Rename dashes in a few test files to underscores (#2170)

This is somewhat https://github.com/carbon-language/carbon-lang/blob/trunk/docs/project/cpp_style_guide.md#file-names, but in general, underscores are more consistent.

explorer/testdata/addr/fail_method_let.carbon

@@ -28,7 +28,7 @@ class Point {
 
 fn Main() -> i32 {
   let p: Point = Point.Origin();
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/addr/fail-method-let.carbon:[[@LINE+1]]: method GetSetX requires its receiver to be an lvalue
+  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/addr/fail_method_let.carbon:[[@LINE+1]]: method GetSetX requires its receiver to be an lvalue
   var x: auto = p.GetSetX(42);
   if (p.x == 42) {
     return x;

explorer/testdata/addr/fail_method_me_misspelled.carbon

@@ -11,7 +11,7 @@
 package ExplorerTest api;
 
 class C {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/addr/fail-method-me-misspelled.carbon:[[@LINE+1]]: illegal binding pattern in implicit parameter list
+  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/addr/fail_method_me_misspelled.carbon:[[@LINE+1]]: illegal binding pattern in implicit parameter list
   fn F[addr mew: Self*]() {}
 }
 

explorer/testdata/addr/fail_method_me_type.carbon

@@ -32,7 +32,7 @@ class Point {
 
 fn Main() -> i32 {
   var p: Point = Point.Origin();
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/addr/fail-method-me-type.carbon:[[@LINE+1]]: type error in method access, receiver type: 'class Point' is not implicitly convertible to 'class Shape'
+  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/addr/fail_method_me_type.carbon:[[@LINE+1]]: type error in method access, receiver type: 'class Point' is not implicitly convertible to 'class Shape'
   var x: auto = p.GetSetX(42);
   if (p.x == 42) {
     return x;

explorer/testdata/mixin/fail_circular_mixing.carbon

@@ -13,7 +13,7 @@ __mixin M1 {
   fn F1[me: Self](x: Self) -> Self{
      return x;
   }
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail-circular-mixing.carbon:[[@LINE+1]]: 'M3' has not been declared yet
+  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_circular_mixing.carbon:[[@LINE+1]]: 'M3' has not been declared yet
   __mix M3;
 }
 

explorer/testdata/mixin/fail_field_member_name_clash.carbon

@@ -19,7 +19,7 @@ __mixin M {
 class C {
   let F: i32 = 0;
   __mix M;
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail-field-member-name-clash.carbon:[[@LINE+1]]: Member named F (declared at {{.*}}/explorer/testdata/mixin/fail-field-member-name-clash.carbon:16) cannot be mixed into C because it clashes with an existing member with the same name (declared at {{.*}}/explorer/testdata/mixin/fail-field-member-name-clash.carbon:20)
+// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_field_member_name_clash.carbon:[[@LINE+1]]: Member named F (declared at {{.*}}/explorer/testdata/mixin/fail_field_member_name_clash.carbon:16) cannot be mixed into C because it clashes with an existing member with the same name (declared at {{.*}}/explorer/testdata/mixin/fail_field_member_name_clash.carbon:20)
 }
 
 fn Main() -> i32 {

explorer/testdata/mixin/fail_method_member_name_clash.carbon

@@ -21,7 +21,7 @@ class C {
      return x;
   }
   __mix M;
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail-method-member-name-clash.carbon:[[@LINE+1]]: Member named F (declared at {{.*}}/explorer/testdata/mixin/fail-method-member-name-clash.carbon:16) cannot be mixed into C because it clashes with an existing member with the same name (declared at {{.*}}/explorer/testdata/mixin/fail-method-member-name-clash.carbon:22)
+// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_method_member_name_clash.carbon:[[@LINE+1]]: Member named F (declared at {{.*}}/explorer/testdata/mixin/fail_method_member_name_clash.carbon:16) cannot be mixed into C because it clashes with an existing member with the same name (declared at {{.*}}/explorer/testdata/mixin/fail_method_member_name_clash.carbon:22)
 }
 
 fn Main() -> i32 {

explorer/testdata/mixin/fail_mix_as_type_expr.carbon

@@ -13,7 +13,7 @@ package ExplorerTest api;
 __mixin Operations {}
 
 fn Main() -> i32 {
-   // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail-mix-as-type-expr.carbon:[[@LINE+1]]: Expected a type, but got mixin Operations
+   // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_mix_as_type_expr.carbon:[[@LINE+1]]: Expected a type, but got mixin Operations
    var a: Operations;
    return 0;
 }

explorer/testdata/mixin/fail_mix_diamond_clash.carbon

@@ -30,7 +30,7 @@ __mixin M3 {
 class C {
   __mix M2;
   __mix M3;
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail-mix-diamond-clash.carbon:[[@LINE+1]]: Member named F1 (declared at {{.*}}/explorer/testdata/mixin/fail-mix-diamond-clash.carbon:15) is being mixed multiple times into C
+// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_mix_diamond_clash.carbon:[[@LINE+1]]: Member named F1 (declared at {{.*}}/explorer/testdata/mixin/fail_mix_diamond_clash.carbon:15) is being mixed multiple times into C
 }
 
 fn Main() -> i32 {

explorer/testdata/mixin/fail_mix_in_global.carbon

@@ -16,7 +16,7 @@ __mixin Operations {
   }
 }
 
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail-mix-in-global.carbon:[[@LINE+1]]: syntax error, unexpected MIX, expecting END_OF_FILE
+// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_mix_in_global.carbon:[[@LINE+1]]: syntax error, unexpected MIX, expecting END_OF_FILE
 __mix Operations;
 
 class Point {

explorer/testdata/mixin/fail_mix_in_impl.carbon

@@ -21,7 +21,7 @@ interface A {
 }
 
 external impl i32 as A {
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail-mix-in-impl.carbon:[[@LINE+1]]: syntax error, unexpected MIX, expecting ALIAS or FN or RIGHT_CURLY_BRACE
+  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_mix_in_impl.carbon:[[@LINE+1]]: syntax error, unexpected MIX, expecting ALIAS or FN or RIGHT_CURLY_BRACE
   __mix Operations;
   fn F() {}
 }

explorer/testdata/mixin/fail_mix_members_clash.carbon

@@ -23,7 +23,7 @@ __mixin M2 {
 class C {
   __mix M1;
   __mix M2;
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail-mix-members-clash.carbon:[[@LINE+1]]: Member named F1 (declared at {{.*}}/explorer/testdata/mixin/fail-mix-members-clash.carbon:20) cannot be mixed into C because it clashes with an existing member with the same name (declared at {{.*}}/explorer/testdata/mixin/fail-mix-members-clash.carbon:15)
+// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_mix_members_clash.carbon:[[@LINE+1]]: Member named F1 (declared at {{.*}}/explorer/testdata/mixin/fail_mix_members_clash.carbon:20) cannot be mixed into C because it clashes with an existing member with the same name (declared at {{.*}}/explorer/testdata/mixin/fail_mix_members_clash.carbon:15)
 }
 
 fn Main() -> i32 {

explorer/testdata/mixin/fail_recursive_mixing.carbon

@@ -14,7 +14,7 @@ __mixin M1 {
      return x;
   }
   __mix M1;
-// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail-recursive-mixing.carbon:[[@LINE+1]]: Member named F1 (declared at {{.*}}/explorer/testdata/mixin/fail-recursive-mixing.carbon:15) is being mixed multiple times into M1
+// CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_recursive_mixing.carbon:[[@LINE+1]]: Member named F1 (declared at {{.*}}/explorer/testdata/mixin/fail_recursive_mixing.carbon:15) is being mixed multiple times into M1
 }
 
 class C {

explorer/testdata/mixin/fail_self_substitution.carbon

@@ -38,7 +38,7 @@ class Complex {
 fn Main() -> i32 {
   var p: Point = Point.Origin();
   var c: Complex = {.r = 42, .i = 1};
-  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail-self-substitution.carbon:[[@LINE+1]]: type error in call: 'class Complex' is not implicitly convertible to 'class Point'
+  // CHECK: COMPILATION ERROR: {{.*}}/explorer/testdata/mixin/fail_self_substitution.carbon:[[@LINE+1]]: type error in call: 'class Complex' is not implicitly convertible to 'class Point'
   var p1: Point = p.F(c);
 
   return p1.x - 42;