feat(linter): add cpplint C++ linter

Author: barrettruth

lua/guard-collection/linter/cpplint.lua

@@ -0,0 +1,30 @@
+local lint = require('guard.lint')
+
+return {
+  cmd = 'cpplint',
+  fname = true,
+  stderr = true,
+  ignore_exit_code = true,
+  parse = function(result, bufnr)
+    local diags = {}
+    for line in result:gmatch('[^\n]+') do
+      local lnum, msg, cat, sev = line:match('^[^:]+:(%d+):%s*(.-)%s+%[([^%]]+)%]%s+%[(%d+)%]$')
+      if lnum then
+        local severity = tonumber(sev) >= 3 and vim.diagnostic.severity.ERROR
+          or vim.diagnostic.severity.WARN
+        table.insert(
+          diags,
+          lint.diag_fmt(
+            bufnr,
+            tonumber(lnum) - 1,
+            0,
+            ('[%s] %s'):format(cat, msg),
+            severity,
+            'cpplint'
+          )
+        )
+      end
+    end
+    return diags
+  end,
+}

lua/guard-collection/linter/init.lua

@@ -1,6 +1,7 @@
 return {
   ['clang-tidy'] = require('guard-collection.linter.clang-tidy'),
   codespell = require('guard-collection.linter.codespell'),
+  cpplint = require('guard-collection.linter.cpplint'),
   detekt = require('guard-collection.linter.detekt'),
   eslint = require('guard-collection.linter.eslint'),
   eslint_d = require('guard-collection.linter.eslint_d'),

test/linter/cpplint_spec.lua

@@ -0,0 +1,37 @@
+describe('cpplint', function()
+  it('can lint', function()
+    local helper = require('test.linter.helper')
+    local ns = helper.namespace
+    local ft = require('guard.filetype')
+    ft('cpp'):lint('cpplint')
+
+    local buf, diagnostics = helper.test_with('cpp', {
+      [[// Copyright 2026 Test]],
+      [[int main(){int x=1;}]],
+    })
+    assert.are.same({
+      {
+        bufnr = buf,
+        col = 0,
+        end_col = 0,
+        end_lnum = 1,
+        lnum = 1,
+        message = '[whitespace/operators] Missing spaces around =',
+        namespace = ns,
+        severity = 1,
+        source = 'cpplint',
+      },
+      {
+        bufnr = buf,
+        col = 0,
+        end_col = 0,
+        end_lnum = 1,
+        lnum = 1,
+        message = '[whitespace/braces] Missing space before {',
+        namespace = ns,
+        severity = 1,
+        source = 'cpplint',
+      },
+    }, diagnostics)
+  end)
+end)