obey builddir for placing .n2_db

src/db.rs

@@ -12,6 +12,7 @@ use std::io::BufReader;
 use std::io::Read;
 use std::io::Write;
 use std::mem::MaybeUninit;
+use std::path::Path;
 
 const VERSION: u32 = 1;
 
@@ -111,7 +112,7 @@ pub struct Writer {
 }
 
 impl Writer {
-    fn create(path: &str) -> std::io::Result<Self> {
+    fn create(path: &Path) -> std::io::Result<Self> {
         let f = std::fs::File::create(path)?;
         let mut w = Writer {
             ids: IdMap::default(),
@@ -333,7 +334,7 @@ impl<'a> Reader<'a> {
 }
 
 /// Opens or creates an on-disk database, loading its state into the provided Graph.
-pub fn open(path: &str, graph: &mut Graph, hashes: &mut Hashes) -> anyhow::Result<Writer> {
+pub fn open(path: &Path, graph: &mut Graph, hashes: &mut Hashes) -> anyhow::Result<Writer> {
     match std::fs::OpenOptions::new()
         .read(true)
         .append(true)

src/load.rs

@@ -8,9 +8,9 @@ use crate::{
     {db, eval, graph, parse, trace},
 };
 use anyhow::{anyhow, bail};
-use std::borrow::Cow;
 use std::collections::HashMap;
 use std::path::PathBuf;
+use std::{borrow::Cow, path::Path};
 
 /// A variable lookup environment for magic $in/$out variables.
 struct BuildImplicitVars<'a> {
@@ -49,6 +49,7 @@ struct Loader {
     /// rule name -> list of (key, val)
     rules: HashMap<String, SmallMap<String, eval::EvalString<String>>>,
     pools: SmallMap<String, usize>,
+    builddir: Option<String>,
 }
 
 impl parse::Loader for Loader {
@@ -196,6 +197,7 @@ impl Loader {
                 }
             };
         }
+        self.builddir = parser.vars.get("builddir").cloned();
         Ok(())
     }
 }
@@ -221,7 +223,14 @@ pub fn read(build_filename: &str) -> anyhow::Result<State> {
     })?;
     let mut hashes = graph::Hashes::default();
     let db = trace::scope("db::open", || {
-        db::open(".n2_db", &mut loader.graph, &mut hashes)
+        let mut db_path = PathBuf::from(".n2_db");
+        if let Some(builddir) = &loader.builddir {
+            db_path = Path::new(&builddir).join(db_path);
+            if let Some(parent) = db_path.parent() {
+                std::fs::create_dir_all(parent)?;
+            }
+        };
+        db::open(&db_path, &mut loader.graph, &mut hashes)
     })
     .map_err(|err| anyhow!("load .n2_db: {}", err))?;
     Ok(State {

tests/e2e/basic.rs

@@ -312,3 +312,22 @@ build out3: phony out2
     space.read("outfile")?;
     Ok(())
 }
+
+// builddir controls where .n2_db is written.
+#[test]
+fn builddir() -> anyhow::Result<()> {
+    let space = TestSpace::new()?;
+    space.write(
+        "build.ninja",
+        &[
+            "builddir = foo",
+            TOUCH_RULE,
+            "build $builddir/bar: touch",
+            "",
+        ]
+        .join("\n"),
+    )?;
+    space.run_expect(&mut n2_command(vec!["foo/bar"]))?;
+    space.read("foo/.n2_db")?;
+    Ok(())
+}