Pre support (#6)

* First implementation of pre

* Remove an unused thing

* Fix a thing

* Another fix

* Fix some stuff

* Actually fix it

* Update things

index.ts

@@ -11,6 +11,8 @@ import {
   sortTheThings
 } from "./utils";
 import * as semver from "semver";
+import { readPreState } from "@changesets/pre";
+import readChangesets from "@changesets/read";
 
 (async () => {
   let githubToken = process.env.GITHUB_TOKEN;
@@ -20,13 +22,13 @@ import * as semver from "semver";
     return;
   }
   let repo = `${github.context.repo.owner}/${github.context.repo.repo}`;
+  let branch = github.context.ref.replace("refs/heads/", "");
+  let preState = await readPreState(process.cwd());
+
+  let isInPreMode = preState !== undefined && preState.mode === "pre";
 
   const octokit = new github.GitHub(githubToken);
 
-  let defaultBranchPromise = octokit.repos
-    .get(github.context.repo)
-    .then(x => x.data.default_branch);
-
   console.log("setting git user");
   await exec("git", [
     "config",
@@ -47,28 +49,14 @@ import * as semver from "semver";
     `machine github.com\nlogin github-actions[bot]\npassword ${githubToken}`
   );
 
-  let defaultBranch = await defaultBranchPromise;
-  if (github.context.ref.replace("refs/heads/", "") !== defaultBranch) {
-    core.setFailed(
-      `The changesets action should only run on ${defaultBranch} but it's running on ${github.context.ref.replace(
-        "refs/heads/",
-        ""
-      )}, please change your GitHub actions config to only run the Changesets action on ${defaultBranch}`
-    );
-    return;
+  let changesets = await readChangesets(process.cwd());
+
+  if (isInPreMode) {
+    let changesetsToFilter = new Set(preState.changesets);
+    changesets = changesets.filter(x => !changesetsToFilter.has(x.id));
   }
 
-  let hasChangesets = fs
-    .readdirSync(`${process.cwd()}/.changeset`)
-    .some(
-      x =>
-        x !== "README.md" &&
-        x !== "config.js" &&
-        x !== "config.json" &&
-        !x.endsWith(".js")
-    );
-
-  console.log(fs.readdirSync(`${process.cwd()}/.changeset`));
+  let hasChangesets = changesets.length !== 0;
 
   let publishScript = core.getInput("publish");
 
@@ -99,8 +87,9 @@ import * as semver from "semver";
       publishCommand,
       publishArgs
     );
+    await exec("git", ["pull", "origin", branch]);
 
-    await exec("git", ["push", "origin", `HEAD:${defaultBranch}`, "--tags"]);
+    await exec("git", ["push", "origin", `HEAD:${branch}`, "--tags"]);
 
     let newTagRegex = /New tag:\s+(@[^/]+\/[^@]+|[^/]+)@([^\s]+)/;
 
@@ -161,16 +150,15 @@ import * as semver from "semver";
   }
 
   if (hasChangesets) {
-    let { stderr } = await execWithOutput(
-      "git",
-      ["checkout", "changeset-release"],
-      { ignoreReturnCode: true }
-    );
+    let versionBranch = `changeset-release/${branch}`;
+    let { stderr } = await execWithOutput("git", ["checkout", versionBranch], {
+      ignoreReturnCode: true
+    });
     let isCreatingChangesetReleaseBranch = !stderr
       .toString()
-      .includes("Switched to a new branch 'changeset-release'");
+      .includes(`Switched to a new branch '${versionBranch}'`);
     if (isCreatingChangesetReleaseBranch) {
-      await exec("git", ["checkout", "-b", "changeset-release"]);
+      await exec("git", ["checkout", "-b", versionBranch]);
     }
 
     await exec("git", ["reset", "--hard", github.context.sha]);
@@ -184,7 +172,7 @@ import * as semver from "semver";
       "./node_modules/.bin/changeset",
       cmd
     ]);
-    let searchQuery = `repo:${repo}+state:open+head:changeset-release+base:${defaultBranch}`;
+    let searchQuery = `repo:${repo}+state:open+head:${versionBranch}+base:${branch}`;
     let searchResultPromise = octokit.search.issuesAndPullRequests({
       q: searchQuery
     });
@@ -196,8 +184,18 @@ import * as semver from "semver";
           publishScript
             ? `the packages will be published to npm automatically`
             : `publish to npm yourself or [setup this action to publish automatically](https://github.com/changesets/action#with-publishing)`
-        }. If you're not ready to do a release yet, that's fine, whenever you add more changesets to ${defaultBranch}, this PR will be updated.
+        }. If you're not ready to do a release yet, that's fine, whenever you add more changesets to ${branch}, this PR will be updated.
+${
+  isInPreMode
+    ? `
+⚠️⚠️⚠️⚠️⚠️⚠️
 
+\`${branch}\` is currently in **pre mode** so this branch has prereleases rather than normal releases. If you want to exit prereleases, run \`changeset pre exit\` on \`${branch}\`.
+
+⚠️⚠️⚠️⚠️⚠️⚠️
+`
+    : ""
+}
 # Releases
 ` +
         (await Promise.all(
@@ -228,14 +226,14 @@ import * as semver from "semver";
     })();
     await exec("git", ["add", "."]);
     await exec("git", ["commit", "-m", "Version Packages"]);
-    await exec("git", ["push", "origin", "changeset-release", "--force"]);
+    await exec("git", ["push", "origin", versionBranch, "--force"]);
     let searchResult = await searchResultPromise;
     console.log(JSON.stringify(searchResult.data, null, 2));
     if (searchResult.data.items.length === 0) {
       console.log("creating pull request");
       await octokit.pulls.create({
-        base: defaultBranch,
-        head: "changeset-release",
+        base: branch,
+        head: versionBranch,
         title: "Version Packages",
         body: await prBodyPromise,
         ...github.context.repo