Add support for .tools-versions (#531)

Closes: #504

src/version/resolve.ts

@@ -2,6 +2,7 @@ import fs from "node:fs";
 import * as core from "@actions/core";
 import { getRequiredVersionFromConfigFile } from "./config-file";
 import { getUvVersionFromRequirementsFile } from "./requirements-file";
+import { getUvVersionFromToolVersions } from "./tool-versions-file";
 
 export function getUvVersionFromFile(filePath: string): string | undefined {
   core.info(`Trying to find version for uv in: ${filePath}`);
@@ -11,7 +12,10 @@ export function getUvVersionFromFile(filePath: string): string | undefined {
   }
   let uvVersion: string | undefined;
   try {
-    uvVersion = getRequiredVersionFromConfigFile(filePath);
+    uvVersion = getUvVersionFromToolVersions(filePath);
+    if (uvVersion === undefined) {
+      uvVersion = getRequiredVersionFromConfigFile(filePath);
+    }
     if (uvVersion === undefined) {
       uvVersion = getUvVersionFromRequirementsFile(filePath);
     }

src/version/tool-versions-file.ts

@@ -0,0 +1,31 @@
+import fs from "node:fs";
+import * as core from "@actions/core";
+
+export function getUvVersionFromToolVersions(
+  filePath: string,
+): string | undefined {
+  if (!filePath.endsWith(".tool-versions")) {
+    return undefined;
+  }
+  const fileContents = fs.readFileSync(filePath, "utf8");
+  const lines = fileContents.split("\n");
+
+  for (const line of lines) {
+    // Skip commented lines
+    if (line.trim().startsWith("#")) {
+      continue;
+    }
+    const match = line.match(/^\s*uv\s*v?\s*(?<version>[^\s]+)\s*$/);
+    if (match) {
+      const matchedVersion = match.groups?.version.trim();
+      if (matchedVersion?.startsWith("ref")) {
+        core.warning(
+          "The ref syntax of .tool-versions is not supported. Please use a released version instead.",
+        );
+        return undefined;
+      }
+      return matchedVersion;
+    }
+  }
+  return undefined;
+}