ww: put selected toolchain first in test PATH

selfhost/cmd/ww/main.ww

@@ -1632,6 +1632,88 @@ fn sepallocptrs(cap: i32) ([]*u8 | nomem) = {
 	return value;
 };
 
+type septestenv = struct {
+	values: []str,
+	path: str,
+};
+
+// Pinned cmd/go gives each test binary PATH=$GOROOT/bin:$PATH. The selected
+// WW driver's sibling directory is the local toolchain-bin analogue. Remove
+// normal inherited PATH duplicates because lib/os/exec deliberately preserves
+// the concrete environment array while Go's os/exec keeps the appended value.
+fn sepmaketestenv(toolbin: str, out: *septestenv) bool = {
+	let inherited: []str = os.getenvs();
+	if (inherited.len == SEP_COUNT_MAX) {
+		cerr("ww: cannot prepare test environment\n");
+		return false;
+	};
+	let oldpath: str = "";
+	match (os.getenv("PATH")) {
+	case let value: str => oldpath = value;
+	case void => void;
+	};
+	let total: i64 = 5i64 + (toolbin.len: i64);
+	if (oldpath.len != 0) { total += 1i64 + (oldpath.len: i64); };
+	if (total > SEP_COUNT_MAX: i64) {
+		cerr("ww: cannot prepare test environment\n");
+		return false;
+	};
+	let pathallocation: ([]u8 | nomem) = sepallocbytes(total: i32);
+	let pathbytes: []u8;
+	match (pathallocation) {
+	case let value: []u8 => pathbytes = value;
+	case nomem => {
+		cerr("ww: cannot prepare test environment\n");
+		return false;
+	};
+	};
+	let prefix: str = "PATH=";
+	let i: i32 = 0;
+	for (i < prefix.len) { append(pathbytes, prefix[i]); i += 1; };
+	i = 0;
+	for (i < toolbin.len) { append(pathbytes, toolbin[i]); i += 1; };
+	if (oldpath.len != 0) {
+		append(pathbytes, ':');
+		i = 0;
+		for (i < oldpath.len) { append(pathbytes, oldpath[i]); i += 1; };
+	};
+	let pathenv: str = strings.frombytes(pathbytes);
+	let envallocation: ([]str | nomem) = sepallocstrs(inherited.len + 1);
+	let env: []str;
+	match (envallocation) {
+	case let value: []str => env = value;
+	case nomem => {
+		os.free(pathenv.ptr: *void, pathenv.len: u64);
+		cerr("ww: cannot prepare test environment\n");
+		return false;
+	};
+	};
+	i = 0;
+	let inserted: bool = false;
+	for (i < inherited.len) {
+		if (strings.hasprefix(inherited[i], "PATH=")) {
+			if (!inserted) { append(env, pathenv); inserted = true; };
+		} else {
+			append(env, inherited[i]);
+		};
+		i += 1;
+	};
+	if (!inserted) { append(env, pathenv); };
+	out.values = env;
+	out.path = pathenv;
+	return true;
+};
+
+fn sepfreetestenv(env: *septestenv) void = {
+	if (env.path.ptr != nil && env.path.len != 0) {
+		os.free(env.path.ptr: *void, env.path.len: u64);
+	};
+	if (env.values.ptr != nil && env.values.cap != 0) {
+		os.free(env.values.ptr: *void,
+			(env.values.cap: u64) * (size(str): u64));
+	};
+};
+
 fn sepallocgraph(pkg: []seppkg, context: []sepcontext) (*sepgraph | nomem) = {
 	let emptyfolds: []sepfoldentry;
 	let value: *sepgraph = alloc(sepgraph{
@@ -9186,21 +9268,30 @@ fn runsingletest(selfdir: *u8, src: *u8, incs: *u8, compileonly: i32,
 	if (pattern != nil) {
 		append(execargv, pathstr(pattern));
 	};
-	let env: []str = os.getenvs();
 	let result: exec.result;
-	exec.runstdio(pathstr(outp), execargv, env, &result);
 	let rc: i32 = 1;
-	if (result.termination == exec.termination.EXIT) {
-		rc = result.code;
-	} else { if (result.termination == exec.termination.ERROR) {
-		if (result.code == 127) {
-			cerr("ww: execve failed\n");
-			rc = 127;
-		} else {
-			cerr("ww: process launch/wait failed\n");
-			rc = -1;
-		};
+	let env: septestenv;
+	let toolbin: *u8 = canonicaldir(pathstr(selfdir));
+	if (toolbin == nil) {
+		cerr("ww: cannot prepare test environment\n");
+	} else { if (sepmaketestenv(pathstr(toolbin), &env)) {
+		exec.runstdio(pathstr(outp), execargv, env.values, &result);
+		sepfreetestenv(&env);
+		if (result.termination == exec.termination.EXIT) {
+			rc = result.code;
+		} else { if (result.termination == exec.termination.ERROR) {
+			if (result.code == 127) {
+				cerr("ww: execve failed\n");
+				rc = 127;
+			} else {
+				cerr("ww: process launch/wait failed\n");
+				rc = -1;
+			};
+		}; };
 	}; };
+	if (toolbin != nil) {
+		os.free(toolbin: *void, cstrlen(toolbin) + 1u64);
+	};
 	if (rc == 0 && deferredinstall
 	    && sepinstalltestoutput(outp, outstem) != 0) { rc = 1; };
 	if (owntmp) {