Support target-spec json file extension in case-insensitive form

src/cargo/core/compiler/compile_kind.rs

@@ -7,6 +7,7 @@ use crate::util::{try_canonicalize, GlobalContext, StableHasher};
 use anyhow::Context as _;
 use serde::Serialize;
 use std::collections::BTreeSet;
+use std::ffi::OsStr;
 use std::fs;
 use std::hash::{Hash, Hasher};
 use std::path::Path;
@@ -131,7 +132,7 @@ impl CompileTarget {
         if name.is_empty() {
             anyhow::bail!("target was empty");
         }
-        if !name.ends_with(".json") {
+        if !name.has_json_ext_ignore_case() {
             return Ok(CompileTarget { name: name.into() });
         }
 
@@ -170,7 +171,7 @@ impl CompileTarget {
         // name without ".json") as a short name for this target. Note that the
         // `unwrap()` here should never trigger since we have a nonempty name
         // and it starts as utf-8 so it's always utf-8
-        if self.name.ends_with(".json") {
+        if self.has_json_ext_ignore_case() {
             Path::new(&self.name).file_stem().unwrap().to_str().unwrap()
         } else {
             &self.name
@@ -181,8 +182,7 @@ impl CompileTarget {
     pub fn fingerprint_hash(&self) -> u64 {
         let mut hasher = StableHasher::new();
         match self
-            .name
-            .ends_with(".json")
+            .has_json_ext_ignore_case()
             .then(|| fs::read_to_string(self.name))
         {
             Some(Ok(contents)) => {
@@ -198,3 +198,55 @@ impl CompileTarget {
         hasher.finish()
     }
 }
+
+pub trait HasExtIgnoreCase {
+    /// Checks if the `self` ends with `ext` __case-insensitive__.
+    /// The `ext` should not have leading dot.
+    ///
+    /// Does not check if the path exists.
+    ///
+    /// Use it only for user's input like target names,
+    /// but not in algorithms like filesystem traversal because on case-sensitive fs it may lead logical errors
+    /// if you'll have met two files "a.foo" and "a.FOO", for example.
+    fn has_ext_ignore_case<Ext: AsRef<OsStr>>(&self, ext: Ext) -> bool;
+
+    /// Checks if the `self` ends with ".json" (case-insensitive).
+    ///
+    /// See [`has_ext_ignore_case`][HasExtIgnoreCase::has_ext_ignore_case],
+    /// used as default implementation.
+    #[inline]
+    fn has_json_ext_ignore_case(&self) -> bool {
+        self.has_ext_ignore_case("json")
+    }
+}
+
+impl<T: AsRef<OsStr>> HasExtIgnoreCase for T {
+    fn has_ext_ignore_case<Ext: AsRef<OsStr>>(&self, ext: Ext) -> bool {
+        Path::new(self)
+            .extension()
+            .is_some_and(|s| s.eq_ignore_ascii_case(ext))
+    }
+}
+
+impl HasExtIgnoreCase for CompileTarget {
+    /// Checks if the name of `self` ends with `ext` __case-insensitive__.
+    /// The `ext` should not have leading dot.
+    ///
+    /// See [`has_ext_ignore_case`][HasExtIgnoreCase::has_ext_ignore_case],
+    fn has_ext_ignore_case<Ext: AsRef<OsStr>>(&self, ext: Ext) -> bool {
+        self.name.has_ext_ignore_case(ext)
+    }
+}
+
+impl HasExtIgnoreCase for CompileKind {
+    /// Checks if the `self`'s target name ends with `ext` __case-insensitive__.
+    /// The `ext` should not have leading dot.
+    ///
+    /// See [`has_ext_ignore_case`][HasExtIgnoreCase::has_ext_ignore_case],
+    fn has_ext_ignore_case<Ext: AsRef<OsStr>>(&self, ext: Ext) -> bool {
+        match self {
+            CompileKind::Host => false,
+            CompileKind::Target(target) => target.has_ext_ignore_case(ext),
+        }
+    }
+}

src/cargo/core/compiler/mod.rs

@@ -74,7 +74,7 @@ pub use self::build_context::{
 use self::build_plan::BuildPlan;
 pub use self::build_runner::{BuildRunner, Metadata};
 pub use self::compilation::{Compilation, Doctest, UnitOutput};
-pub use self::compile_kind::{CompileKind, CompileTarget};
+pub use self::compile_kind::{CompileKind, CompileTarget, HasExtIgnoreCase};
 pub use self::crate_type::CrateType;
 pub use self::custom_build::LinkArgTarget;
 pub use self::custom_build::{BuildOutput, BuildScriptOutputs, BuildScripts};

src/cargo/util/context/mod.rs

@@ -68,6 +68,7 @@ use std::time::Instant;
 
 use self::ConfigValue as CV;
 use crate::core::compiler::rustdoc::RustdocExternMap;
+use crate::core::compiler::HasExtIgnoreCase as _;
 use crate::core::global_cache_tracker::{DeferredGlobalLastUse, GlobalCacheTracker};
 use crate::core::shell::Verbosity;
 use crate::core::{features, CliUnstable, Shell, SourceId, Workspace, WorkspaceRootConfig};
@@ -2651,7 +2652,7 @@ impl BuildTargetConfig {
     /// Gets values of `build.target` as a list of strings.
     pub fn values(&self, gctx: &GlobalContext) -> CargoResult<Vec<String>> {
         let map = |s: &String| {
-            if s.ends_with(".json") {
+            if s.has_json_ext_ignore_case() {
                 // Path to a target specification file (in JSON).
                 // <https://doc.rust-lang.org/rustc/targets/custom.html>
                 self.inner