linux_new: Template de-duplication — Debian (DEB) shared templates

[steelhead31]

Part of: #1445

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Background

The linux_new pipeline maintains separate Debian template files for every supported Java
version under:

jdk/debian/src/main/packaging/temurin/{version}/debian/
jre/debian/src/main/packaging/temurin/{version}/debian/

With 8 active versions (8, 11, 17, 21, 23, 24, 25, 26) × 2 package types (jdk/jre) × ~8 files
per directory, this is ~128 files where the meaningful differences between versions are:

File	What actually differs between versions
control.template.j2	Provides: list grows by ~3 entries per new version (backward-compat declarations)
rules.template.j2	Priority number (e.g. 1111 → 2111); tool list changes at known version thresholds
jinfo.in	Same tool list changes as rules.template.j2
changelog.template.j2	Only the package name token (e.g. temurin-11-jdk) — structure is identical
postinst.in / prerm.in	Only the package name token — logic is identical

Known tool change boundaries:

• JDK < 17: includes jaotc, jjs, pack200, rmic, unpack200
• JDK ≥ 16: adds jpackage
• JDK ≥ 17: removes the above deprecated tools
• JDK ≥ 18: adds jwebserver

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Goal

Replace the per-version template copies with a single shared template set that uses Jinja2
{% for %} / {% if version|int >= N %} logic driven by the version number already passed
to generate_spec.py. Adding a new Java version will require no new template files.

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Prerequisite

⚠️ The golden file baseline (child issue #4 — regression tests) must be committed
before any templates in this issue are changed. The golden files capture current
output to verify the shared templates produce byte-for-byte identical results.

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Scope

New shared templates to create

jdk/debian/src/main/packaging/temurin/shared/debian/
control.template.j2 ← dynamic Provides: list via {% for i in range(2, version|int+1) %}
changelog.template.j2 ← identical across versions; package name via template variable
rules.template.j2 ← priority and tool list via version-threshold conditionals
postinst.in ← identical across versions
prerm.in ← identical across versions
jinfo.in ← tool list via version-threshold conditionals

jre/debian/src/main/packaging/temurin/shared/debian/
(same set — shorter Provides: list, no java-compiler/java-sdk entries)

Jenkinsfile change

The Generate Spec File stage constructs templatebase for Debian at line ~636. Update this
to check for a per-version file first; fall back to shared/debian/ if absent:

// Current
templatebase = "./linux_new/${PTYPE}/${DistArrayElement}/src/main/packaging/${PRODUCT}/${Release}/${DistArrayElement}/${debianFilesArrayElement}.template.j2"

// New (pseudocode)
def versionSpecific = "./linux_new/${PTYPE}/${DistArrayElement}/src/main/packaging/${PRODUCT}/${Release}/${DistArrayElement}/${debianFilesArrayElement}.template.j2"
def shared          = "./linux_new/${PTYPE}/${DistArrayElement}/src/main/packaging/${PRODUCT}/shared/${DistArrayElement}/${debianFilesArrayElement}.template.j2"
templatebase = fileExists(versionSpecific) ? versionSpecific : shared

The same fallback applies for postinst.in, prerm.in, and jinfo.in (non-templated files
copied by build.sh). Update build.sh to source from shared/ when no per-version copy exists.

Per-version directories
Once the shared templates are validated, the per-version debian/ subdirectories can be
deleted, retaining only:

compat (identical across versions — keep in place; no fallback needed, or move to shared)
copyright (identical across versions — same)
Acceptance Criteria
 jdk/debian/src/main/packaging/temurin/shared/debian/ exists with all 6 template/in files
 jre/debian/src/main/packaging/temurin/shared/debian/ exists with all 6 template/in files
 Per-version changelog.template.j2, control.template.j2, rules.template.j2, postinst.in, prerm.in, jinfo.in files are deleted from all 8 version directories
 Running generate_spec.py against the shared templates for all 8 versions produces output that is byte-for-byte identical to the committed golden files (regression test passes)
 Jenkinsfile Generate Spec File stage uses the shared fallback path
 build.sh copies postinst.in, prerm.in, jinfo.in from shared/ when no per-version override exists
 Both jdk and jre are covered