Auto merge of #6980 - Eh2406:varisat, r=alexcrichton

Test the Resolver against the varisat Library

Resolution can be reduced to the SAT problem. So this is an alternative implementation of the resolver that uses a SAT library for the hard work. This is intended to be easy to read, as compared to the real resolver, and run as part of the test sweet to make sure the real resolver works as expected. Part of #6120.

Some notes on performance:
The initial version did not support public & private deps:
~64 loc, `O(nln(n))` vars, `O(nln(n) + n*d)` clauses, 0.5x slower on `prop_passes_validation`
The final version:
~163 loc, `O(dn^2`) vars, `O(dn^3)`  clauses, 1.5x slower on `prop_passes_validation`

That comparison makes me feel better about spending months trying to get public & private deps to be fast enough for stabilization.

Cargo.toml

@@ -103,6 +103,7 @@ features = [
 [dev-dependencies]
 bufstream = "0.1"
 proptest = "0.9.1"
+varisat = "0.2.1"
 
 [[bin]]
 name = "cargo"

tests/testsuite/resolve.rs

@@ -9,7 +9,7 @@ use crate::support::registry::Package;
 use crate::support::resolver::{
     assert_contains, assert_same, dep, dep_kind, dep_loc, dep_req, dep_req_kind, loc_names, names,
     pkg, pkg_dep, pkg_id, pkg_loc, registry, registry_strategy, remove_dep, resolve,
-    resolve_and_validated, resolve_with_config, PrettyPrintRegistry, ToDep, ToPkgId,
+    resolve_and_validated, resolve_with_config, PrettyPrintRegistry, SatResolve, ToDep, ToPkgId,
 };
 
 use proptest::prelude::*;
@@ -41,6 +41,7 @@ proptest! {
         PrettyPrintRegistry(input) in registry_strategy(50, 20, 60)
     )  {
         let reg = registry(input.clone());
+        let mut sat_resolve = SatResolve::new(&reg);
         // there is only a small chance that any one
         // crate will be interesting.
         // So we try some of the most complicated.
@@ -49,6 +50,7 @@ proptest! {
                 pkg_id("root"),
                 vec![dep_req(&this.name(), &format!("={}", this.version()))],
                 &reg,
+                Some(&mut sat_resolve),
             );
         }
     }
@@ -236,6 +238,18 @@ proptest! {
     }
 }
 
+#[test]
+fn pub_fail() {
+    let input = vec![
+        pkg!(("a", "0.0.4")),
+        pkg!(("a", "0.0.5")),
+        pkg!(("e", "0.0.6") => [dep_req_kind("a", "<= 0.0.4", Kind::Normal, true),]),
+        pkg!(("kB", "0.0.3") => [dep_req("a", ">= 0.0.5"),dep("e"),]),
+    ];
+    let reg = registry(input.clone());
+    assert!(resolve_and_validated(pkg_id("root"), vec![dep("kB")], &reg, None).is_err());
+}
+
 #[test]
 fn basic_public_dependency() {
     let reg = registry(vec![
@@ -245,7 +259,7 @@ fn basic_public_dependency() {
         pkg!("C" => [dep("A"), dep("B")]),
     ]);
 
-    let res = resolve_and_validated(pkg_id("root"), vec![dep("C")], &reg).unwrap();
+    let res = resolve_and_validated(pkg_id("root"), vec![dep("C")], &reg, None).unwrap();
     assert_same(
         &res,
         &names(&[
@@ -281,7 +295,7 @@ fn public_dependency_filling_in() {
         pkg!("d" => [dep("c"), dep("a"), dep("b")]),
     ]);
 
-    let res = resolve_and_validated(pkg_id("root"), vec![dep("d")], &reg).unwrap();
+    let res = resolve_and_validated(pkg_id("root"), vec![dep("d")], &reg, None).unwrap();
     assert_same(
         &res,
         &names(&[
@@ -316,7 +330,7 @@ fn public_dependency_filling_in_and_update() {
         pkg!("C" => [dep("A"),dep("B")]),
         pkg!("D" => [dep("B"),dep("C")]),
     ]);
-    let res = resolve_and_validated(pkg_id("root"), vec![dep("D")], &reg).unwrap();
+    let res = resolve_and_validated(pkg_id("root"), vec![dep("D")], &reg, None).unwrap();
     assert_same(
         &res,
         &names(&[
@@ -1407,7 +1421,7 @@ fn conflict_store_bug() {
     ];
 
     let reg = registry(input);
-    let _ = resolve_and_validated(pkg_id("root"), vec![dep("j")], &reg);
+    let _ = resolve_and_validated(pkg_id("root"), vec![dep("j")], &reg, None);
 }
 
 #[test]
@@ -1435,5 +1449,5 @@ fn conflict_store_more_then_one_match() {
         ]),
     ];
     let reg = registry(input);
-    let _ = resolve_and_validated(pkg_id("root"), vec![dep("nA")], &reg);
+    let _ = resolve_and_validated(pkg_id("root"), vec![dep("nA")], &reg, None);
 }