Drop support for bazel5; switch to all bzlmod.

bazel5 is EOL in 2 months. bazel6 and beyond all support bzlmod,
which means we can remove duplicate dependencies in WORKSPACE
and MODULE.bazel.

.bazelrc

@@ -1,3 +1,6 @@
+# bazel < 7 needs explicit enabling of bzlmod dependencies.
+build --enable_bzlmod
+
 # Enable support for absl types like string_view in gtest.
 build --define="absl=1"
 
@@ -26,6 +29,23 @@ common:macos --features=-supports_dynamic_linker --linkopt=-framework --linkopt=
 # Since we use designated initializers (C99 ... but >= c++20), compiler really wants the c++20 mode
 common:windows --compiler=clang-cl --cxxopt=/std:c++20 --host_cxxopt=/std:c++20 --client_env=BAZEL_CXXOPTS=/std:c++20
 
+# Turn warnings on...
+build --copt "-Wall"                   --host_copt "-Wall"
+build --copt "-Wextra"                 --host_copt "-Wextra"
+
+# ... and disable the warnings we're not interested in.
+build --copt "-Wno-sign-compare"       --host_copt "-Wno-sign-compare"
+build --copt "-Wno-unused-parameter"   --host_copt "-Wno-unused-parameter"
+build --copt "-Wno-missing-field-initializers" --host_copt "-Wno-missing-field-initializers"
+
+# TODO: The code around this warning looks benign, but should be investigated
+build --cxxopt "-Wno-dangling-reference"   --host_cxxopt "-Wno-dangling-reference"
+
+# For 3rd party code: Disable warnings entirely.
+# They are not actionable and just create noise.
+build --per_file_copt=external/.*@-w
+build --host_per_file_copt=external/.*@-w
+
 # Address sanitizer settings.
 build:asan --strip=never
 build:asan --copt -fsanitize=address

.github/bin/run-clang-format.sh

@@ -32,7 +32,7 @@ find . -name "*.h" -o -name "*.cc" \
 # If we have buildifier installed, use that on BUILD files
 if command -v ${BUILDIFIER} >/dev/null; then
   echo "Run $(buildifier --version)"
-  ${BUILDIFIER} -lint=fix WORKSPACE MODULE.bazel $(find . -name BUILD -o -name "*.bzl")
+  ${BUILDIFIER} -lint=fix MODULE.bazel $(find . -name BUILD -o -name "*.bzl")
 fi
 
 # Check if we got any diff

.github/settings.sh

@@ -32,7 +32,7 @@ export BAZEL_CXXOPTS="-std=c++17"
 export BAZEL_OPTS="-c opt --noshow_progress"
 
 # Used to fetch the BAZEL version where needed.
-export BAZEL_VERSION=5.4.1
+export BAZEL_VERSION=6.5.0
 
 # Kythe version for extracting xRefs
 export KYTHE_VERSION=v0.0.52

.github/workflows/verible-ci.yml

@@ -103,8 +103,8 @@ jobs:
         path: |
           /root/.cache/clang-tidy
           /root/.cache/bazel
-        key: clang-tidy-${{ steps.cache_timestamp.outputs.time }}
-        restore-keys: clang-tidy-
+        key: clang-tidy1-${{ steps.cache_timestamp.outputs.time }}
+        restore-keys: clang-tidy1-
 
     - name: Build Project genrules
       run: |
@@ -238,8 +238,8 @@ jobs:
       if: matrix.mode != 'clean' && matrix.mode != 'coverage'
       with:
         path: "/root/.cache/bazel"
-        key: bazelcache3_${{ matrix.arch }}_${{ matrix.mode }}_${{ steps.cache_timestamp.outputs.time }}
-        restore-keys: bazelcache3_${{ matrix.arch }}_${{ matrix.mode }}_
+        key: bazelcache_${{ matrix.arch }}_${{ matrix.mode }}_${{ steps.cache_timestamp.outputs.time }}
+        restore-keys: bazelcache_${{ matrix.arch }}_${{ matrix.mode }}_
 
     - name: Install Dependencies
       run: |
@@ -397,8 +397,8 @@ jobs:
       with:
         path: |
           /private/var/tmp/_bazel_runner
-        key: bazelcache_macos_${{ steps.cache_timestamp.outputs.time }}
-        restore-keys: bazelcache_macos_
+        key: bazelcache_macos1_${{ steps.cache_timestamp.outputs.time }}
+        restore-keys: bazelcache_macos1_
 
     - name: Tests
       # MacOS has a broken patch utility:
@@ -451,7 +451,7 @@ jobs:
       uses: actions/cache@v3
       with:
         path: "c:/users/runneradmin/_bazel_runneradmin"
-        key: bazelcache_windows_${{ steps.cache_timestamp.outputs.time }}
+        key: bazelcache_windows1_${{ steps.cache_timestamp.outputs.time }}
         restore-keys: bazelcache_windows_
 
     - name: Install dependencies