add basic support for compile_commands.json generation

.clangd

diff --git a/.clangd b/.clangd
new file mode 100644
index 0000000..c3c7e2d
--- /dev/null
+++ b/.clangd
@@ -0,0 +1,15 @@
+---
+If:
+  PathMatch: .*stacktrace.*-inl\.h
+Diagnostics:
+  Suppress: '*'
+---
+If:
+  PathMatch: .*spinlock.*-inl\.h
+Diagnostics:
+  Suppress: '*'
+---
+Diagnostics:
+  Includes:
+    IgnoreHeader:
+      - config\.h

.gitignore

diff --git a/.gitignore b/.gitignore
index de3f9de..e8711a6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -31,6 +31,7 @@
 /cleanup_test
 /cleanup_test.exe
 /compile
+/compile_commands.json
 /config.guess
 /config.log
 /config.status

gen_compile_commands.rb

diff --git a/gen_compile_commands.rb b/gen_compile_commands.rb
new file mode 100755
index 0000000..cae9076
--- /dev/null
+++ b/gen_compile_commands.rb
@@ -0,0 +1,75 @@
+#!/usr/bin/ruby
+
+# Use this script to produce compile_commands.json useful to feed
+# clangd/ccls. Helpful for modern IDEs.
+
+require 'json'
+
+DIRNAME = File.dirname(__FILE__)
+Dir.chdir(DIRNAME)
+
+all_files = Dir['**/*.h'] + Dir['**/*.c'] + Dir['**/*.cc']
+all_files.sort!
+
+def classify(path)
+  return :skip if path =~ /\/googletest\/.*\/test\//
+  return :skip if path == "src/config.h"
+
+  return :skip if path =~ /gmock/
+  return :skip if path =~ /\/googletest\/samples\//
+  return :skip if path.end_with?("/gtest-all.cc")
+
+  return :skip if path.start_with?("src/windows/")
+  return :skip if path.start_with?("vsprojects/")
+
+  if path =~ /libbacktrace(\/|-)/
+    return :default if path.end_with?(".cc")
+    return :libbacktrace
+  end
+
+  :default
+end
+
+NORMAL_INCLUDES = %w[
+  benchmark/ generic-config/ src/gperftools/
+  src/base/ src/
+  vendor/googletest/googletest/include/
+  vendor/googletest/googletest/
+].map {|d| "-I#{d}"}
+
+entries = all_files.map do |filename|
+  args = case classify(filename)
+         when :default
+           # various libc_override_xyz headers
+           # (e.g. libc_override_glibc.h) are not standalone, but we
+           # can make clangd "compile" them by including
+           # src/libc_override.h but setting up this "inclusion" to
+           # skip actual override includes. Yes, ugly. But it works,
+           # mostly.
+           maybe_libc_override = if filename =~ /libc_override_/
+                                   %w[-include src/libc_override.h -DTCMALLOC_SKIP_OVERRIDE]
+                                 else
+                                   []
+                                 end
+           ["clang++", "-x", "c++", "-std=c++17",
+            "-DENABLE_EMERGENCY_MALLOC",
+            *NORMAL_INCLUDES,
+            *maybe_libc_override,
+            "--", filename]
+         when :libbacktrace
+           ["clang",
+            "-Ivendor/libbacktrace-integration",
+            "-Ivendor/libbacktrace",
+            "--", filename]
+         when :skip
+           next
+         end
+  {file: filename,
+   directory: Dir.pwd,
+   arguments: args}
+end.compact
+
+File.open("compile_commands.json", "w") do |f|
+  f.puts JSON.pretty_generate(entries)
+end
+puts "produced #{File.join(DIRNAME, "compile_commands.json")}"