tests: check file size instead of content sha in purge_caches

Hashing all the files in the workspace was taking a lot of time (around
40 seconds on my computer, with a NVMe disk), significantly slowing down
the amount of time needed for running the tests.

This commit switches to comparing file sizes, as after all we only care
about the workspace size not increasing when purging all caches.

Author: pietroalbini

Cargo.toml

@@ -45,4 +45,3 @@ getrandom = { version = "0.1.12", features = ["std"] }
 [dev-dependencies]
 env_logger = "0.6.1"
 tiny_http = "0.7.0"
-sha1 = "0.6.0"

tests/integration/purge_caches.rs

@@ -1,7 +1,6 @@
 use failure::Error;
 use rustwide::cmd::SandboxBuilder;
 use rustwide::{Crate, Toolchain};
-use sha1::{Digest, Sha1};
 use std::collections::HashMap;
 use std::path::{Path, PathBuf};
 
@@ -74,7 +73,7 @@ fn should_ignore(base: &Path, path: &Path) -> bool {
 #[derive(Debug, PartialEq, Eq)]
 struct WorkspaceContents {
     base: PathBuf,
-    files: HashMap<PathBuf, Digest>,
+    files: HashMap<PathBuf, u64>,
 }
 
 impl WorkspaceContents {
@@ -83,14 +82,13 @@ impl WorkspaceContents {
 
         for entry in walkdir::WalkDir::new(path) {
             let entry = entry?;
-            if !entry.metadata()?.is_file() {
+            let metadata = entry.metadata()?;
+
+            if !metadata.is_file() {
                 continue;
             }
 
-            let mut sha = Sha1::new();
-            sha.update(&std::fs::read(entry.path())?);
-
-            files.insert(entry.path().into(), sha.digest());
+            files.insert(entry.path().into(), metadata.len());
         }
 
         Ok(Self {
@@ -111,7 +109,7 @@ impl WorkspaceContents {
 
             if let Some(end_digest) = other.files.remove(&path) {
                 if start_digest != end_digest {
-                    println!("file {} changed", path.display());
+                    println!("file {} changed its size", path.display());
                     same = false;
                 }
             } else {