather_faces(grammar)