[BUG] `build.sh`: `--cmake-args` are mangled for the `cuopt` Python package

[mlubin]

Summary

When build.sh builds the cuopt Python package, it forwards --cmake-args to
scikit-build via SKBUILD_CMAKE_ARGS. The expression that assembles that string
uses ${EXTRA_CMAKE_ARGS[*]// /;}, which does not join the array elements
with ;. As a result, whenever the user passes --cmake-args, the user's flag
and the auto-appended -DFIND_CUOPT_CPP=ON are concatenated into a single
cmake argument separated by a space, corrupting both.

Version

• NVIDIA/cuopt main (VERSION 26.08.00), build.sh line 420, in the
  cuopt Python package build block.

Affected code

build.sh line 420, in the if buildAll || hasArg cuopt; then block:

cuopt/build.sh

Lines 419 to 421 in 37a7b63

	# $EXTRA_CMAKE_ARGS gets concatenated into a string with [*] and then we find/replace spaces with semi-colons
	SKBUILD_CMAKE_ARGS="-DCMAKE_PREFIX_PATH=${INSTALL_PREFIX};-DCMAKE_LIBRARY_PATH=${LIBCUOPT_BUILD_DIR};-DCMAKE_CUDA_ARCHITECTURES=${CUOPT_CMAKE_CUDA_ARCHITECTURES};${EXTRA_CMAKE_ARGS[*]// /;}" \
	python "${PYTHON_ARGS_FOR_INSTALL[@]}" .

Relevant surrounding code:

# EXTRA_CMAKE_ARGS is populated by word-splitting the --cmake-args value:
read -ra EXTRA_CMAKE_ARGS <<< "$EXTRA_CMAKE_ARGS"

# ...and build.sh always appends this unless the user already set it:
if ! contains_string "DFIND_CUOPT_CPP" "${EXTRA_CMAKE_ARGS[@]}"; then
    EXTRA_CMAKE_ARGS+=("-DFIND_CUOPT_CPP=ON")
fi

Root cause

${arr[*]//pattern/repl} in bash applies the substitution to each element
individually, and only then joins the elements using the first character of
IFS. IFS is unset/default here, so the first character is a space.

Because EXTRA_CMAKE_ARGS is built with read -ra (word-split on whitespace),
its elements are individual, space-free tokens. The space -> ; substitution
therefore matches nothing inside any element, and the spaces that join the
elements are left untouched. The intended transformation ("replace the joining
spaces with semicolons") never happens — the code assumes the join occurs before
the substitution, but the order is the reverse.

Reproduction

# Minimal, using the exact upstream expression and the array build.sh produces:
EXTRA_CMAKE_ARGS=()
read -ra EXTRA_CMAKE_ARGS <<< "-DCMAKE_CUDA_ARCHITECTURES=90-real"   # user --cmake-args
EXTRA_CMAKE_ARGS+=("-DFIND_CUOPT_CPP=ON")                            # auto-appended

printf '%s\n' "${EXTRA_CMAKE_ARGS[*]// /;}"
# Actual:   -DCMAKE_CUDA_ARCHITECTURES=90-real -DFIND_CUOPT_CPP=ON     <-- space
# Expected: -DCMAKE_CUDA_ARCHITECTURES=90-real;-DFIND_CUOPT_CPP=ON     <-- semicolon

End to end:

./build.sh cuopt --cmake-args="-DCMAKE_CUDA_ARCHITECTURES=90-real"

SKBUILD_CMAKE_ARGS ends as:

...;-DCMAKE_CUDA_ARCHITECTURES=<default>;-DCMAKE_CUDA_ARCHITECTURES=90-real -DFIND_CUOPT_CPP=ON

scikit-build splits SKBUILD_CMAKE_ARGS on ;, so the final element becomes a
single cmake argument:

-DCMAKE_CUDA_ARCHITECTURES=90-real -DFIND_CUOPT_CPP=ON

i.e. cmake sees CMAKE_CUDA_ARCHITECTURES set to the literal string
90-real -DFIND_CUOPT_CPP=ON, and FIND_CUOPT_CPP is never set.

Expected vs. actual

• Expected: each --cmake-args flag (and the auto-appended
  -DFIND_CUOPT_CPP=ON) is passed to cmake as a separate -D… argument.
• Actual: when --cmake-args is supplied, the user flag and
  -DFIND_CUOPT_CPP=ON collapse into one malformed argument; the CUDA
  architecture value is corrupted and FIND_CUOPT_CPP is dropped.

Impact

• Latent, but a hard failure on the affected path. It only triggers when
  EXTRA_CMAKE_ARGS has ≥2 elements, which happens whenever the user passes
  any --cmake-args (their token + the always-appended -DFIND_CUOPT_CPP=ON).
• With no --cmake-args, the array has a single element, there is nothing to
  join, and the expression is a harmless no-op — which is why default and CI
  builds don't hit it.
• Notably breaks the common need to pin -DCMAKE_CUDA_ARCHITECTURES explicitly
  (e.g. building in a container where the default NATIVE cannot query a GPU).

Suggested fix

Join the array elements with ; explicitly instead of relying on the (incorrect)
per-element substitution. Set IFS for just the [*] expansion:

SKBUILD_CMAKE_ARGS="-DCMAKE_PREFIX_PATH=${INSTALL_PREFIX};-DCMAKE_LIBRARY_PATH=${LIBCUOPT_BUILD_DIR};-DCMAKE_CUDA_ARCHITECTURES=${CUOPT_CMAKE_CUDA_ARCHITECTURES};$(IFS=';'; echo "${EXTRA_CMAKE_ARGS[*]}")" \
    python "${PYTHON_ARGS_FOR_INSTALL[@]}" .

With this change the reproduction above yields the expected
...;-DCMAKE_CUDA_ARCHITECTURES=90-real;-DFIND_CUOPT_CPP=ON, and each flag reaches
cmake as its own argument.

The buggy pattern appears once (the cuopt block); no other SKBUILD_CMAKE_ARGS
assignment in build.sh uses it.