From da415708c44dd0eaccdd1848bcdce334462ec0d7 Mon Sep 17 00:00:00 2001
From: Dan Bjorge <dan.bjorge@deque.com>
Date: Wed, 14 Jan 2026 16:05:04 -0800
Subject: [PATCH 1/2] feat: add comment support for .nvmrc files

Implements comment stripping for .nvmrc files following nvm v0.40.0 behavior.
Comments (anything after #) are now stripped from .nvmrc files, supporting
both inline comments and full-line comments. Leaves .node-version parsing
as-is.

Changes:
- Add nvmrc.rs module for .nvmrc parsing with comment support
- Refactor format detection to version_file_format.rs
- Add unit tests for comment stripping and format detection
- Add E2E tests for various comment scenarios

Fixes: #1209
---
 .changeset/mighty-pots-fetch.md               |   5 +
 e2e/__snapshots__/nvmrc-comments.test.ts.snap | 247 ++++++++++++++++++
 e2e/nvmrc-comments.test.ts                    |  86 ++++++
 src/main.rs                                   |   2 +
 src/nvmrc.rs                                  | 128 +++++++++
 src/version_file_format.rs                    |  60 +++++
 src/version_files.rs                          |  36 ++-
 7 files changed, 552 insertions(+), 12 deletions(-)
 create mode 100644 .changeset/mighty-pots-fetch.md
 create mode 100644 e2e/__snapshots__/nvmrc-comments.test.ts.snap
 create mode 100644 e2e/nvmrc-comments.test.ts
 create mode 100644 src/nvmrc.rs
 create mode 100644 src/version_file_format.rs

diff --git a/.changeset/mighty-pots-fetch.md b/.changeset/mighty-pots-fetch.md
new file mode 100644
index 000000000..e20c3b3a3
--- /dev/null
+++ b/.changeset/mighty-pots-fetch.md
@@ -0,0 +1,5 @@
+---
+"fnm": minor
+---
+
+support comments in .nvmrc files
diff --git a/e2e/__snapshots__/nvmrc-comments.test.ts.snap b/e2e/__snapshots__/nvmrc-comments.test.ts.snap
new file mode 100644
index 000000000..b364a57be
--- /dev/null
+++ b/e2e/__snapshots__/nvmrc-comments.test.ts.snap
@@ -0,0 +1,247 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`Bash .node-version should not strip comments: Bash 1`] = `
+"set -e
+eval "$(fnm env)"
+fnm install
+fnm use
+if [ "$(node --version)" != "v8.11.3" ]; then
+  echo "Expected node version to be v8.11.3. Got $(node --version)"
+  exit 1
+fi"
+`;
+
+exports[`Bash .nvmrc with comment on first line: Bash 1`] = `
+"set -e
+eval "$(fnm env)"
+fnm install
+fnm use
+if [ "$(node --version)" != "v8.11.3" ]; then
+  echo "Expected node version to be v8.11.3. Got $(node --version)"
+  exit 1
+fi"
+`;
+
+exports[`Bash .nvmrc with empty lines and comments: Bash 1`] = `
+"set -e
+eval "$(fnm env)"
+fnm install
+fnm use
+if [ "$(node --version)" != "v8.11.3" ]; then
+  echo "Expected node version to be v8.11.3. Got $(node --version)"
+  exit 1
+fi"
+`;
+
+exports[`Bash .nvmrc with inline comment after version: Bash 1`] = `
+"set -e
+eval "$(fnm env)"
+fnm install
+fnm use
+if [ "$(node --version)" != "v8.11.3" ]; then
+  echo "Expected node version to be v8.11.3. Got $(node --version)"
+  exit 1
+fi"
+`;
+
+exports[`Bash .nvmrc with multiple comment lines: Bash 1`] = `
+"set -e
+eval "$(fnm env)"
+fnm install
+fnm use
+if [ "$(node --version)" != "v8.11.3" ]; then
+  echo "Expected node version to be v8.11.3. Got $(node --version)"
+  exit 1
+fi"
+`;
+
+exports[`Bash .nvmrc with whitespace and inline comments: Bash 1`] = `
+"set -e
+eval "$(fnm env)"
+fnm install
+fnm use
+if [ "$(node --version)" != "v8.11.3" ]; then
+  echo "Expected node version to be v8.11.3. Got $(node --version)"
+  exit 1
+fi"
+`;
+
+exports[`Fish .node-version should not strip comments: Fish 1`] = `
+"fnm env | source
+fnm install
+fnm use
+set ____test____ (node --version)
+if test "$____test____" != "v8.11.3"
+  echo "Expected node version to be v8.11.3. Got $____test____"
+  exit 1
+end"
+`;
+
+exports[`Fish .nvmrc with comment on first line: Fish 1`] = `
+"fnm env | source
+fnm install
+fnm use
+set ____test____ (node --version)
+if test "$____test____" != "v8.11.3"
+  echo "Expected node version to be v8.11.3. Got $____test____"
+  exit 1
+end"
+`;
+
+exports[`Fish .nvmrc with empty lines and comments: Fish 1`] = `
+"fnm env | source
+fnm install
+fnm use
+set ____test____ (node --version)
+if test "$____test____" != "v8.11.3"
+  echo "Expected node version to be v8.11.3. Got $____test____"
+  exit 1
+end"
+`;
+
+exports[`Fish .nvmrc with inline comment after version: Fish 1`] = `
+"fnm env | source
+fnm install
+fnm use
+set ____test____ (node --version)
+if test "$____test____" != "v8.11.3"
+  echo "Expected node version to be v8.11.3. Got $____test____"
+  exit 1
+end"
+`;
+
+exports[`Fish .nvmrc with multiple comment lines: Fish 1`] = `
+"fnm env | source
+fnm install
+fnm use
+set ____test____ (node --version)
+if test "$____test____" != "v8.11.3"
+  echo "Expected node version to be v8.11.3. Got $____test____"
+  exit 1
+end"
+`;
+
+exports[`Fish .nvmrc with whitespace and inline comments: Fish 1`] = `
+"fnm env | source
+fnm install
+fnm use
+set ____test____ (node --version)
+if test "$____test____" != "v8.11.3"
+  echo "Expected node version to be v8.11.3. Got $____test____"
+  exit 1
+end"
+`;
+
+exports[`PowerShell .node-version should not strip comments: PowerShell 1`] = `
+"$ErrorActionPreference = "Stop"
+fnm env | Out-String | Invoke-Expression
+fnm install
+fnm use
+if ( "$(node --version)" -ne "v8.11.3" ) { echo "Expected node version to be v8.11.3. Got $(node --version)"; exit 1 }"
+`;
+
+exports[`PowerShell .nvmrc with comment on first line: PowerShell 1`] = `
+"$ErrorActionPreference = "Stop"
+fnm env | Out-String | Invoke-Expression
+fnm install
+fnm use
+if ( "$(node --version)" -ne "v8.11.3" ) { echo "Expected node version to be v8.11.3. Got $(node --version)"; exit 1 }"
+`;
+
+exports[`PowerShell .nvmrc with empty lines and comments: PowerShell 1`] = `
+"$ErrorActionPreference = "Stop"
+fnm env | Out-String | Invoke-Expression
+fnm install
+fnm use
+if ( "$(node --version)" -ne "v8.11.3" ) { echo "Expected node version to be v8.11.3. Got $(node --version)"; exit 1 }"
+`;
+
+exports[`PowerShell .nvmrc with inline comment after version: PowerShell 1`] = `
+"$ErrorActionPreference = "Stop"
+fnm env | Out-String | Invoke-Expression
+fnm install
+fnm use
+if ( "$(node --version)" -ne "v8.11.3" ) { echo "Expected node version to be v8.11.3. Got $(node --version)"; exit 1 }"
+`;
+
+exports[`PowerShell .nvmrc with multiple comment lines: PowerShell 1`] = `
+"$ErrorActionPreference = "Stop"
+fnm env | Out-String | Invoke-Expression
+fnm install
+fnm use
+if ( "$(node --version)" -ne "v8.11.3" ) { echo "Expected node version to be v8.11.3. Got $(node --version)"; exit 1 }"
+`;
+
+exports[`PowerShell .nvmrc with whitespace and inline comments: PowerShell 1`] = `
+"$ErrorActionPreference = "Stop"
+fnm env | Out-String | Invoke-Expression
+fnm install
+fnm use
+if ( "$(node --version)" -ne "v8.11.3" ) { echo "Expected node version to be v8.11.3. Got $(node --version)"; exit 1 }"
+`;
+
+exports[`Zsh .node-version should not strip comments: Zsh 1`] = `
+"set -e
+eval "$(fnm env)"
+fnm install
+fnm use
+if [ "$(node --version)" != "v8.11.3" ]; then
+  echo "Expected node version to be v8.11.3. Got $(node --version)"
+  exit 1
+fi"
+`;
+
+exports[`Zsh .nvmrc with comment on first line: Zsh 1`] = `
+"set -e
+eval "$(fnm env)"
+fnm install
+fnm use
+if [ "$(node --version)" != "v8.11.3" ]; then
+  echo "Expected node version to be v8.11.3. Got $(node --version)"
+  exit 1
+fi"
+`;
+
+exports[`Zsh .nvmrc with empty lines and comments: Zsh 1`] = `
+"set -e
+eval "$(fnm env)"
+fnm install
+fnm use
+if [ "$(node --version)" != "v8.11.3" ]; then
+  echo "Expected node version to be v8.11.3. Got $(node --version)"
+  exit 1
+fi"
+`;
+
+exports[`Zsh .nvmrc with inline comment after version: Zsh 1`] = `
+"set -e
+eval "$(fnm env)"
+fnm install
+fnm use
+if [ "$(node --version)" != "v8.11.3" ]; then
+  echo "Expected node version to be v8.11.3. Got $(node --version)"
+  exit 1
+fi"
+`;
+
+exports[`Zsh .nvmrc with multiple comment lines: Zsh 1`] = `
+"set -e
+eval "$(fnm env)"
+fnm install
+fnm use
+if [ "$(node --version)" != "v8.11.3" ]; then
+  echo "Expected node version to be v8.11.3. Got $(node --version)"
+  exit 1
+fi"
+`;
+
+exports[`Zsh .nvmrc with whitespace and inline comments: Zsh 1`] = `
+"set -e
+eval "$(fnm env)"
+fnm install
+fnm use
+if [ "$(node --version)" != "v8.11.3" ]; then
+  echo "Expected node version to be v8.11.3. Got $(node --version)"
+  exit 1
+fi"
+`;
diff --git a/e2e/nvmrc-comments.test.ts b/e2e/nvmrc-comments.test.ts
new file mode 100644
index 000000000..50cd836a4
--- /dev/null
+++ b/e2e/nvmrc-comments.test.ts
@@ -0,0 +1,86 @@
+import { writeFile } from "node:fs/promises"
+import { join } from "node:path"
+import { script } from "./shellcode/script.js"
+import { Bash, Fish, PowerShell, WinCmd, Zsh } from "./shellcode/shells.js"
+import testCwd from "./shellcode/test-cwd.js"
+import testNodeVersion from "./shellcode/test-node-version.js"
+import describe from "./describe.js"
+
+for (const shell of [Bash, Zsh, Fish, PowerShell, WinCmd]) {
+  describe(shell, () => {
+    test(`.nvmrc with comment on first line`, async () => {
+      await writeFile(join(testCwd(), ".nvmrc"), "# comment\nv8.11.3")
+      await script(shell)
+        .then(shell.env({}))
+        .then(shell.call("fnm", ["install"]))
+        .then(shell.call("fnm", ["use"]))
+        .then(testNodeVersion(shell, "v8.11.3"))
+        .takeSnapshot(shell)
+        .execute(shell)
+    })
+
+    test(`.nvmrc with inline comment after version`, async () => {
+      await writeFile(join(testCwd(), ".nvmrc"), "v8.11.3 # this is Node 8 LTS")
+      await script(shell)
+        .then(shell.env({}))
+        .then(shell.call("fnm", ["install"]))
+        .then(shell.call("fnm", ["use"]))
+        .then(testNodeVersion(shell, "v8.11.3"))
+        .takeSnapshot(shell)
+        .execute(shell)
+    })
+
+    test(`.nvmrc with multiple comment lines`, async () => {
+      await writeFile(
+        join(testCwd(), ".nvmrc"),
+        "# First comment\n# Second comment\n\nv8.11.3\n# Trailing comment",
+      )
+      await script(shell)
+        .then(shell.env({}))
+        .then(shell.call("fnm", ["install"]))
+        .then(shell.call("fnm", ["use"]))
+        .then(testNodeVersion(shell, "v8.11.3"))
+        .takeSnapshot(shell)
+        .execute(shell)
+    })
+
+    test(`.nvmrc with empty lines and comments`, async () => {
+      await writeFile(
+        join(testCwd(), ".nvmrc"),
+        "\n\n# comment\n\nv8.11.3\n\n# another comment",
+      )
+      await script(shell)
+        .then(shell.env({}))
+        .then(shell.call("fnm", ["install"]))
+        .then(shell.call("fnm", ["use"]))
+        .then(testNodeVersion(shell, "v8.11.3"))
+        .takeSnapshot(shell)
+        .execute(shell)
+    })
+
+    test(`.nvmrc with whitespace and inline comments`, async () => {
+      await writeFile(
+        join(testCwd(), ".nvmrc"),
+        "  # comment with spaces  \n  v8.11.3  # inline comment  ",
+      )
+      await script(shell)
+        .then(shell.env({}))
+        .then(shell.call("fnm", ["install"]))
+        .then(shell.call("fnm", ["use"]))
+        .then(testNodeVersion(shell, "v8.11.3"))
+        .takeSnapshot(shell)
+        .execute(shell)
+    })
+
+    test(`.node-version should not strip comments`, async () => {
+      await writeFile(join(testCwd(), ".node-version"), "v8.11.3")
+      await script(shell)
+        .then(shell.env({}))
+        .then(shell.call("fnm", ["install"]))
+        .then(shell.call("fnm", ["use"]))
+        .then(testNodeVersion(shell, "v8.11.3"))
+        .takeSnapshot(shell)
+        .execute(shell)
+    })
+  })
+}
diff --git a/src/main.rs b/src/main.rs
index 6ab10eab5..cd3e68a96 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -20,6 +20,7 @@ mod fs;
 mod http;
 mod installed_versions;
 mod lts;
+mod nvmrc;
 mod package_json;
 mod path_ext;
 mod progress;
@@ -30,6 +31,7 @@ mod system_version;
 mod user_version;
 mod user_version_reader;
 mod version;
+mod version_file_format;
 mod version_file_strategy;
 mod version_files;
 
diff --git a/src/nvmrc.rs b/src/nvmrc.rs
new file mode 100644
index 000000000..405a45d0e
--- /dev/null
+++ b/src/nvmrc.rs
@@ -0,0 +1,128 @@
+use crate::user_version::UserVersion;
+use std::str::FromStr;
+
+pub struct Nvmrc {
+    content: String,
+}
+
+impl Nvmrc {
+    pub fn parse(content: String) -> Option<Self> {
+        Some(Self { content })
+    }
+
+    pub fn version(self) -> Option<UserVersion> {
+        let cleaned = Self::strip_comments(&self.content);
+        if cleaned.is_empty() {
+            return None;
+        }
+        UserVersion::from_str(&cleaned).ok()
+    }
+
+    fn strip_comments(content: &str) -> String {
+        content
+            .lines()
+            .map(|line| {
+                // Remove everything after # (including #)
+                line.split('#').next().unwrap_or("")
+            })
+            .map(|line| line.trim())
+            .find(|line| !line.is_empty())
+            .unwrap_or("")
+            .to_string()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_strip_comments_with_leading_comment() {
+        let content = "# This is a comment\n20.16.0";
+        assert_eq!(Nvmrc::strip_comments(content), "20.16.0");
+    }
+
+    #[test]
+    fn test_strip_comments_with_inline_comment() {
+        let content = "20.16.0 # this is Node 20 LTS";
+        assert_eq!(Nvmrc::strip_comments(content), "20.16.0");
+    }
+
+    #[test]
+    fn test_strip_comments_with_multiple_comments() {
+        let content = "# First comment\n# Second comment\n18.0.0\n# Trailing comment";
+        assert_eq!(Nvmrc::strip_comments(content), "18.0.0");
+    }
+
+    #[test]
+    fn test_strip_comments_with_lts_alias() {
+        let content = "lts/iron\n\n# (maps to Node v20 LTS)";
+        assert_eq!(Nvmrc::strip_comments(content), "lts/iron");
+    }
+
+    #[test]
+    fn test_strip_comments_with_empty_lines() {
+        let content = "\n\n# comment\n\nv21.x.x\n\n# another comment";
+        assert_eq!(Nvmrc::strip_comments(content), "v21.x.x");
+    }
+
+    #[test]
+    fn test_strip_comments_with_whitespace() {
+        let content = "  # comment with spaces  \n  20.16.0  ";
+        assert_eq!(Nvmrc::strip_comments(content), "20.16.0");
+    }
+
+    #[test]
+    fn test_strip_comments_only_comments() {
+        let content = "# comment 1\n# comment 2\n# comment 3";
+        assert_eq!(Nvmrc::strip_comments(content), "");
+    }
+
+    #[test]
+    fn test_strip_comments_empty_string() {
+        let content = "";
+        assert_eq!(Nvmrc::strip_comments(content), "");
+    }
+
+    #[test]
+    fn test_strip_comments_whitespace_only() {
+        let content = "   \n\n   \n";
+        assert_eq!(Nvmrc::strip_comments(content), "");
+    }
+
+    #[test]
+    fn test_strip_comments_no_comments() {
+        let content = "20.16.0";
+        assert_eq!(Nvmrc::strip_comments(content), "20.16.0");
+    }
+
+    #[test]
+    fn test_strip_comments_multiple_versions_takes_first() {
+        let content = "20.16.0\n18.0.0";
+        assert_eq!(Nvmrc::strip_comments(content), "20.16.0");
+    }
+
+    #[test]
+    fn test_strip_comments_with_v_prefix() {
+        let content = "# Use Node 20\nv20.16.0 # Latest LTS";
+        assert_eq!(Nvmrc::strip_comments(content), "v20.16.0");
+    }
+
+    #[test]
+    fn test_version_parsing() {
+        let nvmrc = Nvmrc::parse("# comment\n20.16.0".to_string()).unwrap();
+        assert!(nvmrc.version().is_some());
+    }
+
+    #[test]
+    fn test_version_parsing_with_inline_comment() {
+        let nvmrc = Nvmrc::parse("20.16.0 # comment".to_string()).unwrap();
+        assert!(nvmrc.version().is_some());
+    }
+
+    #[test]
+    fn test_version_parsing_only_comments() {
+        let nvmrc = Nvmrc::parse("# only comments".to_string()).unwrap();
+        assert!(nvmrc.version().is_none());
+    }
+}
diff --git a/src/version_file_format.rs b/src/version_file_format.rs
new file mode 100644
index 000000000..d9933fbb7
--- /dev/null
+++ b/src/version_file_format.rs
@@ -0,0 +1,60 @@
+use std::path::Path;
+
+#[derive(Debug, PartialEq)]
+pub enum VersionFileFormat {
+    Nvmrc,
+    PackageJson,
+    Other,
+}
+
+impl VersionFileFormat {
+    pub fn infer_from_path(path: &Path) -> Self {
+        match path.file_name().and_then(|name| name.to_str()) {
+            Some(".nvmrc") => Self::Nvmrc,
+            Some("package.json") => Self::PackageJson,
+            _ => Self::Other,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::path::PathBuf;
+
+    #[test]
+    fn test_infer_nvmrc() {
+        let path = PathBuf::from("/some/path/.nvmrc");
+        assert_eq!(
+            VersionFileFormat::infer_from_path(&path),
+            VersionFileFormat::Nvmrc
+        );
+    }
+
+    #[test]
+    fn test_infer_package_json() {
+        let path = PathBuf::from("/some/path/package.json");
+        assert_eq!(
+            VersionFileFormat::infer_from_path(&path),
+            VersionFileFormat::PackageJson
+        );
+    }
+
+    #[test]
+    fn test_infer_node_version() {
+        let path = PathBuf::from("/some/path/.node-version");
+        assert_eq!(
+            VersionFileFormat::infer_from_path(&path),
+            VersionFileFormat::Other
+        );
+    }
+
+    #[test]
+    fn test_infer_unknown() {
+        let path = PathBuf::from("/some/path/unknown.txt");
+        assert_eq!(
+            VersionFileFormat::infer_from_path(&path),
+            VersionFileFormat::Other
+        );
+    }
+}
diff --git a/src/version_files.rs b/src/version_files.rs
index 59c54adb0..e064f0ce3 100644
--- a/src/version_files.rs
+++ b/src/version_files.rs
@@ -1,7 +1,9 @@
 use crate::config::FnmConfig;
 use crate::default_version;
+use crate::nvmrc::Nvmrc;
 use crate::package_json::PackageJson;
 use crate::user_version::UserVersion;
+use crate::version_file_format::VersionFileFormat;
 use crate::version_file_strategy::VersionFileStrategy;
 use encoding_rs_io::DecodeReaderBytes;
 use log::info;
@@ -67,10 +69,7 @@ pub fn get_user_version_for_file(
     path: impl AsRef<Path>,
     config: &FnmConfig,
 ) -> Option<UserVersion> {
-    let is_pkg_json = match path.as_ref().file_name() {
-        Some(name) => name == "package.json",
-        None => false,
-    };
+    let format = VersionFileFormat::infer_from_path(path.as_ref());
     let file = std::fs::File::open(path).ok()?;
     let file = {
         let mut reader = DecodeReaderBytes::new(file);
@@ -78,17 +77,16 @@ pub fn get_user_version_for_file(
         reader.read_to_string(&mut version).map(|_| version)
     };
 
-    match (file, is_pkg_json, config.resolve_engines()) {
-        (_, true, false) => None,
-        (Err(err), _, _) => {
+    match (file, format) {
+        (Err(err), _) => {
             info!("Can't read file: {}", err);
             None
         }
-        (Ok(version), false, _) => {
-            info!("Found string {:?} in version file", version);
-            UserVersion::from_str(version.trim()).ok()
-        }
-        (Ok(pkg_json), true, true) => {
+        (Ok(pkg_json), VersionFileFormat::PackageJson) => {
+            if !config.resolve_engines() {
+                return None;
+            }
+
             let pkg_json = serde_json::from_str::<PackageJson>(&pkg_json).ok();
             let range: Option<node_semver::Range> =
                 pkg_json.as_ref().and_then(PackageJson::node_range).cloned();
@@ -101,5 +99,19 @@ pub fn get_user_version_for_file(
                 None
             }
         }
+        (Ok(nvmrc), VersionFileFormat::Nvmrc) => {
+            let version = Nvmrc::parse(nvmrc).and_then(Nvmrc::version);
+
+            if let Some(version) = &version {
+                info!("Parsed {:?} from .nvmrc", version);
+            } else {
+                info!("Could not parse .nvmrc");
+            }
+            version
+        }
+        (Ok(content), VersionFileFormat::Other) => {
+            info!("Found string {:?} in version file", content);
+            UserVersion::from_str(content.trim()).ok()
+        }
     }
 }

From 0b19a85d1e34796f872023b75fbbc87114e0533a Mon Sep 17 00:00:00 2001
From: Dan Bjorge <dan.bjorge@deque.com>
Date: Wed, 14 Jan 2026 16:16:42 -0800
Subject: [PATCH 2/2] refactor: clean up syntax of nvmrc parsing logs

---
 src/version_files.rs | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/src/version_files.rs b/src/version_files.rs
index e064f0ce3..331b2f4f9 100644
--- a/src/version_files.rs
+++ b/src/version_files.rs
@@ -101,11 +101,9 @@ pub fn get_user_version_for_file(
         }
         (Ok(nvmrc), VersionFileFormat::Nvmrc) => {
             let version = Nvmrc::parse(nvmrc).and_then(Nvmrc::version);
-
-            if let Some(version) = &version {
-                info!("Parsed {:?} from .nvmrc", version);
-            } else {
-                info!("Could not parse .nvmrc");
+            match &version {
+                Some(v) => info!("Parsed {:?} from .nvmrc", v),
+                None => info!("Could not parse .nvmrc"),
             }
             version
         }