Support missing versions being present and set in a local .python-version (#3134)

Requested in https://github.com/pyenv/pyenv/issues/2680
for deployments with a stock `.pyenv-version` that can use any
of a number of Python versions
and for compatibility with `uv`.

* Support `pyenv local --force`
* Support `pyenv-version-file-write --force`
* Support `pyenv version-name --force`
* Ignore missing versions when searching for executables
* Display "commmand not found" even when there are nonexistent versions

* exec.bats: replace `python` and `rspec` with something that doesn't exist globally, either
in Ubuntu Github CI, `python` exists globally

libexec/pyenv-exec

@@ -21,7 +21,7 @@ if [ "$1" = "--complete" ]; then
   exec pyenv-shims --short
 fi
 
-PYENV_VERSION="$(pyenv-version-name)"
+PYENV_VERSION="$(pyenv-version-name -f)"
 PYENV_COMMAND="$1"
 
 if [ -z "$PYENV_COMMAND" ]; then
@@ -29,9 +29,9 @@ if [ -z "$PYENV_COMMAND" ]; then
   exit 1
 fi
 
-export PYENV_VERSION
 PYENV_COMMAND_PATH="$(pyenv-which "$PYENV_COMMAND")"
 PYENV_BIN_PATH="${PYENV_COMMAND_PATH%/*}"
+export PYENV_VERSION
 
 OLDIFS="$IFS"
 IFS=$'\n' scripts=(`pyenv-hooks exec`)

libexec/pyenv-local

@@ -2,9 +2,11 @@
 #
 # Summary: Set or show the local application-specific Python version(s)
 #
-# Usage: pyenv local <version> <version2> <..>
+# Usage: pyenv local [-f|--force] [<version> [...]]
 #        pyenv local --unset
 #
+#   -f/--force    Do not verify that the versions being set exist
+#
 # Sets the local application-specific Python version(s) by writing the
 # version name to a file named `.python-version'.
 #
@@ -36,12 +38,25 @@ if [ "$1" = "--complete" ]; then
   exec pyenv-versions --bare
 fi
 
+while [[ $# -gt 0 ]]
+do
+    case "$1" in
+        -f|--force)
+            FORCE=1
+            shift
+            ;;
+        *)
+            break
+            ;;
+    esac
+done
+
 versions=("$@")
 
 if [ "$versions" = "--unset" ]; then
   rm -f .python-version
 elif [ -n "$versions" ]; then
-  pyenv-version-file-write .python-version "${versions[@]}"
+  pyenv-version-file-write ${FORCE:+-f }.python-version "${versions[@]}"
 else
   if version_file="$(pyenv-version-file "$PWD")"; then
     IFS=: versions=($(pyenv-version-file-read "$version_file"))

libexec/pyenv-version-file-write

@@ -1,9 +1,25 @@
 #!/usr/bin/env bash
-# Usage: pyenv version-file-write <file> <version>
+# Usage: pyenv version-file-write [-f|--force] <file> <version> [...]
+#
+#   -f/--force    Don't verify that the versions exist
 
 set -e
 [ -n "$PYENV_DEBUG" ] && set -x
 
+while [[ $# -gt 0 ]]
+do
+    case "$1" in
+        -f|--force)
+            FORCE=1
+            shift
+            ;;
+        *)
+            break
+            ;;
+    esac
+done
+
+
 PYENV_VERSION_FILE="$1"
 shift || true
 versions=("$@")
@@ -14,7 +30,7 @@ if [ -z "$versions" ] || [ -z "$PYENV_VERSION_FILE" ]; then
 fi
 
 # Make sure the specified version is installed.
-pyenv-prefix "${versions[@]}" >/dev/null
+[[ -z $FORCE ]] && pyenv-prefix "${versions[@]}" >/dev/null
 
 # Write the version out to disk.
 # Create an empty file. Using "rm" might cause a permission error.

libexec/pyenv-version-name

@@ -1,8 +1,25 @@
 #!/usr/bin/env bash
 # Summary: Show the current Python version
+#
+#   -f/--force    (Internal) If a version doesn't exist, print it as is rather than produce an error
+
 set -e
 [ -n "$PYENV_DEBUG" ] && set -x
 
+while [[ $# -gt 0 ]]
+do
+    case "$1" in
+        -f|--force)
+            FORCE=1
+            shift
+            ;;
+        *)
+            break
+            ;;
+    esac
+done
+
+
 if [ -z "$PYENV_VERSION" ]; then
   PYENV_VERSION_FILE="$(pyenv-version-file)"
   PYENV_VERSION="$(pyenv-version-file-read "$PYENV_VERSION_FILE" || true)"
@@ -33,16 +50,20 @@ OLDIFS="$IFS"
     # Remove the explicit 'python-' prefix from versions like 'python-3.12'.
     normalised_version="${version#python-}"
     if version_exists "${version}" || [ "$version" = "system" ]; then
-      versions=("${versions[@]}" "${version}")
+      versions+=("${version}")
     elif version_exists "${normalised_version}"; then
-      versions=("${versions[@]}" "${normalised_version}")
+      versions+=("${normalised_version}")
     elif resolved_version="$(pyenv-latest -b "${version}")"; then
-      versions=("${versions[@]}" "${resolved_version}")
+      versions+=("${resolved_version}")
     elif resolved_version="$(pyenv-latest -b "${normalised_version}")"; then
-      versions=("${versions[@]}" "${resolved_version}")
+      versions+=("${resolved_version}")
     else
-      echo "pyenv: version \`$version' is not installed (set by $(pyenv-version-origin))" >&2
-      any_not_installed=1
+      if [[ -n $FORCE ]]; then
+        versions+=("${normalised_version}")
+      else
+        echo "pyenv: version \`$version' is not installed (set by $(pyenv-version-origin))" >&2
+        any_not_installed=1
+      fi
     fi
   done
 }

libexec/pyenv-which

@@ -96,7 +96,6 @@ else
     for version in "${nonexistent_versions[@]}"; do
       echo "pyenv: version \`$version' is not installed (set by $(pyenv-version-origin))" >&2
     done
-    exit 1
   fi
 
   echo "pyenv: $PYENV_COMMAND: command not found" >&2