fix: estimator rust version (#7485)

Update docker tag to force re-building any existing older docker images.

runtime/runtime-params-estimator/emu-cost/Dockerfile

@@ -1,5 +1,4 @@
 # our local base image
-# FROM ubuntu
 FROM rust:1.63.0
 
 LABEL description="Container for builds"

runtime/runtime-params-estimator/src/main.rs

@@ -274,10 +274,7 @@ fn main_docker(
     exec("docker --version").context("please install `docker`")?;
 
     let project_root = project_root();
-
-    let image = "rust-emu";
-    let tag = "rust-1.62.1"; //< Update this when Dockerfile changes
-    let tagged_image = format!("{}:{}", image, tag);
+    let tagged_image = docker_image()?;
     if exec(&format!("docker images -q {}", tagged_image))?.is_empty() {
         // Build a docker image if there isn't one already.
         let status = Command::new("docker")
@@ -379,6 +376,26 @@ fn main_docker(
     Ok(())
 }
 
+/// Creates a docker image tag that is unique for each rust version to force re-build when it changes.
+fn docker_image() -> Result<String, anyhow::Error> {
+    let image = "rust-emu";
+    let dockerfile =
+        fs::read_to_string(Path::new(env!("CARGO_MANIFEST_DIR")).join("emu-cost/Dockerfile"))?;
+    // The Dockerfile is expected to have a line like this:
+    // ```
+    // FROM rust:x.y.z
+    // ```
+    // and the result should be `rust-x.y.z`
+    let tag = dockerfile
+        .lines()
+        .find_map(|line| line.split_once("FROM "))
+        .context("could not parse rustc version from Dockerfile")?
+        .1
+        .replace(":", "-");
+
+    Ok(format!("{}:{}", image, tag))
+}
+
 fn read_costs_table(path: &Path) -> anyhow::Result<CostTable> {
     fs::read_to_string(&path)
         .with_context(|| format!("failed to read costs file: {}", path.display()))?