addressing PR comments

crates/re_build_tools/src/hashing.rs

@@ -5,6 +5,8 @@ use std::{fs, io};
 use anyhow::Context as _;
 use sha2::{Digest, Sha256};
 
+use crate::{rerun_if_changed, rerun_if_changed_or_doesnt_exist};
+
 // ---
 
 fn encode_hex(bytes: &[u8]) -> String {
@@ -18,7 +20,7 @@ fn encode_hex(bytes: &[u8]) -> String {
 /// Walks the directory at `path` in filename order.
 ///
 /// If `extensions` is specified, only files with the right extensions will be iterated.
-/// Specified extensions should include the dot, e.g. `.fbs`.
+/// Specified extensions should _not_ include the leading dot, e.g. `fbs` rather than `.fbs`.
 pub fn iter_dir<'a>(
     path: impl AsRef<Path>,
     extensions: Option<&'a [&'a str]>,
@@ -28,9 +30,9 @@ pub fn iter_dir<'a>(
         let is_interesting = extensions.map_or(true, |extensions| {
             extensions.iter().any(|ext| {
                 entry
-                    .file_name()
-                    .to_str()
-                    .map_or(false, |s| s.ends_with(ext))
+                    .path()
+                    .extension()
+                    .map_or(false, |ext2| *ext == ext2.to_string_lossy())
             })
         });
         is_dir || is_interesting
@@ -48,6 +50,8 @@ pub fn iter_dir<'a>(
 /// Given a file path, computes the sha256 hash of its contents and returns an hexadecimal string
 /// for it.
 ///
+/// This will automatically emit a `rerun-if-changed` clause for the specified file.
+///
 /// Panics if the file doesn't exist.
 pub fn compute_file_hash(path: impl AsRef<Path>) -> String {
     let mut hasher = Sha256::new();
@@ -60,6 +64,8 @@ pub fn compute_file_hash(path: impl AsRef<Path>) -> String {
         .with_context(|| format!("couldn't copy from {path:?}"))
         .unwrap();
 
+    rerun_if_changed(path);
+
     encode_hex(hasher.finalize().as_slice())
 }
 
@@ -68,8 +74,10 @@ pub fn compute_file_hash(path: impl AsRef<Path>) -> String {
 ///
 /// This includes files in sub-directories (i.e. it's recursive).
 ///
-/// If `extensions` is specified, only files with the right extensions will be hashed.
-/// Specified extensions should include the dot, e.g. `.fbs`.
+/// This will automatically emit a `rerun-if-changed` clause for all the files that were hashed.
+///
+/// If `extensions` is specified, only files with the right extensions will be iterated.
+/// Specified extensions should _not_ include the leading dot, e.g. `fbs` rather than `.fbs`.
 pub fn compute_dir_hash<'a>(path: impl AsRef<Path>, extensions: Option<&'a [&'a str]>) -> String {
     let mut hasher = Sha256::new();
 
@@ -81,6 +89,8 @@ pub fn compute_dir_hash<'a>(path: impl AsRef<Path>, extensions: Option<&'a [&'a
         io::copy(&mut file, &mut hasher)
             .with_context(|| format!("couldn't copy from {filepath:?}"))
             .unwrap();
+
+        rerun_if_changed(path);
     }
 
     encode_hex(hasher.finalize().as_slice())
@@ -90,6 +100,8 @@ pub fn compute_dir_hash<'a>(path: impl AsRef<Path>, extensions: Option<&'a [&'a
 /// returns an hexadecimal string for it.
 ///
 /// This includes the source code of all its direct and indirect dependencies.
+///
+/// This will automatically emit a `rerun-if-changed` clause for all the files that were hashed.
 pub fn compute_crate_hash(pkg_name: impl AsRef<str>) -> String {
     use cargo_metadata::{CargoOpt, MetadataCommand};
     let metadata = MetadataCommand::new()
@@ -126,6 +138,9 @@ pub fn compute_strings_hash(strs: &[&str]) -> String {
 
 /// Writes the given `hash` at the specified `path`.
 ///
+/// `hash` should have been computed using of the methods in this module: [`compute_file_hash`],
+/// [`compute_dir_hash`], [`compute_crate_hash`].
+///
 /// Panics on I/O errors.
 ///
 /// Use [`read_versioning_hash`] to read it back.
@@ -148,9 +163,16 @@ pub fn write_versioning_hash(path: impl AsRef<Path>, hash: impl AsRef<str>) {
 
 /// Reads back a versioning hash that was written with [`write_versioning_hash`].
 ///
+/// This will automatically emit a `rerun-if-changed` clause for the specified filepath.
+///
 /// Returns `None` on error.
 pub fn read_versioning_hash(path: impl AsRef<Path>) -> Option<String> {
     let path = path.as_ref();
+
+    // NOTE: It's important we trigger if the file doesn't exist, as this means the user explicitly
+    // deleted the versioning file, i.e. they're trying to force a rebuild.
+    rerun_if_changed_or_doesnt_exist(path);
+
     std::fs::read_to_string(path).ok().and_then(|contents| {
         contents
             .lines()