Add Cloudflare Pages automatic preview deploy detection (#49823)

Addresses get-convex/convex-backend#440

Adds automatic Cloudflare Pages preview deployment detection to `convex deploy`, matching the existing Vercel/Netlify behavior. When `CF_PAGES` is set, the CLI now uses `CF_PAGES_BRANCH` as the preview deployment name and detects non-production builds via a branch name heuristic.

GitOrigin-RevId: f7a1ff7c4c9770630309c7ee299162141bfffec5

Author: ianmacartney

src/cli/deploy.ts

@@ -49,7 +49,7 @@ export const deploy = new Command("deploy")
   .addOption(
     new Option(
       "--preview-create <name>",
-      "The name to associate with this deployment if deploying to a newly created preview deployment. Defaults to the current Git branch name in Vercel, Netlify and GitHub CI. This parameter can only be used with a preview deploy key (when used with another type of key, the command will return an error).",
+      "The name to associate with this deployment if deploying to a newly created preview deployment. Defaults to the current Git branch name in Vercel, Netlify, Cloudflare Pages and GitHub CI. This parameter can only be used with a preview deploy key (when used with another type of key, the command will return an error).",
     ).conflicts("preview-name"),
   )
   .addOption(

src/cli/lib/envvars.ts

@@ -433,7 +433,9 @@ export function getBuildEnvironment(): string | false {
     ? "Vercel"
     : process.env.NETLIFY
       ? "Netlify"
-      : false;
+      : process.env.CF_PAGES || process.env.WORKERS_CI
+        ? "Cloudflare"
+        : false;
 }
 
 export function gitBranchFromEnvironment(): string | null {
@@ -445,6 +447,11 @@ export function gitBranchFromEnvironment(): string | null {
     // https://docs.netlify.com/configure-builds/environment-variables/
     return process.env.HEAD ?? null;
   }
+  if (process.env.CF_PAGES || process.env.WORKERS_CI) {
+    // https://developers.cloudflare.com/pages/configuration/build-configuration/#environment-variables
+    // https://developers.cloudflare.com/workers/ci-cd/builds/configuration/#environment-variables
+    return process.env.CF_PAGES_BRANCH ?? process.env.WORKERS_CI_BRANCH ?? null;
+  }
 
   if (process.env.CI) {
     // https://docs.github.com/en/actions/learn-github-actions/variables
@@ -466,5 +473,13 @@ export function isNonProdBuildEnvironment(): boolean {
     // https://docs.netlify.com/configure-builds/environment-variables/
     return process.env.CONTEXT !== "production";
   }
+  if (process.env.CF_PAGES || process.env.WORKERS_CI) {
+    // https://developers.cloudflare.com/pages/configuration/build-configuration/#environment-variables
+    // https://developers.cloudflare.com/workers/ci-cd/builds/configuration/#environment-variables
+    // Branch !== "main" is the closest heuristic; Cloudflare Pages
+    // does not expose a dedicated production/preview flag.
+    const branch = process.env.CF_PAGES_BRANCH ?? process.env.WORKERS_CI_BRANCH;
+    return branch !== "main";
+  }
   return false;
 }