Python: Add markupsafe tests

python/ql/test/library-tests/frameworks/markupsafe/ConceptsTest.ql

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+import python
+import experimental.meta.ConceptsTest

python/ql/test/library-tests/frameworks/markupsafe/InlineTaintTest.expected

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+argumentToEnsureNotTaintedNotMarkedAsSpurious
+untaintedArgumentToEnsureTaintedNotMarkedAsMissing
+failures

python/ql/test/library-tests/frameworks/markupsafe/InlineTaintTest.ql

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+import experimental.meta.InlineTaintTest

python/ql/test/library-tests/frameworks/markupsafe/taint_test.py

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+from markupsafe import escape, escape_silent, Markup
+
+def ensure_tainted(*args):
+    print("ensure_tainted")
+    for x in args: print(" ", x)
+
+def ensure_not_tainted(*args):
+    print("ensure_not_tainted")
+    for x in args: print(" ", x)
+
+# these contain `{}` so we can use .format
+TAINTED_STRING = '<"TAINTED_STRING" {}>'
+SAFE = "SAFE {}"
+
+def test():
+    ts = TAINTED_STRING
+
+    # class `Markup` can be used for things that are already safe.
+    # if used with any text in a string operation, that other text will be escaped.
+    #
+    # see https://markupsafe.palletsprojects.com/en/2.0.x/
+    m_unsafe = Markup(TAINTED_STRING)
+    m_safe = Markup(SAFE)
+
+
+    # this 3 tests might look strange, but the purpose is to check we still treat `ts`
+    # as tainted even after it has been escaped in some place. This _might_ not be the
+    # case since data-flow library has taint-steps from adjacent uses...
+    ensure_tainted(ts) # $ tainted
+    ensure_not_tainted(escape(ts))
+    ensure_tainted(ts) # $ tainted
+
+    ensure_tainted(
+        ts, # $ tainted
+        m_unsafe, # $ MISSING: tainted
+        m_unsafe + SAFE, # $ MISSING: tainted
+        SAFE + m_unsafe, # $ MISSING: tainted
+        m_unsafe.format(SAFE), # $ MISSING: tainted
+        m_unsafe + ts, # $ tainted
+
+        m_safe.format(m_unsafe), # $ MISSING: tainted
+
+        escape(ts).unescape(), # $ MISSING: tainted
+        escape_silent(ts).unescape(), # $ MISSING: tainted
+    )
+
+    ensure_not_tainted(
+        escape(ts),
+        escape_silent(ts),
+
+        Markup.escape(ts),
+
+        m_safe,
+        m_safe + ts, # $ SPURIOUS: tainted
+        ts + m_safe, # $ SPURIOUS: tainted
+        m_safe.format(ts), # $ SPURIOUS: tainted
+
+        escape(ts) + ts, # $ SPURIOUS: tainted
+        escape_silent(ts) + ts, # $ SPURIOUS: tainted
+        Markup.escape(ts) + ts, # $ SPURIOUS: tainted
+    )
+
+    # flask re-exports these, as:
+    # flask.escape = markupsafe.escape
+    # flask.Markup = markupsafe.Markup
+    import flask
+
+    ensure_tainted(
+        flask.Markup(ts), # $ MISSING: tainted
+    )
+
+    ensure_not_tainted(
+        flask.escape(ts),
+        flask.Markup.escape(ts),
+    )
+
+
+test()