fix: Deno.noColor should not be true when NO_COLOR is empty string (#21275)

Closes https://github.com/denoland/deno/issues/21274

2 files changed, 34 insertions, 2 deletions

diff --git a/cli/tests/unit/tty_color_test.ts b/cli/tests/unit/tty_color_test.ts
index 3adc16b23..b49ffa6bd 100644
--- a/cli/tests/unit/tty_color_test.ts
+++ b/cli/tests/unit/tty_color_test.ts
@@ -24,3 +24,32 @@ Deno.test(
     assertEquals(output, "false\n");
   },
 );
+
+Deno.test(
+  { permissions: { run: true, read: true } },
+  async function denoNoColorTrueEmptyVar() {
+    const { stdout } = await new Deno.Command(Deno.execPath(), {
+      args: ["eval", "console.log(Deno.noColor)"],
+      env: {
+        // https://no-color.org/ -- should not be true when empty
+        NO_COLOR: "",
+      },
+    }).output();
+    const output = new TextDecoder().decode(stdout);
+    assertEquals(output, "false\n");
+  },
+);
+
+Deno.test(
+  { permissions: { run: true, read: true } },
+  async function denoNoColorTrueEmptyVar() {
+    const { stdout } = await new Deno.Command(Deno.execPath(), {
+      args: ["eval", "console.log(Deno.noColor)"],
+      env: {
+        NO_COLOR: "1",
+      },
+    }).output();
+    const output = new TextDecoder().decode(stdout);
+    assertEquals(output, "true\n");
+  },
+);
diff --git a/runtime/colors.rs b/runtime/colors.rs
index fe5a3dcbe..8d915b571 100644
--- a/runtime/colors.rs
+++ b/runtime/colors.rs
@@ -22,8 +22,11 @@ use termcolor::BufferWriter;
 #[cfg(windows)]
 use termcolor::ColorChoice;
 
-static NO_COLOR: Lazy<bool> =
-  Lazy::new(|| std::env::var_os("NO_COLOR").is_some());
+static NO_COLOR: Lazy<bool> = Lazy::new(|| {
+  std::env::var_os("NO_COLOR")
+    .map(|v| !v.is_empty())
+    .unwrap_or(false)
+});
 
 static IS_TTY: Lazy<bool> = Lazy::new(|| std::io::stdout().is_terminal());