servo: Merge #14025 - Add --with-debug-assertions flag for Mach (from iamrohit7:debug-assertions); r=Wafflespeanut

I tested out building a release with the flag and added a `debug_assert!(false)` in `fn main` and it panicked.
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #14009  (github issue number if applicable).

<!-- Either: -->
- [ ] There are tests for these changes OR
- [X] These changes do not require tests because they are manually tested

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Source-Repo: https://github.com/servo/servo
Source-Revision: dbce416ad436b9a3a007181fbd5d0f158cd7d9e4

servo/etc/ci/buildbot_steps.yml

@@ -55,15 +55,15 @@ linux-dev:
   - bash ./etc/ci/check_no_panic.sh
 
 linux-rel-wpt:
-  - ./mach build --release
+  - ./mach build --release --with-debug-assertions
   - ./mach test-wpt-failure
   - ./mach test-wpt --release --processes 24 --log-raw test-wpt.log --log-errorsummary wpt-errorsummary.log
   - ./mach test-wpt --release --binary-arg=--multiprocess --processes 24 --log-raw test-wpt-mp.log --log-errorsummary wpt-mp-errorsummary.log eventsource
 
 linux-rel-css:
-  - ./mach build --release
+  - ./mach build --release --with-debug-assertions
   - ./mach test-css --release --processes 16 --log-raw test-css.log --log-errorsummary css-errorsummary.log
-  - ./mach build-cef --release
+  - ./mach build-cef --release --with-debug-assertions
   - ./mach build-geckolib --release
   - ./mach test-stylo --release
   - bash ./etc/ci/lockfile_changed.sh

servo/python/servo/build_commands.py

@@ -153,8 +153,13 @@ class MachCommands(CommandBase):
                      help='Print verbose output')
     @CommandArgument('params', nargs='...',
                      help="Command-line arguments to be passed through to Cargo")
+    @CommandArgument('--with-debug-assertions',
+                     default=None,
+                     action='store_true',
+                     help='Enable debug assertions in release')
     def build(self, target=None, release=False, dev=False, jobs=None,
-              features=None, android=None, verbose=False, debug_mozjs=False, params=None):
+              features=None, android=None, verbose=False, debug_mozjs=False, params=None,
+              with_debug_assertions=False):
         if android is None:
             android = self.config["build"]["android"]
         features = features or self.servo_features()
@@ -217,10 +222,7 @@ class MachCommands(CommandBase):
         build_start = time()
         env = self.build_env(target=target, is_build=True)
 
-        # TODO: If this ends up making it, we should probably add a
-        # --release-with-debug-assertions option or similar, so it's easier to
-        # build locally.
-        if env.get("SERVO_ENABLE_DEBUG_ASSERTIONS", None):
+        if with_debug_assertions:
             env["RUSTFLAGS"] = "-C debug_assertions"
 
         if android:
@@ -339,7 +341,12 @@ class MachCommands(CommandBase):
     @CommandArgument('--release', '-r',
                      action='store_true',
                      help='Build in release mode')
-    def build_cef(self, jobs=None, verbose=False, release=False):
+    @CommandArgument('--with-debug-assertions',
+                     default=None,
+                     action='store_true',
+                     help='Enable debug assertions in release')
+    def build_cef(self, jobs=None, verbose=False, release=False,
+                  with_debug_assertions=False):
         self.ensure_bootstrapped()
 
         ret = None
@@ -358,10 +365,7 @@ class MachCommands(CommandBase):
         build_start = time()
         env = self.build_env(is_build=True)
 
-        # TODO: If this ends up making it, we should probably add a
-        # --release-with-debug-assertions option or similar, so it's easier to
-        # build locally.
-        if env.get("SERVO_ENABLE_DEBUG_ASSERTIONS", None):
+        if with_debug_assertions:
             env["RUSTFLAGS"] = "-C debug_assertions"
 
         with cd(path.join("ports", "cef")):