Add `Harness::debug_open_snapshot` helper (#7590)

Adds a helper to quickly see whats going on in a kittest test.

Not all test have snapshots, but when debugging tests it might still be
useful to see whats actually going on, so this adds a helper fn that
renders a snapshot image to a temporary file and opens it with the
default image viewer:



https://github.com/user-attachments/assets/08785850-0a12-4572-b9b5-cea36951081c

Cargo.lock

@@ -1422,7 +1422,9 @@ dependencies = [
  "egui_extras",
  "image",
  "kittest",
+ "open",
  "pollster",
+ "tempfile",
  "wgpu",
 ]
 
@@ -2318,6 +2320,15 @@ dependencies = [
  "hashbrown 0.15.2",
 ]
 
+[[package]]
+name = "is-docker"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "928bae27f42bc99b60d9ac7334e3a21d10ad8f1835a4e12ec3ec0464765ed1b3"
+dependencies = [
+ "once_cell",
+]
+
 [[package]]
 name = "is-terminal"
 version = "0.4.13"
@@ -2329,6 +2340,16 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
+[[package]]
+name = "is-wsl"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "173609498df190136aa7dea1a91db051746d339e18476eed5ca40521f02d7aa5"
+dependencies = [
+ "is-docker",
+ "once_cell",
+]
+
 [[package]]
 name = "itertools"
 version = "0.10.5"
@@ -3065,6 +3086,17 @@ version = "11.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b410bbe7e14ab526a0e86877eb47c6996a2bd7746f027ba551028c925390e4e9"
 
+[[package]]
+name = "open"
+version = "5.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e2483562e62ea94312f3576a7aca397306df7990b8d89033e18766744377ef95"
+dependencies = [
+ "is-wsl",
+ "libc",
+ "pathdiff",
+]
+
 [[package]]
 name = "option-ext"
 version = "0.2.0"
@@ -3143,6 +3175,12 @@ version = "1.0.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "57c0d7b74b563b49d38dae00a0c37d4d6de9b432382b2892f0574ddcae73fd0a"
 
+[[package]]
+name = "pathdiff"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "df94ce210e5bc13cb6651479fa48d14f601d9858cfe0467f43ae157023b938d3"
+
 [[package]]
 name = "percent-encoding"
 version = "2.3.1"
@@ -4064,15 +4102,15 @@ dependencies = [
 
 [[package]]
 name = "tempfile"
-version = "3.13.0"
+version = "3.23.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f0f2c9fc62d0beef6951ccffd757e241266a2c833136efbe35af6cd2567dca5b"
+checksum = "2d31c77bdf42a745371d260a26ca7163f1e0924b64afa0b688e61b5a9fa02f16"
 dependencies = [
- "cfg-if",
  "fastrand",
+ "getrandom 0.3.1",
  "once_cell",
- "rustix 0.38.38",
+ "rustix 1.0.8",
- "windows-sys 0.59.0",
+ "windows-sys 0.60.2",
 ]
 
 [[package]]

Cargo.toml

@@ -95,6 +95,7 @@ objc2 = "0.5.1"
 objc2-app-kit = { version = "0.2.0", default-features = false }
 objc2-foundation = { version = "0.2.0", default-features = false }
 objc2-ui-kit = { version = "0.2.0", default-features = false }
+open = "5"
 parking_lot = "0.12"
 percent-encoding = "2.1"
 pollster = "0.4"
@@ -107,6 +108,7 @@ serde = { version = "1", features = ["derive"] }
 similar-asserts = "1.4.2"
 smallvec = "1"
 static_assertions = "1.1.0"
+tempfile = "3"
 thiserror = "1.0.37"
 type-map = "0.5.0"
 unicode-segmentation = "1.12.0"
@@ -114,7 +116,7 @@ wasm-bindgen = "0.2"
 wasm-bindgen-futures = "0.4"
 web-sys = "0.3.73"
 web-time = "1.1.0" # Timekeeping for native and web
-wgpu = { version = "27.0.0", default-features = false }
+wgpu = { version = "27.0.0", default-features = false, features = ["std"] }
 windows-sys = "0.60"
 winit = { version = "0.30.12", default-features = false }
 

clippy.toml

@@ -39,7 +39,7 @@ disallowed-methods = [
     # but we cannot disable them all here (because of e.g. https://github.com/rust-lang/rust-clippy/issues/10406)
     # so we do that in `clipppy_wasm.toml` instead.
 
-    { path = "std::env::temp_dir", readon = "Use the tempdir crate instead" },
+    { path = "std::env::temp_dir", readon = "Use the tempfile crate instead" },
     { path = "std::panic::catch_unwind", reason = "We compile with `panic = abort" },
     { path = "std::thread::spawn", readon = "Use `std::thread::Builder` and name the thread" },
 ]

crates/egui_kittest/Cargo.toml

@@ -33,7 +33,7 @@ wgpu = [
 ]
 
 ## Adds a dify-based image snapshot utility.
-snapshot = ["dep:dify", "dep:image", "image/png"]
+snapshot = ["dep:dify", "dep:image", "dep:open", "dep:tempfile", "image/png"]
 
 ## Allows testing eframe::App
 eframe = ["dep:eframe", "eframe/accesskit"]
@@ -61,6 +61,8 @@ wgpu = { workspace = true, features = [
 
 # snapshot dependencies
 dify = { workspace = true, optional = true }
+open = { workspace = true, optional = true }
+tempfile = { workspace = true, optional = true }
 
 # Enable this when generating docs.
 document-features = { workspace = true, optional = true }

crates/egui_kittest/src/snapshot.rs

@@ -544,7 +544,7 @@ pub fn image_snapshot(current: &image::RgbaImage, name: impl Into<String>) {
     }
 }
 
-#[cfg(feature = "wgpu")]
+#[cfg(any(feature = "wgpu", feature = "snapshot"))]
 impl<State> Harness<'_, State> {
     /// Render an image using the setup [`crate::TestRenderer`] and compare it to the snapshot
     /// with custom options.
@@ -635,6 +635,49 @@ impl<State> Harness<'_, State> {
             }
         }
     }
+
+    /// Render a snapshot, save it to a temp file and open it in the default image viewer.
+    ///
+    /// This method is marked as deprecated to trigger errors in CI (so that it's not accidentally
+    /// committed).
+    #[deprecated = "Only for debugging, don't commit this."]
+    pub fn debug_open_snapshot(&mut self) {
+        let image = self
+            .render()
+            .map_err(|err| SnapshotError::RenderError { err })
+            .unwrap();
+        let temp_file = tempfile::Builder::new()
+            .disable_cleanup(true) // we keep the file so it's accessible even after the test ends
+            .prefix("kittest-snapshot")
+            .suffix(".png")
+            .tempfile()
+            .expect("Failed to create temp file");
+
+        let path = temp_file.path();
+
+        image
+            .save(temp_file.path())
+            .map_err(|err| SnapshotError::WriteSnapshot {
+                err,
+                path: path.to_path_buf(),
+            })
+            .unwrap();
+
+        #[expect(clippy::print_stdout)]
+        {
+            println!("Wrote debug snapshot to: {}", path.display());
+        }
+        let result = open::that(path);
+        if let Err(err) = result {
+            #[expect(clippy::print_stderr)]
+            {
+                eprintln!(
+                    "Failed to open image {} in default image viewer: {err}",
+                    path.display()
+                );
+            }
+        }
+    }
 }
 
 /// Utility to collect snapshot errors and display them at the end of the test.

deny.toml

@@ -48,13 +48,14 @@ skip = [
   { name = "bit-set" },             # wgpu's naga depends on 0.8, syntect's (used by egui_extras) fancy-regex depends on 0.5
   { name = "bit-vec" },             # dependency of bit-set in turn, different between 0.6 and 0.5
   { name = "bitflags" },            # old 1.0 version via glutin, png, spirv, …
+  { name = "core-foundation" },     # version conflict between winit and wgpu ecosystems
+  { name = "core-graphics-types" }, # version conflict between winit and wgpu ecosystems
+  { name = "getrandom" },           # ring / rustls (and thus ehttp) still depend on getrandom 0.2
   { name = "quick-xml" },           # old version via wayland-scanner
   { name = "redox_syscall" },       # old version via winit
   { name = "thiserror" },           # ecosystem is in the process of migrating from 1.x to 2.x
   { name = "thiserror-impl" },      # same as above
   { name = "windows-sys" },         # mostly hopeless to avoid
-  { name = "core-foundation" },     # version conflict between winit and wgpu ecosystems
-  { name = "core-graphics-types" }, # version conflict between winit and wgpu ecosystems
 ]
 skip-tree = [
   { name = "hashbrown" }, # wgpu's naga depends on 0.16, accesskit depends on 0.15