perf(builtin,test): assert_true/assert_false/fail accept StringView msg

`fail`, `assert_true`, `assert_false`, and `@test.fail` all only ever
read their `msg` argument — it's either formatted into a `Failure` error
string via `"\{loc} FAILED: \{msg}"` or substituted as-is in an
interpolation. No reason to require ownership.

Expand the `msg` parameter of each to `StringView`. Every existing
caller keeps compiling — `String` values coerce to `StringView` at
argument passing, as do literal strings.

Continues the view-safe expansion theme (#3459, #3460, #3461, #3462).

Author: bobzhang

builtin/assert.mbt

@@ -122,9 +122,9 @@ pub fn[T : Eq + Show] assert_not_eq(
 /// ```
 #callsite(autofill(loc))
 #coverage.skip
-pub fn assert_true(x : Bool, msg? : String, loc~ : SourceLoc) -> Unit raise {
+pub fn assert_true(x : Bool, msg? : StringView, loc~ : SourceLoc) -> Unit raise {
   if !x {
-    let fail_msg = match msg {
+    let fail_msg : StringView = match msg {
       Some(msg) => msg
       None => "`\{x}` is not true"
     }
@@ -155,9 +155,13 @@ pub fn assert_true(x : Bool, msg? : String, loc~ : SourceLoc) -> Unit raise {
 /// ```
 #callsite(autofill(loc))
 #coverage.skip
-pub fn assert_false(x : Bool, msg? : String, loc~ : SourceLoc) -> Unit raise {
+pub fn assert_false(
+  x : Bool,
+  msg? : StringView,
+  loc~ : SourceLoc,
+) -> Unit raise {
   if x {
-    let fail_msg = match msg {
+    let fail_msg : StringView = match msg {
       Some(msg) => msg
       None => "`\{x}` is not false"
     }

builtin/failure.mbt

@@ -54,6 +54,6 @@ pub(all) suberror Failure {
 /// Throws an error of type `Failure` with a message that includes both the
 /// source location and the provided error message.
 #callsite(autofill(loc))
-pub fn[T] fail(msg : String, loc~ : SourceLoc) -> T raise Failure {
+pub fn[T] fail(msg : StringView, loc~ : SourceLoc) -> T raise Failure {
   raise Failure("\{loc} FAILED: \{msg}")
 }

builtin/pkg.generated.mbti

@@ -9,19 +9,19 @@ pub fn[T] abort(String) -> T
 pub fn[T : Eq + Show] assert_eq(T, T, msg? : String, loc~ : SourceLoc) -> Unit raise
 
 #callsite(autofill(loc))
-pub fn assert_false(Bool, msg? : String, loc~ : SourceLoc) -> Unit raise
+pub fn assert_false(Bool, msg? : StringView, loc~ : SourceLoc) -> Unit raise
 
 #deprecated
 #callsite(autofill(loc))
 pub fn[T : Eq + Show] assert_not_eq(T, T, msg? : String, loc~ : SourceLoc) -> Unit raise
 
 #callsite(autofill(loc))
-pub fn assert_true(Bool, msg? : String, loc~ : SourceLoc) -> Unit raise
+pub fn assert_true(Bool, msg? : StringView, loc~ : SourceLoc) -> Unit raise
 
 pub fn debug_assert(() -> Bool) -> Unit
 
 #callsite(autofill(loc))
-pub fn[T] fail(String, loc~ : SourceLoc) -> T raise Failure
+pub fn[T] fail(StringView, loc~ : SourceLoc) -> T raise Failure
 
 pub fn[T] ignore(T) -> Unit
 

prelude/pkg.generated.mbti

@@ -18,13 +18,13 @@ pub fn[T] abort(String) -> T
 pub fn[T : @builtin.Eq + @builtin.Show] assert_eq(T, T, msg? : String, loc~ : @builtin.SourceLoc) -> Unit raise
 
 #callsite(autofill(loc))
-pub fn assert_false(Bool, msg? : String, loc~ : @builtin.SourceLoc) -> Unit raise
+pub fn assert_false(Bool, msg? : StringView, loc~ : @builtin.SourceLoc) -> Unit raise
 
 #callsite(autofill(loc))
 pub fn[T : @builtin.Eq + @builtin.Show] assert_not_eq(T, T, msg? : String, loc~ : @builtin.SourceLoc) -> Unit raise
 
 #callsite(autofill(loc))
-pub fn assert_true(Bool, msg? : String, loc~ : @builtin.SourceLoc) -> Unit raise
+pub fn assert_true(Bool, msg? : StringView, loc~ : @builtin.SourceLoc) -> Unit raise
 
 pub fn[T : @debug.Debug] debug(T) -> Unit
 
@@ -38,7 +38,7 @@ pub fn debug_inspect(&@debug.Debug, content? : String, loc~ : @builtin.SourceLoc
 pub fn[T : @debug.Debug] dump(T, name? : String, loc~ : @builtin.SourceLoc) -> T
 
 #callsite(autofill(loc))
-pub fn[T] fail(String, loc~ : @builtin.SourceLoc) -> T raise @builtin.Failure
+pub fn[T] fail(StringView, loc~ : @builtin.SourceLoc) -> T raise @builtin.Failure
 
 pub fn[T] ignore(T) -> Unit
 

test/pkg.generated.mbti

@@ -19,7 +19,7 @@ pub fn[T : @debug.Debug] assert_not_same_object(T, T, loc~ : SourceLoc) -> Unit
 pub fn[T : @debug.Debug] assert_same_object(T, T, loc~ : SourceLoc) -> Unit raise
 
 #callsite(autofill(loc))
-pub fn[T] fail(String, loc~ : SourceLoc) -> T raise
+pub fn[T] fail(StringView, loc~ : SourceLoc) -> T raise
 
 #alias(is_not, deprecated)
 #deprecated

test/test.mbt

@@ -154,7 +154,7 @@ pub fn[T : Debug] assert_not_same_object(
 ///  
 /// Produces an error message similar to @builtin.fail.
 #callsite(autofill(loc))
-pub fn[T] fail(msg : String, loc~ : SourceLoc) -> T raise {
+pub fn[T] fail(msg : StringView, loc~ : SourceLoc) -> T raise {
   @builtin.fail(msg, loc~)
 }