Rust: Implement type inference for 'for' loops on arrays.

Author: geoffw0

rust/ql/lib/codeql/rust/internal/TypeInference.qll

@@ -1180,6 +1180,20 @@ private Type inferIndexExprType(IndexExpr ie, TypePath path) {
   )
 }
 
+pragma[nomagic]
+private Type inferForLoopExprType(AstNode n, TypePath path) {
+  // type of iterable -> type of pattern (loop variable)
+  exists(ForExpr fe, Type iterableType, TypePath iterablePath |
+    n = fe.getPat() and
+    iterableType = inferType(fe.getIterable(), iterablePath) and
+    (
+      iterablePath.isCons(any(ArrayTypeParameter tp), path) and
+      result = iterableType
+      // TODO: iterables (containers, ranges etc)
+    )
+  )
+}
+
 private module MethodCall {
   /** An expression that calls a method. */
   abstract private class MethodCallImpl extends Expr {
@@ -1541,6 +1555,8 @@ private module Cached {
     result = inferAwaitExprType(n, path)
     or
     result = inferIndexExprType(n, path)
+    or
+    result = inferForLoopExprType(n, path)
   }
 }
 

rust/ql/test/library-tests/type-inference/main.rs

@@ -1833,10 +1833,10 @@ mod loops {
         for u in vals2 { } // $ MISSING: type=u:u16
 
         let vals3: [u32; 3] = [1, 2, 3]; // $ MISSING: type=vals3:[u32; 3]
-        for u in vals3 { } // $ MISSING: type=u:u32
+        for u in vals3 { } // $ type=u:u32
 
         let vals4: [u64; 3] = [1; 3]; // $ MISSING: type=vals4:[u64; 3]
-        for u in vals4 { } // $ MISSING: type=u:u64
+        for u in vals4 { } // $ type=u:u64
 
         let mut strings1 = ["foo", "bar", "baz"]; // $ MISSING: type=strings1:[&str; 3]
         for s in &strings1 { } // $ MISSING: type=s:&str

rust/ql/test/library-tests/type-inference/type-inference.expected

@@ -2641,6 +2641,7 @@ inferType
 | main.rs:1835:32:1835:32 | 1 |  | {EXTERNAL LOCATION} | i32 |
 | main.rs:1835:35:1835:35 | 2 |  | {EXTERNAL LOCATION} | i32 |
 | main.rs:1835:38:1835:38 | 3 |  | {EXTERNAL LOCATION} | i32 |
+| main.rs:1836:13:1836:13 | u |  | {EXTERNAL LOCATION} | u32 |
 | main.rs:1836:18:1836:22 | vals3 |  | file://:0:0:0:0 | [] |
 | main.rs:1836:18:1836:22 | vals3 | [T;...] | {EXTERNAL LOCATION} | u32 |
 | main.rs:1838:13:1838:17 | vals4 |  | file://:0:0:0:0 | [] |
@@ -2650,6 +2651,7 @@ inferType
 | main.rs:1838:31:1838:36 | [1; 3] | [T;...] | {EXTERNAL LOCATION} | u64 |
 | main.rs:1838:32:1838:32 | 1 |  | {EXTERNAL LOCATION} | i32 |
 | main.rs:1838:35:1838:35 | 3 |  | {EXTERNAL LOCATION} | i32 |
+| main.rs:1839:13:1839:13 | u |  | {EXTERNAL LOCATION} | u64 |
 | main.rs:1839:18:1839:22 | vals4 |  | file://:0:0:0:0 | [] |
 | main.rs:1839:18:1839:22 | vals4 | [T;...] | {EXTERNAL LOCATION} | u64 |
 | main.rs:1841:29:1841:33 | "foo" |  | {EXTERNAL LOCATION} | str |