Add script to keep .editorconfig in sync with .gitattributes

Our repo already contained an .editorconfig file, but it was not kept
up to date with .gitattributes.  This adds a script that keeps these
files in sync.  A big advantage of the editorconfig file is that it
many editors/IDEs get automatically configured to trim trailing
newlines and add a final newline on save, while .gitattributes only
complains about these problems instead of automatically fixing them.

This also adds rules to .gitattributes for Python files as well as for
C files in pg_bsd_indent directory (which have a different tab_width
than most C files due to being vendored in).

Author: Jelte Fennema-Nio <github-tech@jeltef.nl>
Discussion: https://www.postgresql.org/message-id/flat/CAGECzQQGzbroAXi+Yicp3HvcCo4=g84kaOgjuvQ5MW9F0ubOGg@mail.gmail.com

src/tools/generate_editorconfig.py

@@ -0,0 +1,94 @@
+#!/usr/bin/env python3
+
+import os
+
+
+def cd_to_repo_root():
+    abspath = os.path.abspath(__file__)
+    dname = os.path.join(os.path.dirname(abspath), "..", "..")
+    os.chdir(dname)
+
+
+# Space based indentation levels are not tracked in .gitattributes, so
+# we hardcode them here for the relevant filetypes.
+space_based_indent_sizes = {
+    "*.py": 4,
+    "*.sgml": 1,
+    "*.xsl": 1,
+    "*.xml": 2,
+}
+
+
+def main():
+    cd_to_repo_root()
+
+    with open(".gitattributes", "r") as f:
+        lines = f.read().splitlines()
+
+    new_contents = """root = true
+
+[*]
+indent_size = tab
+"""
+
+    for line in lines:
+        if line.startswith("#") or len(line) == 0:
+            continue
+        name, git_rules = line.split()
+        if git_rules == "-whitespace":
+            rules = [
+                "indent_style = unset",
+                "indent_size = unset",
+                "trim_trailing_whitespace = unset",
+                "insert_final_newline = unset",
+            ]
+        elif git_rules.startswith("whitespace="):
+            git_whitespace_rules = git_rules.replace("whitespace=", "").split(",")
+            rules = []
+            if "-blank-at-eol" in git_whitespace_rules:
+                rules += ["trim_trailing_whitespace = unset"]
+            else:
+                rules += ["trim_trailing_whitespace = true"]
+
+            if "-blank-at-eof" in git_whitespace_rules:
+                rules += ["insert_final_newline = unset"]
+            else:
+                rules += ["insert_final_newline = true"]
+
+            if "tab-in-indent" in git_whitespace_rules:
+                rules += ["indent_style = space"]
+            elif "indent-with-non-tab" in git_whitespace_rules:
+                rules += ["indent_style = tab"]
+            elif name in ["*.pl", "*.pm"]:
+                # We want editors to use tabs for indenting Perl
+                # files, but we cannot add it such a rule to
+                # .gitattributes, because certain lines are still
+                # indented with spaces (e.g. SYNOPSIS blocks).  So we
+                # hardcode the rule here.
+
+                rules += ["indent_style = tab"]
+            else:
+                rules += ["indent_style = unset"]
+
+            tab_width = "unset"
+            for rule in git_whitespace_rules:
+                if rule.startswith("tabwidth="):
+                    tab_width = rule.replace("tabwidth=", "")
+            rules += [f"tab_width = {tab_width}"]
+
+            if name in space_based_indent_sizes:
+                indent_size = space_based_indent_sizes[name]
+                rules += [f"indent_size = {indent_size}"]
+
+        else:
+            continue
+
+        rules = "\n".join(rules)
+        new_contents += f"\n[{name}]\n{rules}\n"
+
+    with open(".editorconfig", "w") as f:
+        f.write(new_contents)
+
+
+if __name__ == "__main__":
+    main()