From 2069bb54585f725a7affe56224d3470c814c7712 Mon Sep 17 00:00:00 2001
From: Michael Ferguson <mppf@users.noreply.github.com>
Date: Mon, 11 Jul 2022 09:28:23 -0400
Subject: [PATCH] Add workarounds to get userInsteadOfStandard working

---
Signed-off-by: Michael Ferguson <mppf@users.noreply.github.com>
---
 compiler/parser/parser.cpp                    | 12 ++++++
 .../bradc/userInsteadOfStandard/AutoMath.chpl | 41 +++++++++++++++++++
 .../bradc/userInsteadOfStandard/foo2.chpl     | 22 ++++++++++
 .../bradc/userInsteadOfStandard/foo2.good     |  4 +-
 4 files changed, 77 insertions(+), 2 deletions(-)

diff --git a/compiler/parser/parser.cpp b/compiler/parser/parser.cpp
index b5abc4a3eb79..4e324204e912 100644
--- a/compiler/parser/parser.cpp
+++ b/compiler/parser/parser.cpp
@@ -537,6 +537,18 @@ static void ensureRequiredStandardModulesAreParsed() {
         }
       }
 
+      // Allow automatically-included standard libraries to be overridden
+      // by a user module.
+      // See also test/modules/bradc/userInsteadOfStandard.
+      // TODO: use a better strategy than this workaround in the future,
+      // such as ideas proposed in issue #19313.
+      if (0 == strcmp(modName, "AutoMath") ||
+          0 == strcmp(modName, "Errors") ||
+          0 == strcmp(modName, "ChapelIO") ||
+          0 == strcmp(modName, "Types")) {
+        foundInt = foundInt || foundUsr;
+      }
+
       // If we haven't found the standard version of the module,
       // then we need to parse it
       if (foundInt == false) {
diff --git a/test/modules/bradc/userInsteadOfStandard/AutoMath.chpl b/test/modules/bradc/userInsteadOfStandard/AutoMath.chpl
index c278056adcd0..bbe5c41ae605 100644
--- a/test/modules/bradc/userInsteadOfStandard/AutoMath.chpl
+++ b/test/modules/bradc/userInsteadOfStandard/AutoMath.chpl
@@ -1,3 +1,44 @@
+// these are needed to compile the standard library,
+// since this module is replacing the standard AutoMath.
+
+proc max(a: int, b: int) {
+  if a > b {
+    return a;
+  } else {
+    return b;
+  }
+}
+proc max(param a: int, param b: int) param {
+  if a > b {
+    return a;
+  } else {
+    return b;
+  }
+}
+
+proc min(a: int, b: int) {
+  if a < b {
+    return a;
+  } else {
+    return b;
+  }
+}
+proc min(param a: int, param b: int) param {
+  if a < b {
+    return a;
+  } else {
+    return b;
+  }
+}
+
+proc abs(a: int) {
+  if a < 0 {
+    return -a;
+  } else {
+    return a;
+  }
+}
+
 proc testmath() {
   writeln("In my math!");
 }
diff --git a/test/modules/bradc/userInsteadOfStandard/foo2.chpl b/test/modules/bradc/userInsteadOfStandard/foo2.chpl
index c8cab074c4bd..3bfbe24b413f 100644
--- a/test/modules/bradc/userInsteadOfStandard/foo2.chpl
+++ b/test/modules/bradc/userInsteadOfStandard/foo2.chpl
@@ -1,3 +1,25 @@
+// This test replaces an automatically-included standard library file with
+// a user one because AutoMath.chpl exists as a sibling to this file.
+
+// While this test uses AutoMath, as of this writing, there are 4 automatic
+// standard libraries: AutoMath, Errors, ChapelIO, and Types.
+// A workaround in parser.cpp allows this replacing process for these
+// except for Errors (because it runs into another workaround in the parser).
+// See issue #19313 for a non-workaround proposal to address this.
+
+// One challenge here is that there can only be one copy of a top-level
+// module in a given compilation. That means that if this test uses
+// ./AutoMath.chpl as the AutoMath module, the internal library will
+// refer to it for things like min/max instead of the real one.
+
+// A related challenge to that, and part of the issue with Errors, is that in
+// order for this to work, the first use of AutoMath that the compiler seeks
+// to resolve has to be this one (vs one coming from somewhere else, e.g. an
+// already-parsed included module). That presents an ordering constraint that
+// causes problems when doing incremental or separate compilation. This issue,
+// combined with the limited number of modules to which this can apply, make
+// it potentially not worthwhile to support this pattern.
+
 use AutoMath;
 
 testmath();
diff --git a/test/modules/bradc/userInsteadOfStandard/foo2.good b/test/modules/bradc/userInsteadOfStandard/foo2.good
index 5b59d3473dd0..f591ae954976 100644
--- a/test/modules/bradc/userInsteadOfStandard/foo2.good
+++ b/test/modules/bradc/userInsteadOfStandard/foo2.good
@@ -1,3 +1,3 @@
 warning: Ambiguous module source file -- using ./AutoMath.chpl over $CHPL_HOME/modules/standard/AutoMath.chpl
-foo2.chpl:3: error: unresolved call 'testmath()'
-foo2.chpl:3: note: because no functions named testmath found in scope
+In my math!
+In my foo2