Added compilation database support for clang and gcc

This tool is originally from mongodb.

- Updated CPPSUFFIXES to use scons suffixes
- objective-c files will also be loaded into the compilation database where the compiler / tooling is available to compile the files.

Known limitations:

- This will not work with msvc as your compiler.

3 files changed, 189 insertions, 1 deletions

diff --git a/.appveyor.yml b/.appveyor.yml
index 6e124cb265..c39a485d35 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -29,7 +29,9 @@ cache:
 
 install:
   - SET "PATH=%PYTHON%;%PYTHON%\\Scripts;%PATH%"
-  - pip install scons==3.1.2
+  - pip install -U wheel  # needed for pip install scons to work, otherwise a flag is missing
+  - pip install scons # use stable scons
+  - if defined VS call "%VS%" %ARCH%  # if defined - so we can also use mingw
 
 before_build:
   - echo %GD_PLATFORM%
diff --git a/SConstruct b/SConstruct
index 0c91399a12..86014b8160 100644
--- a/SConstruct
+++ b/SConstruct
@@ -272,6 +272,15 @@ if selected_platform in platform_list:
     else:
         env = env_base.Clone()
 
+    # Custom tools are loaded automatically by SCons from site_scons/site_tools,
+    # but we want to use a different folder, so we register it manually.
+    from SCons.Script.Main import _load_site_scons_dir
+
+    _load_site_scons_dir(".", "misc/scons")
+
+    env.Tool("compilation_db")
+    env.Alias("compiledb", env.CompilationDatabase("compile_commands.json"))
+
     if env["dev"]:
         env["verbose"] = True
         env["warnings"] = "extra"
diff --git a/misc/scons/site_tools/compilation_db.py b/misc/scons/site_tools/compilation_db.py
new file mode 100644
index 0000000000..87db32adc9
--- /dev/null
+++ b/misc/scons/site_tools/compilation_db.py
@@ -0,0 +1,177 @@
+# Copyright 2015 MongoDB Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import json
+import SCons
+import itertools
+
+# Implements the ability for SCons to emit a compilation database for the MongoDB project. See
+# http://clang.llvm.org/docs/JSONCompilationDatabase.html for details on what a compilation
+# database is, and why you might want one. The only user visible entry point here is
+# 'env.CompilationDatabase'. This method takes an optional 'target' to name the file that
+# should hold the compilation database, otherwise, the file defaults to compile_commands.json,
+# which is the name that most clang tools search for by default.
+
+# TODO: Is there a better way to do this than this global? Right now this exists so that the
+# emitter we add can record all of the things it emits, so that the scanner for the top level
+# compilation database can access the complete list, and also so that the writer has easy
+# access to write all of the files. But it seems clunky. How can the emitter and the scanner
+# communicate more gracefully?
+__COMPILATION_DB_ENTRIES = []
+
+# We make no effort to avoid rebuilding the entries. Someday, perhaps we could and even
+# integrate with the cache, but there doesn't seem to be much call for it.
+class __CompilationDbNode(SCons.Node.Python.Value):
+    def __init__(self, value):
+        SCons.Node.Python.Value.__init__(self, value)
+        self.Decider(changed_since_last_build_node)
+
+
+def changed_since_last_build_node(child, target, prev_ni, node):
+    """ Dummy decider to force always building"""
+    return True
+
+
+def makeEmitCompilationDbEntry(comstr):
+    """
+    Effectively this creates a lambda function to capture:
+    * command line
+    * source
+    * target
+    :param comstr: unevaluated command line
+    :return: an emitter which has captured the above
+    """
+    user_action = SCons.Action.Action(comstr)
+
+    def EmitCompilationDbEntry(target, source, env):
+        """
+        This emitter will be added to each c/c++ object build to capture the info needed
+        for clang tools
+        :param target: target node(s)
+        :param source: source node(s)
+        :param env: Environment for use building this node
+        :return: target(s), source(s)
+        """
+
+        dbtarget = __CompilationDbNode(source)
+
+        entry = env.__COMPILATIONDB_Entry(
+            target=dbtarget,
+            source=[],
+            __COMPILATIONDB_UTARGET=target,
+            __COMPILATIONDB_USOURCE=source,
+            __COMPILATIONDB_UACTION=user_action,
+            __COMPILATIONDB_ENV=env,
+        )
+
+        # TODO: Technically, these next two lines should not be required: it should be fine to
+        # cache the entries. However, they don't seem to update properly. Since they are quick
+        # to re-generate disable caching and sidestep this problem.
+        env.AlwaysBuild(entry)
+        env.NoCache(entry)
+
+        __COMPILATION_DB_ENTRIES.append(dbtarget)
+
+        return target, source
+
+    return EmitCompilationDbEntry
+
+
+def CompilationDbEntryAction(target, source, env, **kw):
+    """
+    Create a dictionary with evaluated command line, target, source
+    and store that info as an attribute on the target
+    (Which has been stored in __COMPILATION_DB_ENTRIES array
+    :param target: target node(s)
+    :param source: source node(s)
+    :param env: Environment for use building this node
+    :param kw:
+    :return: None
+    """
+
+    command = env["__COMPILATIONDB_UACTION"].strfunction(
+        target=env["__COMPILATIONDB_UTARGET"], source=env["__COMPILATIONDB_USOURCE"], env=env["__COMPILATIONDB_ENV"],
+    )
+
+    entry = {
+        "directory": env.Dir("#").abspath,
+        "command": command,
+        "file": str(env["__COMPILATIONDB_USOURCE"][0]),
+    }
+
+    target[0].write(entry)
+
+
+def WriteCompilationDb(target, source, env):
+    entries = []
+
+    for s in __COMPILATION_DB_ENTRIES:
+        entries.append(s.read())
+
+    with open(str(target[0]), "w") as target_file:
+        json.dump(entries, target_file, sort_keys=True, indent=4, separators=(",", ": "))
+
+
+def ScanCompilationDb(node, env, path):
+    return __COMPILATION_DB_ENTRIES
+
+
+def generate(env, **kwargs):
+
+    static_obj, shared_obj = SCons.Tool.createObjBuilders(env)
+
+    env["COMPILATIONDB_COMSTR"] = kwargs.get("COMPILATIONDB_COMSTR", "Building compilation database $TARGET")
+
+    components_by_suffix = itertools.chain(
+        itertools.product(
+            env["CPPSUFFIXES"],
+            [
+                (static_obj, SCons.Defaults.StaticObjectEmitter, "$CXXCOM"),
+                (shared_obj, SCons.Defaults.SharedObjectEmitter, "$SHCXXCOM"),
+            ],
+        ),
+    )
+
+    for entry in components_by_suffix:
+        suffix = entry[0]
+        builder, base_emitter, command = entry[1]
+
+        # Ensure we have a valid entry
+        # used to auto ignore header files
+        if suffix in builder.emitter:
+            emitter = builder.emitter[suffix]
+            builder.emitter[suffix] = SCons.Builder.ListEmitter([emitter, makeEmitCompilationDbEntry(command),])
+
+    env["BUILDERS"]["__COMPILATIONDB_Entry"] = SCons.Builder.Builder(
+        action=SCons.Action.Action(CompilationDbEntryAction, None),
+    )
+
+    env["BUILDERS"]["__COMPILATIONDB_Database"] = SCons.Builder.Builder(
+        action=SCons.Action.Action(WriteCompilationDb, "$COMPILATIONDB_COMSTR"),
+        target_scanner=SCons.Scanner.Scanner(function=ScanCompilationDb, node_class=None),
+    )
+
+    def CompilationDatabase(env, target):
+        result = env.__COMPILATIONDB_Database(target=target, source=[])
+
+        env.AlwaysBuild(result)
+        env.NoCache(result)
+
+        return result
+
+    env.AddMethod(CompilationDatabase, "CompilationDatabase")
+
+
+def exists(env):
+    return True