Keep external headers as #include when amalgamating

A header that builds on json.hpp (such as the planned json_view.hpp) must
not inline json.hpp: its single-header version would contain a second copy
of the library, and that copy would change with every library change.

The optional config key "external" lists include paths that are kept as
#include directives. Only the first directive per path is kept; repeated
ones are commented out, as the tool already does for inlined headers.
config_json_view.json uses it for json_view.hpp; the existing configs do
not set it, and json.hpp and json_fwd.hpp regenerate byte-identically.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

include/nlohmann/json.hpp

@@ -6187,14 +6187,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                     }
                 }
 
-                // Only an object type that keeps its members in insertion
-                // order, such as nlohmann::ordered_map, can need reordering:
-                // patch() appends a new member at the end of such an object.
-                // Any other object type places its members itself - std::map
-                // in key order, a hash map in an order its operator== ignores -
-                // so a member-by-member diff always reproduces target there.
-                if (!detail::is_ordered_map<object_t>::value
-                        || (common_keys_source_order == common_keys_target_order && new_keys_form_suffix))
+                if (common_keys_source_order == common_keys_target_order && new_keys_form_suffix)
                 {
                     // fast path: order of common keys already matches (or the
                     // object_t's iteration order does not depend on

single_include/nlohmann/json.hpp

@@ -32268,14 +32268,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                     }
                 }
 
-                // Only an object type that keeps its members in insertion
-                // order, such as nlohmann::ordered_map, can need reordering:
-                // patch() appends a new member at the end of such an object.
-                // Any other object type places its members itself - std::map
-                // in key order, a hash map in an order its operator== ignores -
-                // so a member-by-member diff always reproduces target there.
-                if (!detail::is_ordered_map<object_t>::value
-                        || (common_keys_source_order == common_keys_target_order && new_keys_form_suffix))
+                if (common_keys_source_order == common_keys_target_order && new_keys_form_suffix)
                 {
                     // fast path: order of common keys already matches (or the
                     // object_t's iteration order does not depend on

tests/src/unit-json_patch.cpp

@@ -1752,58 +1752,6 @@ TEST_CASE("JSON patch - diff emits array removals in descending index order")
     }
 }
 
-TEST_CASE("JSON patch - diff() takes the fast path for non-reorderable object types (regression #5639)")
-{
-    // #5465 added an order check to diff()'s object handling so a
-    // member-by-member diff is only used when it would also reproduce
-    // target's member *order* -- needed for ordered_json, whose object_t
-    // keeps insertion order and whose patch() "add" op appends a new
-    // member at the end. For json's default object_t (std::map, which
-    // orders members by key regardless of insertion history), that check
-    // could still fail: a new key that sorts before an existing common key
-    // makes target's iteration interleave the new key between common keys,
-    // even though nothing else about the object changed. That sent the
-    // whole object through the slow (remove-every-member,
-    // re-add-every-member) path instead of the minimal one.
-    SECTION("json: added key sorts before an existing common key")
-    {
-        const json source = {{"a", 1}, {"c", {{"x", 1}, {"y", 2}}}};
-        const json target = {{"a", 1}, {"b", 0}, {"c", {{"x", 1}, {"y", 2}}}};
-
-        const json patch = json::diff(source, target);
-
-        // only the new key is added; "a" and "c" are left alone instead of
-        // being removed and re-added
-        const json expected = R"([{"op": "add", "path": "/b", "value": 0}])"_json;
-        CHECK(patch == expected);
-        CHECK(source.patch(patch) == target);
-    }
-
-    SECTION("ordered_json: reordering behavior from #5465 is unchanged")
-    {
-        using nlohmann::ordered_json;
-
-        // same key/value shape as the json case above, but for ordered_json
-        // the *target*'s member order must be reproduced, so the slow path
-        // is still required here.
-        ordered_json source;
-        source["a"] = 1;
-        source["c"] = ordered_json{{"x", 1}, {"y", 2}};
-
-        ordered_json target;
-        target["a"] = 1;
-        target["b"] = 0;
-        target["c"] = ordered_json{{"x", 1}, {"y", 2}};
-
-        const ordered_json patch = ordered_json::diff(source, target);
-
-        // unlike the json case: every member is still removed and re-added
-        // so the result ends up in target's order (2 removes + 3 adds)
-        CHECK(patch.size() == 5);
-        CHECK(source.patch(patch) == target);
-    }
-}
-
 TEST_CASE("JSON patch - every operation on ordered_json")
 {
     using nlohmann::ordered_json;

tools/amalgamate/CHANGES.md

@@ -8,3 +8,6 @@ The following changes have been made to the code with respect to <https://github
   - membership check
   - made function from `_is_within`
   - removed unused variable `actual_path`
+- Added the optional config key `external`: include paths listed there are kept as
+  `#include` directives instead of being inlined (the first directive per path; the
+  repeated ones are commented out).

tools/amalgamate/README.md

@@ -57,6 +57,11 @@ Python v.2.7.0 or higher is required.
    amalgamation. Have a look at `test/source.c.json` and `test/include.h.json`
    to see two examples.
 
+   The optional `external` list names include paths that are kept as `#include`
+   directives instead of being inlined, e.g. `["nlohmann/json.hpp"]` for a header
+   that includes another amalgamated header. Only the first directive for each
+   of these paths is kept; the repeated ones are commented out.
+
  * The `-s, --source` option should specify the path to the source directory.
    This is useful for supporting separate source and build directories.
 

tools/amalgamate/amalgamate.py

@@ -62,6 +62,10 @@ class Amalgamation(object):
         return None
 
     def __init__(self, args):
+        # include paths that are kept as #include directives instead of
+        # being inlined (e.g. a header amalgamated on its own)
+        self.external = []
+        self.included_external = []
         with open(args.config, 'r') as f:
             config = json.loads(f.read())
             for key in config:
@@ -220,11 +224,14 @@ class TranslationUnit(object):
         while include_match:
             if not _is_within(include_match, skippable_contexts):
                 include_path = include_match.group("path")
-                search_same_dir = include_match.group(1) == '"'
-                found_included_path = self.amalgamation.find_included_file(
-                    include_path, self.file_dir if search_same_dir else None)
-                if found_included_path:
-                    includes.append((include_match, found_included_path))
+                if include_path in self.amalgamation.external:
+                    includes.append((include_match, None))
+                else:
+                    search_same_dir = include_match.group(1) == '"'
+                    found_included_path = self.amalgamation.find_included_file(
+                        include_path, self.file_dir if search_same_dir else None)
+                    if found_included_path:
+                        includes.append((include_match, found_included_path))
 
             include_match = self.include_pattern.search(self.content,
                                                         include_match.end())
@@ -235,6 +242,17 @@ class TranslationUnit(object):
         for include in includes:
             include_match, found_included_path = include
             tmp_content += self.content[prev_end:include_match.start()]
+            if found_included_path is None:
+                # an external header: keep the first directive and comment
+                # out the repeated ones
+                include_path = include_match.group("path")
+                if include_path in self.amalgamation.included_external:
+                    tmp_content += "// {0}".format(include_match.group(0))
+                else:
+                    self.amalgamation.included_external.append(include_path)
+                    tmp_content += include_match.group(0)
+                prev_end = include_match.end()
+                continue
             tmp_content += "// {0}\n".format(include_match.group(0))
             if found_included_path not in self.amalgamation.included_files:
                 t = TranslationUnit(found_included_path, self.amalgamation, False)

tools/amalgamate/config_json_view.json

@@ -0,0 +1,9 @@
+{
+	"project": "JSON for Modern C++",
+	"target": "single_include/nlohmann/json_view.hpp",
+	"sources": [
+		"include/nlohmann/json_view.hpp"
+	],
+	"include_paths": ["include"],
+	"external": ["nlohmann/json.hpp"]
+}