fix #3027: live reload SSE when outdir is /

CHANGELOG.md

@@ -57,6 +57,10 @@
     foo(1e3.x,0 .x,.1.x,1e-4.x,0xffff0000ffff0000.x);
     ```
 
+* Fix server-sent events with live reload when writing to the file system root ([#3027](https://github.com/evanw/esbuild/issues/3027))
+
+    This release fixes a bug where esbuild previously failed to emit server-sent events for live reload when `outdir` was the file system root, such as `/`. This happened because `/` is the only path on Unix that cannot have a trailing slash trimmed from it, which was fixed by improved path handling.
+
 ## 0.17.14
 
 * Allow the TypeScript 5.0 `const` modifier in object type declarations ([#3021](https://github.com/evanw/esbuild/issues/3021))

Makefile

@@ -40,7 +40,7 @@ check-go-version:
 # variable like this: "ESBUILD_RACE=-race make test". Or you can permanently
 # enable it by adding "export ESBUILD_RACE=-race" to your shell profile.
 test-go:
-	go test $(ESBUILD_RACE) ./internal/...
+	go test $(ESBUILD_RACE) ./internal/... ./pkg/...
 
 vet-go:
 	go vet ./cmd/... ./internal/... ./pkg/...

pkg/api/api_impl.go

@@ -2445,3 +2445,38 @@ func summarizeOutputFiles(outputFiles []OutputFile) buildSummary {
 	}
 	return summary
 }
+
+func stripDirPrefix(path string, prefix string, allowedSlashes string) (string, bool) {
+	if strings.HasPrefix(path, prefix) {
+		pathLen := len(path)
+		prefixLen := len(prefix)
+
+		// Just return the path if there is no prefix
+		if prefixLen == 0 {
+			return path, true
+		}
+
+		// Return the empty string if the path equals the prefix
+		if pathLen == prefixLen {
+			return "", true
+		}
+
+		if strings.IndexByte(allowedSlashes, prefix[prefixLen-1]) >= 0 {
+			// Return the suffix if the prefix ends in a slash. Examples:
+			//
+			//   stripDirPrefix(`/foo`, `/`, `/`) => `foo`
+			//   stripDirPrefix(`C:\foo`, `C:\`, `\/`) => `foo`
+			//
+			return path[prefixLen:], true
+		} else if strings.IndexByte(allowedSlashes, path[prefixLen]) >= 0 {
+			// Return the suffix if there's a slash after the prefix. Examples:
+			//
+			//   stripDirPrefix(`/foo/bar`, `/foo`, `/`) => `bar`
+			//   stripDirPrefix(`C:\foo\bar`, `C:\foo`, `\/`) => `bar`
+			//
+			return path[prefixLen+1:], true
+		}
+	}
+
+	return "", false
+}

pkg/api/api_impl_test.go

@@ -0,0 +1,57 @@
+package api
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/evanw/esbuild/internal/test"
+)
+
+func TestStripDirPrefix(t *testing.T) {
+	expectSuccess := func(path string, prefix string, allowedSlashes string, expected string) {
+		t.Helper()
+		t.Run(fmt.Sprintf("path=%s prefix=%s slashes=%s", path, prefix, allowedSlashes), func(t *testing.T) {
+			t.Helper()
+			observed, ok := stripDirPrefix(path, prefix, allowedSlashes)
+			if !ok {
+				t.Fatalf("Unexpected failure")
+			}
+			test.AssertEqualWithDiff(t, observed, expected)
+		})
+	}
+
+	expectFailure := func(path string, prefix string, allowedSlashes string) {
+		t.Helper()
+		t.Run(fmt.Sprintf("path=%s prefix=%s slashes=%s", path, prefix, allowedSlashes), func(t *testing.T) {
+			t.Helper()
+			_, ok := stripDirPrefix(path, prefix, allowedSlashes)
+			if ok {
+				t.Fatalf("Unexpected success")
+			}
+		})
+	}
+
+	// Note: People sometimes set "outdir" to "/" and expect that to work:
+	// https://github.com/evanw/esbuild/issues/3027
+
+	expectSuccess(`/foo/bar/baz`, ``, `/`, `/foo/bar/baz`)
+	expectSuccess(`/foo/bar/baz`, `/`, `/`, `foo/bar/baz`)
+	expectSuccess(`/foo/bar/baz`, `/foo`, `/`, `bar/baz`)
+	expectSuccess(`/foo/bar/baz`, `/foo/bar`, `/`, `baz`)
+	expectSuccess(`/foo/bar/baz`, `/foo/bar/baz`, `/`, ``)
+	expectSuccess(`/foo/bar//baz`, `/foo/bar`, `/`, `/baz`)
+	expectSuccess(`C:\foo\bar\baz`, ``, `\/`, `C:\foo\bar\baz`)
+	expectSuccess(`C:\foo\bar\baz`, `C:`, `\/`, `foo\bar\baz`)
+	expectSuccess(`C:\foo\bar\baz`, `C:\`, `\/`, `foo\bar\baz`)
+	expectSuccess(`C:\foo\bar\baz`, `C:\foo`, `\/`, `bar\baz`)
+	expectSuccess(`C:\foo\bar\baz`, `C:\foo\bar`, `\/`, `baz`)
+	expectSuccess(`C:\foo\bar\baz`, `C:\foo\bar\baz`, `\/`, ``)
+	expectSuccess(`C:\foo\bar\\baz`, `C:\foo\bar`, `\/`, `\baz`)
+	expectSuccess(`C:\foo\bar/baz`, `C:\foo\bar`, `\/`, `baz`)
+