add --incompatible_strict_action_env

I kept running into a problem where bazel would rebuild every time I changed from being in a python virtualenv to not doing that (which happens because I was using the python scripts). I found out this is because PATH changes cause a full rebuild. This flag avoids that.

PiperOrigin-RevId: 626403108

.bazelrc

@@ -5,5 +5,9 @@ common --action_env=BAZEL_CXXOPTS=-std=gnu++17
 common --cxxopt='-std=gnu++17'
 common --copt=-fdiagnostics-color=always
 common --test_output=errors
+# compilation_mode options below are `dbg` (debug symbols) `fastbuild`
+# (build as quickly as possible), and `opt` (turn on all optimizations)
 common -c dbg
 common --noenable_bzlmod
+# prevents changes to PATH from causing a full rebuild
+common --incompatible_strict_action_env

.github/workflows/build_and_test.yml

@@ -60,13 +60,17 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-bazel-${{ hashFiles('.bazelversion', '.bazelrc', 'WORKSPACE') }}-
 
+      # --noincompatible_strict_action_env is used below to inherit the path
+      # from the parent process, which is required for the build to be cached
+      # and reused in the `Test rust codegen targets` step below, as that step
+      # requires the `PATH` to find the `cargo` binary.
       - name: "Run `bazel build`"
         run: |
-          bazel build -c fastbuild //...
+          bazel build --noincompatible_strict_action_env  -c fastbuild //...
 
       - name: "Run `bazel test`"
         run: |
-          bazel test -c fastbuild //...
+          bazel test --noincompatible_strict_action_env -c fastbuild //...
 
       # Tests specifically for the tfhe-rs codegen
       - name: rustup toolchain install

.github/workflows/run_rust_tests.sh

@@ -3,4 +3,13 @@
 set -eux
 set -o pipefail
 
-bazel query "filter('.mlir.test$', //tests/tfhe_rust/end_to_end/...)" | xargs bazel test -c fastbuild --sandbox_writable_path=$HOME/.cargo "$@"
+# noincompatible_strict_action_env is used to inherit the PATH environment
+# variable from the parent process, which is needed to find the `cargo`
+# executable.
+
+bazel query "filter('.mlir.test$', //tests/tfhe_rust/end_to_end/...)" \
+| xargs bazel test \
+--noincompatible_strict_action_env \
+-c fastbuild \
+--sandbox_writable_path=$HOME/.cargo \
+"$@"

docs/content/en/docs/ide_configuration.md

@@ -45,3 +45,23 @@ file changes.
 If you encounter errors like `*.h.inc` not found, or syntax errors inside these
 files, you may need to build those targets and then re-run the `refresh_all`
 command above.
+
+## Tips for working with Bazel
+
+Bazel is notoriously fickle when it comes to deciding whether a full rebuild is
+necessary, which is bad for HEIR because rebuilding LLVM from scratch takes 15
+minutes or more.
+
+The main things that cause a rebuild are:
+
+-   A change to the command-line flags passed to bazel, e.g., `-c opt` vs `-c
+    dbg` for optimization level and debug symbols.
+-   A change to the `.bazelrc` that implicitly causes a flag change. Note HEIR
+    has its own project-specific `.bazelrc` in the root directory.
+-   A change to relevant command-line variables, such as `PATH`, which is
+    avoided by the `incompatible_strict_action_env` flag. Note activating a
+    python virtualenv triggers a `PATH` change.
+
+Bazel compilation flags are set by default in the project root's `.bazelrc` in
+such a way as to avoid rebuilds during development as much as possible. This
+includes setting `-c dbg` and `--incompatible_strict_action_env`.