feat(#1100): add broad-scope lint

src/main/resources/org/eolang/lints/design/broad-scope.xsl

@@ -0,0 +1,42 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+* SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+* SPDX-License-Identifier: MIT
+-->
+<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:eo="https://www.eolang.org" version="2.0" id="broad-scope">
+  <xsl:import href="/org/eolang/funcs/lineno.xsl"/>
+  <xsl:import href="/org/eolang/funcs/escape.xsl"/>
+  <xsl:import href="/org/eolang/funcs/defect-context.xsl"/>
+  <xsl:output encoding="UTF-8" method="xml"/>
+  <xsl:key name="referenced-by-name" match="o[@base]" use="if (matches(@base, '^ξ(?:\.ρ)*\.')) then tokenize(replace(@base, '^ξ(?:\.ρ)*\.', ''), '\.')[1] else ''"/>
+  <xsl:template match="/">
+    <defects>
+      <xsl:for-each select="//o[@local and @name and not(@name='φ')]">
+        <xsl:variable name="parent" select="parent::o"/>
+        <xsl:variable name="refs" select="key('referenced-by-name', @name)"/>
+        <xsl:variable name="containers" select="$refs/ancestor::o[parent::o[generate-id() = generate-id($parent)]][1]"/>
+        <xsl:if test="count($refs) &gt; 0 and count($containers) = count($refs) and count(distinct-values($containers/generate-id())) = 1 and not(exists($containers[generate-id() = generate-id(current())]))">
+          <xsl:element name="defect">
+            <xsl:variable name="line" select="eo:lineno(@line)"/>
+            <xsl:attribute name="line">
+              <xsl:value-of select="$line"/>
+            </xsl:attribute>
+            <xsl:if test="$line = '0'">
+              <xsl:attribute name="context">
+                <xsl:value-of select="eo:defect-context(.)"/>
+              </xsl:attribute>
+            </xsl:if>
+            <xsl:attribute name="severity">
+              <xsl:text>warning</xsl:text>
+            </xsl:attribute>
+            <xsl:text>The private attribute </xsl:text>
+            <xsl:value-of select="eo:escape(@local)"/>
+            <xsl:text> is used only inside the object </xsl:text>
+            <xsl:value-of select="eo:escape(($containers[1]/@local, $containers[1]/@name)[1])"/>
+            <xsl:text>, its scope is too broad</xsl:text>
+          </xsl:element>
+        </xsl:if>
+      </xsl:for-each>
+    </defects>
+  </xsl:template>
+</xsl:stylesheet>

src/main/resources/org/eolang/motives/design/broad-scope.md

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+# Broad scope
+
+A private attribute should be declared as close as possible to its only
+usage. If a private attribute is used only inside a single nested object,
+declaring it on the level of the parent object makes its scope unnecessarily
+broad.
+
+Incorrect:
+
+```eo
+[] > foo
+  42 >> a
+  [] >> b
+    a.plus 1 > c
+```
+
+Here, the scope of `a` is too broad: it is used only inside `b`. It should be
+moved closer, into `b`:
+
+```eo
+[] > foo
+  [] >> b
+    42 >> a
+    a.plus 1 > c
+```

src/test/resources/org/eolang/lints/packs/single/broad-scope/allows-used-in-multiple-objects.yaml

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+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/design/broad-scope.xsl
+asserts:
+  - /defects[count(defect[@severity='warning'])=0]
+input: |
+  [] > foo
+    42 >> a
+    [] >> b
+      a.plus 1 > c
+    [] > z
+      a.plus 2 > d

src/test/resources/org/eolang/lints/packs/single/broad-scope/allows-used-on-top-level.yaml

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+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/design/broad-scope.xsl
+asserts:
+  - /defects[count(defect[@severity='warning'])=0]
+input: |
+  [] > foo
+    42 >> a
+    a.plus 1 > c
+    [] >> b
+      a.plus 2 > d

src/test/resources/org/eolang/lints/packs/single/broad-scope/catches-broad-scope.yaml

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+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/lints/design/broad-scope.xsl
+asserts:
+  - /defects[count(defect[@severity='warning'])=1]
+  - /defects/defect[@line='2']
+input: |
+  [] > foo
+    42 >> a
+    [] >> b
+      a.plus 1 > c