[Resistor Duo analyzer (#127)] Add feedback to extract the constant to the top level if defined locally

src/analyzers/practice/resistor-color-duo/ResistorColorDuoSolution.ts

@@ -4,6 +4,7 @@ import {
   ExtractedVariable,
   extractExports,
   extractFunctions,
+  extractVariables,
   findAll,
   findFirst,
   findTopLevelConstants,
@@ -480,6 +481,18 @@ class Entry {
     return parameterName(this.params[0])
   }
 
+  public get nameOfConstantDefinedInBody(): string | null {
+    const localConstants = extractVariables(this.body).filter(
+      (constant) =>
+        constant.init?.type === AST_NODE_TYPES.ArrayExpression ||
+        constant.init?.type === AST_NODE_TYPES.ObjectExpression
+    )
+    if (localConstants.length) {
+      return localConstants[0].name || 'COLORS'
+    }
+    return null
+  }
+
   public isOptimal(
     constant: Readonly<Constant> | undefined,
     program: Program
@@ -508,6 +521,11 @@ class Entry {
       }
     }
 
+    if (!constant && !!this.nameOfConstantDefinedInBody) {
+      logger.log('~> found a constant that was not declared at the top level')
+      return false
+    }
+
     if (this.hasOneMap) {
       logger.log('~> is a map solution')
       return this.isOptimalMapSolution(logger, this.body, constant, program)
@@ -1181,6 +1199,10 @@ export class ResistorColorDuoSolution {
     return this.fileConstants.length === 1
   }
 
+  public get shouldExtractTopLevelConstant(): boolean {
+    return !this.mainConstant && !!this.entry.nameOfConstantDefinedInBody
+  }
+
   public get hasOptimalEntry(): boolean {
     return this.entry.isOptimal(this.mainConstant, this.program)
   }

src/analyzers/practice/resistor-color-duo/index.ts

@@ -120,6 +120,23 @@ const ISSUE_UNEXPECTED_CALL = factory<'unexpected' | 'expected'>`
   CommentType.Actionable
 )
 
+const PREFER_EXTRACTED_TOP_LEVEL_CONSTANT = factory<
+  'value' | 'name' | 'method.signature'
+>`
+📕 Instead of defining the constant _inside_ the function, consider extracting it
+to the top-level. Constants, functions, and classes that are not \`export\`ed,
+are not accessible from outside the file.
+
+\`\`\`javascript
+const ${'name'} = ${'value'}
+
+export ${'method.signature'}
+\`\`\`
+`(
+  'javascript.resistor-color-duo.prefer_extracted_top_level_constant',
+  CommentType.Actionable
+)
+
 type Program = TSESTree.Program
 
 export class ResistorColorDuoAnalyzer extends IsolatedAnalyzerImpl {
@@ -287,6 +304,16 @@ export class ResistorColorDuoAnalyzer extends IsolatedAnalyzerImpl {
     solution: ResistorColorDuoSolution,
     output: WritableOutput
   ): void | never {
+    if (solution.shouldExtractTopLevelConstant) {
+      output.add(
+        PREFER_EXTRACTED_TOP_LEVEL_CONSTANT({
+          name: solution.entry.nameOfConstantDefinedInBody,
+          value: '...',
+          'method.signature': solution.entry.signature,
+        })
+      )
+    }
+
     if (solution || output) {
       return
     }