fix(code-placeholders): reject shell arithmetic placeholders

apps/sim/lib/execution/code-placeholders/compiler.test.ts

@@ -1039,6 +1039,64 @@ describe('code placeholder compiler', () => {
     }
   })
 
+  it.each([
+    'total=$(( {{KEY}} * 2 ))',
+    'printf "%s" "$(( {{KEY}} * 2 ))"',
+    'total=$(( "{{KEY}}" * 2 ))',
+    'total=$[ {{KEY}} * 2 ]',
+    'printf "%s" "$[ {{KEY}} * 2 ]"',
+    'total=$[ values[0] + {{KEY}} ]',
+    '(( total = {{KEY}} * 2 ))',
+    'for (( i = {{KEY}}; i < 2; i++ )); do :; done',
+    'total=$(( $(printf "%s" "{{KEY}}") * 2 ))',
+    'total=$(( `printf "%s" "{{KEY}}"` * 2 ))',
+    'total=$(( $(( 1 + 1 )) + {{KEY}} ))',
+    'cat <<PAYLOAD\n$(( {{KEY}} * 2 ))\nPAYLOAD',
+    'cat <<PAYLOAD\n$[ {{KEY}} * 2 ]\nPAYLOAD',
+  ])('rejects shell placeholders whose values enter arithmetic: %s', async (code) => {
+    await expect(
+      compileCodePlaceholders({
+        code,
+        language: CodeLanguage.Shell,
+        environmentVariables: { KEY: 'values[$(printf injected >&2)]' },
+      })
+    ).rejects.toThrow('is not supported in shell arithmetic')
+  })
+
+  it('preserves shell literal arithmetic text and leaves completed arithmetic frames', async () => {
+    const value = 'values[$(printf injected >&2)]'
+    const compiled = await compileCodePlaceholders({
+      code: [
+        'printf "%s\\n" "{{KEY}}"',
+        "printf '%s\\n' '$(( {{KEY}} ))'",
+        "printf '%s\\n' '$[ {{KEY}} ]'",
+        'printf "%s\\n" "$(printf %s "{{KEY}}")"',
+        'printf "%s\\n" "$(( 1 + 1 )){{KEY}}"',
+        'printf "%s\\n" "$[ values[0] + 2 ]{{KEY}}"',
+        '(( total = 2 )); printf "%s\\n" "{{KEY}}"',
+        'cat <<PAYLOAD',
+        '(( {{KEY}} ))',
+        'PAYLOAD',
+      ].join('\n'),
+      language: CodeLanguage.Shell,
+      environmentVariables: { KEY: value },
+    })
+
+    expect(executeShell(compiled.code, compiled.bindings)).toBe(
+      `${value}\n$(( ${value} ))\n$[ ${value} ]\n${value}\n2${value}\n2${value}\n${value}\n(( ${value} ))\n`
+    )
+  })
+
+  it('discovers shell arithmetic placeholders without compiling missing values', async () => {
+    const code = 'total=$(( {{MISSING}} + {{KEY}} ))'
+    await expect(analyzeCodePlaceholders(code, CodeLanguage.Shell)).resolves.toEqual([
+      'MISSING',
+      'KEY',
+    ])
+    const compiled = await compileCodePlaceholders({ code, language: CodeLanguage.Shell })
+    expect(compiled.code).toBe(code)
+  })
+
   it('renders quoted shell heredocs nested in double-quoted command substitutions', async () => {
     const compiled = await compileCodePlaceholders({
       code: [

apps/sim/lib/execution/code-placeholders/shell.ts

@@ -31,11 +31,14 @@ interface ShellScanFrame {
   kind: 'root' | 'command' | 'arithmetic' | 'backtick'
   quote: ShellQuote
   parenthesisDepth: number
+  bracketDepth?: number
   literalRoot: boolean
 }
 
 interface ShellOccurrenceContext {
   quote: ShellQuote
+  /** Includes nested command substitutions whose output can become an arithmetic operand. */
+  arithmetic?: boolean
   unsupported?: 'escaped sequence'
 }
 
@@ -445,10 +448,11 @@ function isShellAssignmentName(code: string, occurrence: CodePlaceholderOccurren
 function getUnsupportedShellPosition(
   code: string,
   occurrence: CodePlaceholderOccurrence,
-  quote: ShellQuote
+  context: ShellOccurrenceContext
 ): string | undefined {
+  if (context.arithmetic) return 'in shell arithmetic'
   if (code[occurrence.start - 1] === '$') return 'immediately after "$"'
-  if (quote !== 'none') return undefined
+  if (context.quote !== 'none') return undefined
 
   const lineStart = Math.max(
     code.lastIndexOf('\n', occurrence.start - 1),
@@ -488,6 +492,7 @@ function collectShellOccurrenceContexts(
     { kind: 'root', quote: 'none', parenthesisDepth: 0, literalRoot },
   ]
   let skippedRangeIndex = 0
+  let arithmeticDepth = 0
 
   for (let index = start; index < end; ) {
     const frame = frames.at(-1)
@@ -507,7 +512,7 @@ function collectShellOccurrenceContexts(
 
     const occurrence = occurrenceByStart.get(index)
     if (occurrence) {
-      contexts.set(occurrence, { quote: frame.quote })
+      contexts.set(occurrence, { quote: frame.quote, arithmetic: arithmeticDepth > 0 })
       index = occurrence.end
       continue
     }
@@ -533,6 +538,24 @@ function collectShellOccurrenceContexts(
       }
       continue
     }
+    const arithmeticExpansion =
+      character === '$' &&
+      ((code[index + 1] === '(' && code[index + 2] === '(') || code[index + 1] === '[')
+    const arithmeticCommand =
+      frame.quote === 'none' && !frame.literalRoot && shellArithmeticCommandStarts(code, index)
+    if (arithmeticExpansion || arithmeticCommand) {
+      const brackets = arithmeticExpansion && code[index + 1] === '['
+      frames.push({
+        kind: 'arithmetic',
+        quote: 'none',
+        parenthesisDepth: brackets ? 0 : 2,
+        ...(brackets ? { bracketDepth: 1 } : {}),
+        literalRoot: false,
+      })
+      arithmeticDepth += 1
+      index += arithmeticExpansion && !brackets ? 3 : 2
+      continue
+    }
     if (frame.quote === 'double') {
       if (character === '\\') {
         const escaped = occurrenceByStart.get(index + 1)
@@ -572,7 +595,7 @@ function collectShellOccurrenceContexts(
       index += 1
       continue
     }
-    if (!frame.literalRoot && shellCommentStarts(code, index)) {
+    if (frame.kind !== 'arithmetic' && !frame.literalRoot && shellCommentStarts(code, index)) {
       const newline = code.indexOf('\n', index)
       index = newline === -1 || newline >= end ? end : newline + 1
       continue
@@ -622,14 +645,29 @@ function collectShellOccurrenceContexts(
       index += 1
       continue
     }
-    if (frame.kind === 'command' && character === '(') {
+    if (frame.kind === 'arithmetic' && frame.bracketDepth !== undefined) {
+      if (character === '[') frame.bracketDepth += 1
+      if (character === ']') {
+        frame.bracketDepth -= 1
+        if (frame.bracketDepth === 0) {
+          frames.pop()
+          arithmeticDepth -= 1
+        }
+      }
+      index += 1
+      continue
+    }
+    if ((frame.kind === 'command' || frame.kind === 'arithmetic') && character === '(') {
       frame.parenthesisDepth += 1
       index += 1
       continue
     }
-    if (frame.kind === 'command' && character === ')') {
+    if ((frame.kind === 'command' || frame.kind === 'arithmetic') && character === ')') {
       frame.parenthesisDepth -= 1
-      if (frame.parenthesisDepth === 0) frames.pop()
+      if (frame.parenthesisDepth === 0) {
+        frames.pop()
+        if (frame.kind === 'arithmetic') arithmeticDepth -= 1
+      }
       index += 1
       continue
     }
@@ -849,7 +887,7 @@ export async function compileShellPlaceholders(
       const unsupportedPosition = getUnsupportedShellPosition(
         input.code,
         occurrence,
-        occurrenceContext.quote
+        occurrenceContext
       )
       if (unsupportedPosition) {
         if (context.hasValue(occurrence.name)) {
@@ -904,7 +942,7 @@ export async function compileShellPlaceholders(
     const unsupportedPosition = getUnsupportedShellPosition(
       input.code,
       occurrence,
-      occurrenceContext.quote
+      occurrenceContext
     )
     if (unsupportedPosition) {
       if (context.hasValue(occurrence.name)) {