[libc] Make template_header optional for hdrgen

libc/include/ctype.yaml

@@ -1,8 +1,6 @@
 header: ctype.h
-header_template: ctype.h.def
-macros: []
-types:
-  - type_name: locale_t
+standards:
+  - stdc
 enums: []
 objects: []
 functions:
@@ -104,98 +102,98 @@ functions:
       - type: int
   - name: isalnum_l
     standards:
-      - stdc
+      - posix
     return_type: int
     arguments:
       - type: int
       - type: locale_t
   - name: isalpha_l
     standards:
-      - stdc
+      - posix
     return_type: int
     arguments:
       - type: int
       - type: locale_t
   - name: isblank_l
     standards:
-      - stdc
+      - posix
     return_type: int
     arguments:
       - type: int
       - type: locale_t
   - name: iscntrl_l
     standards:
-      - stdc
+      - posix
     return_type: int
     arguments:
       - type: int
       - type: locale_t
   - name: isdigit_l
     standards:
-      - stdc
+      - posix
     return_type: int
     arguments:
       - type: int
       - type: locale_t
   - name: isgraph_l
     standards:
-      - stdc
+      - posix
     return_type: int
     arguments:
       - type: int
       - type: locale_t
   - name: islower_l
     standards:
-      - stdc
+      - posix
     return_type: int
     arguments:
       - type: int
       - type: locale_t
   - name: isprint_l
     standards:
-      - stdc
+      - posix
     return_type: int
     arguments:
       - type: int
       - type: locale_t
   - name: ispunct_l
     standards:
-      - stdc
+      - posix
     return_type: int
     arguments:
       - type: int
       - type: locale_t
   - name: isspace_l
     standards:
-      - stdc
+      - posix
     return_type: int
     arguments:
       - type: int
       - type: locale_t
   - name: isupper_l
     standards:
-      - stdc
+      - posix
     return_type: int
     arguments:
       - type: int
       - type: locale_t
   - name: isxdigit_l
     standards:
-      - stdc
+      - posix
     return_type: int
     arguments:
       - type: int
       - type: locale_t
   - name: tolower_l
     standards:
-      - stdc
+      - posix
     return_type: int
     arguments:
       - type: int
       - type: locale_t
   - name: toupper_l
     standards:
-      - stdc
+      - posix
     return_type: int
     arguments:
       - type: int

libc/utils/hdrgen/header.py

@@ -6,6 +6,7 @@
 #
 # ==-------------------------------------------------------------------------==#
 
+import re
 from functools import reduce
 from pathlib import PurePosixPath
 
@@ -30,6 +31,37 @@
 COMPILER_HEADER_TYPES.update({f"int{size}_t": "<stdint.h>" for size in STDINT_SIZES})
 COMPILER_HEADER_TYPES.update({f"uint{size}_t": "<stdint.h>" for size in STDINT_SIZES})
 
+NONIDENTIFIER = re.compile("[^a-zA-Z0-9_]+")
+
+COMMON_HEADER = PurePosixPath("__llvm-libc-common.h")
+
+# All the canonical identifiers are in lowercase for easy maintenance.
+# This maps them to the pretty descriptions to generate in header comments.
+LIBRARY_DESCRIPTIONS = {
+    "stdc": "Standard C",
+    "posix": "POSIX",
+    "bsd": "BSD",
+    "gnu": "GNU",
+    "linux": "Linux",
+}
+
+HEADER_TEMPLATE = """\
+//===-- {library} header <{header}> --===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===---------------------------------------------------------------------===//
+
+#ifndef {guard}
+#define {guard}
+
+%%public_api()
+
+#endif // {guard}
+"""
+
 
 class HeaderFile:
     def __init__(self, name):
@@ -40,6 +72,7 @@ def __init__(self, name):
         self.enumerations = []
         self.objects = []
         self.functions = []
+        self.standards = []
 
     def add_macro(self, macro):
         self.macros.append(macro)
@@ -63,6 +96,13 @@ def all_types(self):
             set(self.types),
         )
 
+    def all_standards(self):
+        # FIXME: Only functions have the "standard" field, but all the entity
+        # types should have one too.
+        return set(self.standards).union(
+            *(filter(None, (f.standards for f in self.functions)))
+        )
+
     def includes(self):
         return {
             PurePosixPath("llvm-libc-macros") / macro.header
@@ -75,14 +115,62 @@ def includes(self):
             for typ in self.all_types()
         }
 
+    def header_guard(self):
+        return "LLVM_LIBC_" + "_".join(
+            word.upper() for word in NONIDENTIFIER.split(self.name) if word
+        )
+
+    def library_description(self):
+        # If the header itself is in standard C, just call it that.
+        if "stdc" in self.standards:
+            return LIBRARY_DESCRIPTIONS["stdc"]
+        # If the header itself is in POSIX, just call it that.
+        if "posix" in self.standards:
+            return LIBRARY_DESCRIPTIONS["posix"]
+        # Otherwise, consider the standards for each symbol as well.
+        standards = self.all_standards()
+        # Otherwise, it's described by all those that apply, but ignoring
+        # "stdc" and "posix" since this is not a "stdc" or "posix" header.
+        return " / ".join(
+            sorted(
+                LIBRARY_DESCRIPTIONS[standard]
+                for standard in standards
+                if standard not in {"stdc", "posix"}
+            )
+        )
+
+    def template(self, dir, files_read):
+        if self.template_file is not None:
+            # There's a custom template file, so just read it in and record
+            # that it was read as an input file.
+            template_path = dir / self.template_file
+            files_read.add(template_path)
+            return template_path.read_text()
+
+        # Generate the default template.
+        return HEADER_TEMPLATE.format(
+            library=self.library_description(),
+            header=self.name,
+            guard=self.header_guard(),
+        )
+
     def public_api(self):
         # Python 3.12 has .relative_to(dir, walk_up=True) for this.
         path_prefix = PurePosixPath("../" * (len(PurePosixPath(self.name).parents) - 1))
 
         def relpath(file):
             return path_prefix / file
 
-        content = [
+        content = []
+
+        if self.template_file is None:
+            # This always goes before all the other includes, which are sorted.
+            # It's implicitly emitted here when using the default template so
+            # it can get the right relative path.  Custom template files should
+            # all have it explicitly with their right particular relative path.
+            content.append('#include "{file!s}"'.format(file=relpath(COMMON_HEADER)))
+
+        content += [
             f"#include {file}"
             for file in sorted(
                 file if isinstance(file, str) else f'"{relpath(file)!s}"'

libc/utils/hdrgen/main.py

@@ -65,16 +65,10 @@ def write_depfile():
 
     header = load_yaml_file(yaml_file, HeaderFile, args.entry_point)
 
-    if not header.template_file:
-        print(f"{yaml_file}: Missing header_template", sys.stderr)
-        return 2
-
     # The header_template path is relative to the containing YAML file.
-    template_path = yaml_file.parent / header.template_file
+    template = header.template(yaml_file.parent, files_read)
 
-    files_read.add(template_path)
-    with open(template_path) as template:
-        contents = fill_public_api(header.public_api(), template.read())
+    contents = fill_public_api(header.public_api(), template)
 
     write_depfile()
 

libc/utils/hdrgen/tests/expected_output/subdir/test.h

@@ -1,23 +1,24 @@
-//===-- C standard library header subdir/test.h --------------------------===//
+//===-- BSD / GNU header <subdir/test.h> --===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-//===--------------------------------------------------------------------===//
+//===---------------------------------------------------------------------===//
 
 #ifndef LLVM_LIBC_SUBDIR_TEST_H
 #define LLVM_LIBC_SUBDIR_TEST_H
 
 #include "../__llvm-libc-common.h"
-
 #include "../llvm-libc-types/type_a.h"
 #include "../llvm-libc-types/type_b.h"
 
 __BEGIN_C_DECLS
 
 type_a func(type_b) __NOEXCEPT;
 
+void gnufunc(type_a) __NOEXCEPT;
+
 __END_C_DECLS
 
 #endif // LLVM_LIBC_SUBDIR_TEST_H

libc/utils/hdrgen/tests/input/subdir/test.yaml

@@ -1,9 +1,14 @@
 header: subdir/test.h
-header_template: test.h.def
+standards:
+  - bsd
 functions:
   - name: func
     return_type: type_a
     arguments:
       - type: type_b
+  - name: gnufunc
+    return_type: void
+    arguments:
+      - type: type_a
     standards:
-      - stdc
+      - gnu

libc/utils/hdrgen/yaml_to_classes.py

@@ -36,6 +36,7 @@ def yaml_to_classes(yaml_data, header_class, entry_points=None):
     header_name = yaml_data.get("header")
     header = header_class(header_name)
     header.template_file = yaml_data.get("header_template")
+    header.standards = yaml_data.get("standards", [])
 
     for macro_data in yaml_data.get("macros", []):
         header.add_macro(