add platform tests and implementation

That way, the platform can be used to perform actual merges.
This will also be a good chance to try the API.

Author: Byron

gix-merge/src/blob/builtin_driver/text/function.rs

@@ -3,13 +3,12 @@ use crate::blob::builtin_driver::text::utils::{
     hunks_differ_in_diff3, take_intersecting, tokens, write_ancestor, write_conflict_marker, write_hunks,
     zealously_contract_hunks, CollectHunks, Hunk, Side,
 };
-use crate::blob::builtin_driver::text::{ConflictStyle, Options, ResolveWith};
+use crate::blob::builtin_driver::text::{ConflictStyle, Labels, Options, ResolveWith};
 use crate::blob::Resolution;
-use bstr::BStr;
 
 /// Merge `current` and `other` with `ancestor` as base according to `opts`.
 ///
-/// Use `current_label`, `other_label` and `ancestor_label` to annotate conflict sections.
+/// Use `labels` to annotate conflict sections.
 ///
 /// `input` is for reusing memory for lists of tokens, but note that it grows indefinitely
 /// while tokens for `current`, `ancestor` and `other` are added.
@@ -23,12 +22,14 @@ use bstr::BStr;
 pub fn merge<'a>(
     out: &mut Vec<u8>,
     input: &mut imara_diff::intern::InternedInput<&'a [u8]>,
+    Labels {
+        ancestor: ancestor_label,
+        current: current_label,
+        other: other_label,
+    }: Labels<'_>,
     current: &'a [u8],
-    current_label: Option<&BStr>,
     ancestor: &'a [u8],
-    ancestor_label: Option<&BStr>,
     other: &'a [u8],
-    other_label: Option<&BStr>,
     opts: Options,
 ) -> Resolution {
     out.clear();

gix-merge/src/blob/builtin_driver/text/mod.rs

@@ -1,3 +1,5 @@
+use bstr::BStr;
+
 /// The way the built-in [text driver](crate::blob::BuiltinDriver::Text) will express
 /// merge conflicts in the resulting file.
 #[derive(Default, Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
@@ -48,6 +50,16 @@ pub enum ConflictStyle {
     ZealousDiff3,
 }
 
+/// The set of labels to annotate conflict markers with.
+///
+/// That way it becomes clearer where the content of conflicts are originating from.
+#[derive(Default, Copy, Clone, Debug, Eq, PartialEq)]
+pub struct Labels<'a> {
+    pub ancestor: Option<&'a BStr>,
+    pub current: Option<&'a BStr>,
+    pub other: Option<&'a BStr>,
+}
+
 /// Options for the builtin [text driver](crate::blob::BuiltinDriver::Text).
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub struct Options {

gix-merge/src/blob/mod.rs

@@ -1,6 +1,7 @@
 // TODO: remove this - only needed while &mut Vec<u8> isn't used.
 #![allow(clippy::ptr_arg)]
 
+use crate::blob::platform::{DriverChoice, ResourceRef};
 use bstr::BString;
 use std::path::PathBuf;
 
@@ -157,3 +158,24 @@ pub struct Platform {
     /// The way we convert resources into mergeable states.
     filter_mode: pipeline::Mode,
 }
+
+/// The product of a [`prepare_merge()`](Platform::prepare_merge()) call to finally
+/// perform the merge and retrieve the merge results.
+#[derive(Copy, Clone)]
+pub struct PlatformRef<'parent> {
+    /// The platform that hosts the resources, used to access drivers.
+    pub(super) parent: &'parent Platform,
+    /// The current or our side of the merge operation.
+    pub current: ResourceRef<'parent>,
+    /// The ancestor or base of the merge operation.
+    pub ancestor: ResourceRef<'parent>,
+    /// The other or their side of the merge operation.
+    pub other: ResourceRef<'parent>,
+    /// Which driver to use according to the resource's configuration,
+    /// using the path of `current` to read git-attributes.
+    pub driver: DriverChoice,
+    /// Possibly processed options for use when performing the actual merge.
+    ///
+    /// They may be inspected before the merge, or altered at will.
+    pub options: platform::merge::Options,
+}