use write_if_changed utils

.changes/avoid-rebuilds.md

@@ -0,0 +1,7 @@
+---
+"tauri": patch:bug
+"tauri-build": patch:bug
+"tauri-utils": patch:bug
+---
+
+Prevent build script from rerunning unnecessarily by only writing files when the content changes.

core/tauri-acl-schema/build.rs

@@ -6,9 +6,8 @@ use std::{error::Error, path::PathBuf};
 
 use schemars::schema_for;
 use tauri_utils::{
-  acl::capability::Capability,
-  acl::{Permission, Scopes},
-  write_if_changed,
+  acl::{capability::Capability, Permission, Scopes},
+  io::write_if_changed,
 };
 
 macro_rules! schema {
@@ -27,7 +26,7 @@ pub fn main() -> Result<(), Box<dyn Error>> {
   let out = PathBuf::from(std::env::var("CARGO_MANIFEST_DIR")?);
   for (filename, schema) in schemas {
     let schema = serde_json::to_string_pretty(&schema)?;
-    write_if_changed(out.join(filename), schema)?;
+    write_if_changed(&schema, &out.join(filename))?;
   }
 
   Ok(())

core/tauri-build/src/acl.rs

@@ -23,6 +23,7 @@ use tauri_utils::{
     manifest::Manifest,
     APP_ACL_KEY,
   },
+  io::write_if_changed,
   platform::Target,
 };
 
@@ -384,7 +385,8 @@ permissions = [{default_permissions}]
 
         let default_permission_toml_path = plugin_out_dir.join("default.toml");
 
-        write_if_changed(&default_permission_toml, &default_permission_toml_path);
+        write_if_changed(&default_permission_toml, &default_permission_toml_path)
+          .unwrap_or_else(|_| panic!("unable to autogenerate {default_permission_toml_path:?}"));
       }
 
       tauri_utils::acl::build::define_permissions(
@@ -428,12 +430,6 @@ permissions = [{default_permissions}]
   Ok(acl_manifests)
 }
 
-fn write_if_changed(content: &str, path: &Path) {
-  if content != read_to_string(path).unwrap_or_default() {
-    std::fs::write(path, content).unwrap_or_else(|_| panic!("unable to autogenerate {path:?}"));
-  }
-}
-
 pub fn app_manifest_permissions(
   out_dir: &Path,
   manifest: AppManifest,

core/tauri-build/src/mobile.rs

@@ -6,7 +6,7 @@ use std::{fs::write, path::PathBuf};
 
 use anyhow::{Context, Result};
 use semver::Version;
-use tauri_utils::config::Config;
+use tauri_utils::{config::Config, io::write_if_changed};
 
 use crate::is_dev;
 
@@ -81,21 +81,11 @@ dependencies {"
   }
 
   // Overwrite only if changed to not trigger rebuilds
-  if std::fs::read_to_string(&gradle_settings_path)
-    .map(|o| o != gradle_settings)
-    .unwrap_or(true)
-  {
-    write(&gradle_settings_path, gradle_settings)
-      .context("failed to write tauri.settings.gradle")?;
-  }
+  write_if_changed(&gradle_settings, &gradle_settings_path)
+    .context("failed to write tauri.settings.gradle")?;
 
-  if std::fs::read_to_string(&app_build_gradle_path)
-    .map(|o| o != app_build_gradle)
-    .unwrap_or(true)
-  {
-    write(&app_build_gradle_path, app_build_gradle)
-      .context("failed to write tauri.build.gradle.kts")?;
-  }
+  write_if_changed(&app_build_gradle, &app_build_gradle_path)
+    .context("failed to write tauri.build.gradle.kts")?;
 
   if !app_tauri_properties.is_empty() {
     let app_tauri_properties_content = format!(

core/tauri-utils/src/acl/build.rs

@@ -11,7 +11,7 @@ use std::{
   path::{Path, PathBuf},
 };
 
-use crate::acl::Error;
+use crate::{acl::Error, io::write_if_changed};
 use schemars::{
   schema::{InstanceType, Metadata, RootSchema, Schema, SchemaObject, SubschemaValidation},
   schema_for,
@@ -450,7 +450,8 @@ commands.deny = ["{command}"]
     );
 
     let out_path = path.join(format!("{command}.toml"));
-    write_if_changed(&toml, &out_path);
+    write_if_changed(&toml, &out_path)
+      .unwrap_or_else(|_| panic!("unable to autogenerate {out_path:?}"));
 
     autogenerated
       .allowed
@@ -462,9 +463,3 @@ commands.deny = ["{command}"]
 
   autogenerated
 }
-
-fn write_if_changed(content: &str, path: &Path) {
-  if content != read_to_string(path).unwrap_or_default() {
-    std::fs::write(path, content).unwrap_or_else(|_| panic!("unable to autogenerate {path:?}"));
-  }
-}

core/tauri-utils/src/io.rs

@@ -4,7 +4,16 @@
 
 //! IO helpers.
 
-use std::io::BufRead;
+use std::{fs::read_to_string, io::BufRead, path::Path};
+
+/// Write to the given file if the content is different.
+pub fn write_if_changed(content: &str, path: &Path) -> std::io::Result<()> {
+  if content != read_to_string(path).unwrap_or_default() {
+    std::fs::write(path, content)
+  } else {
+    Ok(())
+  }
+}
 
 /// Read all bytes until a newline (the `0xA` byte) or a carriage return (`\r`) is reached, and append them to the provided buffer.
 ///

core/tauri/build.rs

@@ -3,12 +3,12 @@
 // SPDX-License-Identifier: MIT
 
 use heck::AsShoutySnakeCase;
+use tauri_utils::io::write_if_changed;
 
 use std::env::var_os;
 use std::fs::create_dir_all;
 use std::fs::read_dir;
 use std::fs::read_to_string;
-use std::fs::write;
 use std::{
   env::var,
   path::{Path, PathBuf},
@@ -290,12 +290,8 @@ fn main() {
 
         let out_path = kotlin_out_dir.join(file.file_name());
         // Overwrite only if changed to not trigger rebuilds
-        if std::fs::read_to_string(&out_path)
-          .map(|o| o != content)
-          .unwrap_or(true)
-        {
-          write(&out_path, content).expect("Failed to write kotlin file");
-        }
+        write_if_changed(&content, &out_path).expect("Failed to write kotlin file");
+
         println!("cargo:rerun-if-changed={}", out_path.display());
       }
     }