feat(forge build): cache project selectors by default

crates/cli/src/utils/cmd.rs

@@ -440,7 +440,10 @@ pub async fn print_traces(
 
 /// Traverse the artifacts in the project to generate local signatures and merge them into the cache
 /// file.
-pub fn cache_local_signatures(output: &ProjectCompileOutput, cache_dir: &Path) -> Result<()> {
+pub fn cache_local_signatures(output: &ProjectCompileOutput) -> Result<()> {
+    let Some(cache_dir) = Config::foundry_cache_dir() else {
+        eyre::bail!("Failed to get `cache_dir` to generate local signatures.");
+    };
     let path = cache_dir.join("signatures");
     let mut signatures = SignaturesCache::load(&path);
     for (_, artifact) in output.artifacts() {

crates/forge/src/cmd/build.rs

@@ -1,7 +1,10 @@
 use super::{install, watch::WatchArgs};
 use clap::Parser;
 use eyre::Result;
-use foundry_cli::{opts::BuildOpts, utils::LoadConfig};
+use foundry_cli::{
+    opts::BuildOpts,
+    utils::{cache_local_signatures, LoadConfig},
+};
 use foundry_common::{compile::ProjectCompiler, shell};
 use foundry_compilers::{
     compilers::{multi::MultiCompilerLanguage, Language},
@@ -100,6 +103,9 @@ impl BuildArgs {
 
         let output = compiler.compile(&project)?;
 
+        // Cache project selectors.
+        cache_local_signatures(&output)?;
+
         if format_json && !self.names && !self.sizes {
             sh_println!("{}", serde_json::to_string_pretty(&output.output())?)?;
         }

crates/forge/src/cmd/selectors.rs

@@ -11,7 +11,6 @@ use foundry_common::{
     selectors::{import_selectors, SelectorImportData},
 };
 use foundry_compilers::{artifacts::output_selection::ContractOutputSelection, info::ContractInfo};
-use foundry_config::Config;
 use std::fs::canonicalize;
 
 /// CLI arguments for `forge selectors`.
@@ -95,7 +94,7 @@ impl SelectorsSubcommands {
                 // compile the project to get the artifacts/abis
                 let project = build_args.project()?;
                 let outcome = ProjectCompiler::new().quiet(true).compile(&project)?;
-                cache_local_signatures(&outcome, &Config::foundry_cache_dir().unwrap())?
+                cache_local_signatures(&outcome)?;
             }
             Self::Upload { contract, all, project_paths } => {
                 let build_args = BuildOpts {

crates/forge/tests/cli/test_cmd.rs

@@ -3828,3 +3828,41 @@ Encountered a total of 1 failing tests, 0 tests succeeded
 
 "#]]);
 });
+
+// This test is a copy of `error_event_decode_with_cache` in cast/tests/cli/selectors.rs
+// but it uses `forge build` to check that the project selectors are cached by default.
+forgetest_init!(build_with_selectors_cache, |prj, cmd| {
+    prj.add_source(
+        "LocalProjectContract",
+        r#"
+contract ContractWithCustomError {
+    error AnotherValueTooHigh(uint256, address);
+    event MyUniqueEventWithinLocalProject(uint256 a, address b);
+}
+   "#,
+    )
+    .unwrap();
+    // Build and cache project selectors.
+    cmd.forge_fuse().args(["build"]).assert_success();
+
+    // Assert cast can decode custom error with local cache.
+    cmd.cast_fuse()
+        .args(["decode-error", "0x7191bc6200000000000000000000000000000000000000000000000000000000000000650000000000000000000000000000000000000000000000000000000000D0004F"])
+        .assert_success()
+        .stdout_eq(str![[r#"
+AnotherValueTooHigh(uint256,address)
+101
+0x0000000000000000000000000000000000D0004F
+
+"#]]);
+    // Assert cast can decode event with local cache.
+    cmd.cast_fuse()
+        .args(["decode-event", "0xbd3699995dcc867b64dbb607be2c33be38df9134bef1178df13bfb9446e73104000000000000000000000000000000000000000000000000000000000000004e00000000000000000000000000000000000000000000000000000dd00000004e"])
+        .assert_success()
+        .stdout_eq(str![[r#"
+MyUniqueEventWithinLocalProject(uint256,address)
+78
+0x00000000000000000000000000000DD00000004e
+
+"#]]);
+});