Replace qiskit metapackage with qiskit-terra

This commit completely removes the concept of the `qiskit-terra` package
from Qiskit main.  The hitherto metapackage `qiskit` is promoted to be
the concrete code package.

This is a completely breaking change for packaging purposes for users,
as there is no clean upgrade path from `qiskit-terra` to `qiskit`; PyPI
and pip do not give us the tools to mark that the former obsoletes and
supersedes the latter.  We intend to follow this PR with a technical
blog post somewhere explaining the changes, how users should adapt
("to install Qiskit 1.0, you must start a new venv"), and why we needed
to do this.

The "why", in part, is:

- the metapackage legacy causes awkward upgrade paths on every release;
  some packages still depend on `qiskit-terra`, some on `qiskit`, and
  pip will happily make those two get out-of-sync when upgrading a
  transitive dependency with only a warning that users are used to
  ignoring.

- with the 1.0 release, we (believe we) will have some leeway from users
  to make such a breaking change.

- having the metapackage split makes it difficult for downstream
  projects and developers to test against `main` - they always must
  install both `qiskit-terra` and `qiskit`, and the latter has no
  meaning in editable installs, so needs re-installing after each
  version bump.  Problems surrounding this have already broken CI for
  Qiskit, for at least one internal IBM repo, and at least my dev
  install of Qiskit.  This could be improved a bit with more education,
  but it's still always going to increase the barrier to entry and make
  it much harder to do the right thing.

We will not publish any 1.0 or above version of `qiskit-terra`.  All
dependents on Qiskit should switch their requirements to `qiskit`.

.azure/lint-linux.yml

@@ -26,7 +26,6 @@ jobs:
             -c constraints.txt \
             -r requirements.txt \
             -r requirements-dev.txt \
-            ./qiskit_pkg \
             -e .
           # Build and install both qiskit and qiskit-terra so that any optionals
           # depending on `qiskit` will resolve correctly.
@@ -38,7 +37,7 @@ jobs:
           set -e
           source test-job/bin/activate
           echo "Running black, any errors reported can be fixed with 'tox -eblack'"
-          black --check qiskit test tools examples setup.py qiskit_pkg
+          black --check qiskit test tools examples setup.py
           echo "Running rustfmt check, any errors reported can be fixed with 'cargo fmt'"
           cargo fmt --check
         displayName: "Formatting"
@@ -47,7 +46,7 @@ jobs:
           set -e
           source test-job/bin/activate
           echo "Running ruff"
-          ruff qiskit test tools examples setup.py qiskit_pkg/setup.py
+          ruff qiskit test tools examples setup.py
           echo "Running pylint"
           pylint -rn qiskit test tools
           echo "Running Cargo Clippy"

.azure/test-linux.yml

@@ -74,12 +74,11 @@ jobs:
             python -m pip install -U pip
             python -m pip install -U build
             python -m build --sdist .
-            python -m build --sdist qiskit_pkg
             python -m pip install -U \
               -c constraints.txt \
               -r requirements.txt \
               -r requirements-dev.txt \
-              dist/qiskit*.tar.gz
+              dist/qiskit-*.tar.gz
             # Build and install both qiskit and qiskit-terra so that any optionals
             # depending on `qiskit` will resolve correctly.
           displayName: "Install Terra from sdist"
@@ -92,7 +91,6 @@ jobs:
               -c constraints.txt \
               -r requirements.txt \
               -r requirements-dev.txt \
-              ./qiskit_pkg \
               -e .
             # Build and install both qiskit and qiskit-terra so that any optionals
             # depending on `qiskit` will resolve correctly.

.azure/test-macos.yml

@@ -43,7 +43,6 @@ jobs:
             -c constraints.txt \
             -r requirements.txt \
             -r requirements-dev.txt \
-            ./qiskit_pkg \
             -e .
             # Build and install both qiskit and qiskit-terra so that any optionals
             # depending on `qiskit` will resolve correctly.

.azure/test-windows.yml

@@ -42,7 +42,6 @@ jobs:
             -c constraints.txt \
             -r requirements.txt \
             -r requirements-dev.txt \
-            ./qiskit_pkg \
             -e .
           # Build and install both qiskit and qiskit-terra so that any optionals
           # depending on `qiskit` will resolve correctly.

.github/workflows/coverage.yml

@@ -42,7 +42,7 @@ jobs:
         run: python -m pip install -c constraints.txt --upgrade pip setuptools wheel
 
       - name: Build and install qiskit-terra
-        run: python -m pip install -c constraints.txt -e . ./qiskit_pkg
+        run: python -m pip install -c constraints.txt -e .
         env:
           CARGO_INCREMENTAL: 0
           RUSTFLAGS: "-Cinstrument-coverage"

.github/workflows/slow.yml

@@ -19,7 +19,7 @@ jobs:
           python -m pip install -U pip setuptools wheel
           python -m pip install -U -r requirements.txt -c constraints.txt
           python -m pip install -U -r requirements-dev.txt -c constraints.txt
-          python -m pip install -c constraints.txt -e . ./qiskit_pkg
+          python -m pip install -c constraints.txt -e .
           python -m pip install "qiskit-aer" "z3-solver" "cplex" -c constraints.txt
         env:
           SETUPTOOLS_ENABLE_FEATURES: "legacy-editable"

.github/workflows/wheels.yml

@@ -168,7 +168,7 @@ jobs:
         with:
           packages-dir: wheelhouse/
   sdist:
-    name: Build and publish terra sdist
+    name: Build and publish sdist
     runs-on: ${{ matrix.os }}
     needs: ["upload_shared_wheels"]
     environment: release
@@ -190,31 +190,3 @@ jobs:
         run: python -m build . --sdist
       - name: Publish package distributions to PyPI
         uses: pypa/gh-action-pypi-publish@release/v1
-  metapackage:
-    name: Build and publish terra sdist
-    runs-on: ${{ matrix.os }}
-    needs: ["sdist"]
-    environment: release
-    permissions:
-      id-token: write
-    strategy:
-      fail-fast: false
-      matrix:
-        os: [ubuntu-latest]
-    steps:
-      - uses: actions/checkout@v3
-      - uses: actions/setup-python@v4
-        name: Install Python
-        with:
-          python-version: '3.10'
-      - name: Install deps
-        run: pip install -U twine setuptools-rust wheel build
-      - name: Build packages
-        run: |
-          set -e
-          cd qiskit_pkg
-          python -m build .
-      - name: Publish package distributions to PyPI
-        uses: pypa/gh-action-pypi-publish@release/v1
-        with:
-          packages-dir: qiskit_pkg/dist

releasenotes/notes/terra-nullius-7ef598626d8118c1.yaml

@@ -0,0 +1,29 @@
+---
+critical:
+  - |
+    You cannot upgrade in place to Qiskit 1.0.  You must begin a new virtual environment.
+
+    From Qiskit 1.0, Qiskit is comprised of exactly one Python package: ``qiskit``.  Previously,
+    as a legacy of the "component elements" of early Qiskit, the ``qiskit`` package was a
+    dependency-only "metapackage", and the core code of Qiskit was in a package called ``qiskit-terra``.
+    As Qiskit grew, the other elements split off into their own packages (such as ``qiskit-aer``)
+    until only the core was left in the metapackage.  For Qiskit 1.0, we are removing the metapackage
+    entirely, and replacing it with the actual Qiskit code.
+
+    This means that you cannot upgrade an existing installation to Qiskit 1.0.  Instead, you must
+    create a new Python virtual environment.  Using the built-in ``venv`` module, you can do (Linux
+    and Mac):
+
+    .. code-block:: bash
+
+      # Create the new environment (only once).
+      python -m venv ~/qiskit-1.0-venv
+      # Activate the environment (every session).
+      source ~/qiskit-1.0-venv/bin/activate
+      # Install Qiskit (only once).
+      pip install 'qiskit>=1.0'
+
+    On Windows, replace ``source <venv>/bin/activate`` with ``source <venv>/Scripts/activate``.
+
+    If you are a library author, or have code that depends on Qiskit, you should update any old
+    dependencies on ``qiskit-terra`` to instead depend on ``qiskit``.

setup.py

@@ -56,7 +56,7 @@
 
 
 setup(
-    name="qiskit-terra",
+    name="qiskit",
     version="1.0.0",
     description="Software for developing quantum computing programs",
     long_description=README,

tools/deploy_translatable_strings.sh

@@ -84,8 +84,9 @@ rm -rf \
 echo "+ 'cp' wanted files from source to target"
 # Copy the new rendered files and add them to the commit.
 cp -r "$SOURCE_PO_DIR/." "$TARGET_PO_DIR"
-# Copy files necessary to build the Qiskit metapackage.
-cp "$SOURCE_REPO_ROOT/qiskit_pkg/setup.py" "${TARGET_REPO_ROOT}"
+# Copy files necessary to build the Qiskit package.
+cp "$SOURCE_REPO_ROOT/setup.py" "${TARGET_REPO_ROOT}"
+cp "$SOURCE_REPO_ROOT/pyproject.toml" "${TARGET_REPO_ROOT}"
 cat "$SOURCE_REPO_ROOT/requirements-dev.txt" "$SOURCE_REPO_ROOT/requirements-optional.txt" \
     > "${TARGET_REPO_ROOT}/requirements-dev.txt"
 cp "$SOURCE_REPO_ROOT/constraints.txt" "${TARGET_REPO_ROOT}"

tox.ini

@@ -4,10 +4,6 @@ envlist = py38, py39, py310, py311, py312, lint-incr
 isolated_build = true
 
 [testenv]
-# We pretend that we're not actually installing the package, because we need tox to let us have two
-# packages ('qiskit' and 'qiskit-terra') under test at the same time.  For that, we have to stuff
-# them into 'deps'.
-skip_install = true
 install_command = pip install -c{toxinidir}/constraints.txt -U {opts} {packages}
 setenv =
   VIRTUAL_ENV={envdir}
@@ -22,16 +18,14 @@ deps =
     setuptools_rust  # This is work around for the bug of tox 3 (see #8606 for more details.)
     -r{toxinidir}/requirements.txt
     -r{toxinidir}/requirements-dev.txt
-    -e .
-    -e ./qiskit_pkg
 commands =
   stestr run {posargs}
 
 [testenv:lint]
 basepython = python3
 commands =
-  ruff check qiskit test tools examples setup.py qiskit_pkg
-  black --check {posargs} qiskit test tools examples setup.py qiskit_pkg
+  ruff check qiskit test tools examples setup.py
+  black --check {posargs} qiskit test tools examples setup.py
   pylint -rn qiskit test tools
   # This line is commented out until #6649 merges. We can't run this currently
   # via tox because tox doesn't support globbing
@@ -45,8 +39,8 @@ commands =
 basepython = python3
 allowlist_externals = git
 commands =
-  ruff check qiskit test tools examples setup.py qiskit_pkg
-  black --check {posargs} qiskit test tools examples setup.py qiskit_pkg
+  ruff check qiskit test tools examples setup.py
+  black --check {posargs} qiskit test tools examples setup.py
   -git fetch -q https://github.com/Qiskit/qiskit-terra.git :lint_incr_latest
   python {toxinidir}/tools/pylint_incr.py -rn -j4 -sn --paths :/qiskit/*.py :/test/*.py :/tools/*.py
   python {toxinidir}/tools/pylint_incr.py -rn -j4 -sn --disable='invalid-name,missing-module-docstring,redefined-outer-name' --paths :(glob,top)examples/python/*.py
@@ -59,7 +53,7 @@ commands =
 skip_install = true
 deps =
     -r requirements-dev.txt
-commands = black {posargs} qiskit test tools examples setup.py qiskit_pkg
+commands = black {posargs} qiskit test tools examples setup.py
 
 [testenv:coverage]
 basepython = python3