Merge pull request #57806 from akien-mga/scons-gotta-go-fast

SConstruct

@@ -179,9 +179,10 @@ opts.Add(BoolVariable("use_volk", "Use the volk library to load the Vulkan loade
 
 # Advanced options
 opts.Add(BoolVariable("dev", "If yes, alias for verbose=yes warnings=extra werror=yes", False))
-opts.Add(BoolVariable("progress", "Show a progress indicator during compilation", True))
 opts.Add(BoolVariable("tests", "Build the unit tests", False))
+opts.Add(BoolVariable("fast_unsafe", "Enable unsafe options for faster rebuilds", False))
 opts.Add(BoolVariable("verbose", "Enable verbose output for the compilation", False))
+opts.Add(BoolVariable("progress", "Show a progress indicator during compilation", True))
 opts.Add(EnumVariable("warnings", "Level of compilation warnings", "all", ("extra", "all", "moderate", "no")))
 opts.Add(BoolVariable("werror", "Treat compiler warnings as errors", False))
 opts.Add("extra_suffix", "Custom extra suffix added to the base filename of all generated binary files", "")
@@ -360,6 +361,17 @@ if env_base["target"] == "debug":
     # working on the engine itself.
     env_base.Append(CPPDEFINES=["DEV_ENABLED"])
 
+# SCons speed optimization controlled by the `fast_unsafe` option, which provide
+# more than 10 s speed up for incremental rebuilds.
+# Unsafe as they reduce the certainty of rebuilding all changed files, so it's
+# enabled by default for `debug` builds, and can be overridden from command line.
+# Ref: https://github.com/SCons/scons/wiki/GoFastButton
+if methods.get_cmdline_bool("fast_unsafe", env_base["target"] == "debug"):
+    # Renamed to `content-timestamp` in SCons >= 4.2, keeping MD5 for compat.
+    env_base.Decider("MD5-timestamp")
+    env_base.SetOption("implicit_cache", 1)
+    env_base.SetOption("max_drift", 60)
+
 if env_base["use_precise_math_checks"]:
     env_base.Append(CPPDEFINES=["PRECISE_MATH_CHECKS"])